希土類酸化物RMnO3における元素置換効果と化学圧
力効果
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言語: English
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公開日: 2020-12-15
キーワード (Ja):
キーワード (En):作成者: バオ, ジンファ
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https://doi.org/10.15118/00010334

Thesis for a Degree of Doctor of Engineering

Effects of Element Substitution and Chemical Pressure
on Rare-Earth Oxide RMnO3（希土類酸化物 RMnO3 における元素置換効果と化学圧力効果）

BAO JIANHUADivision of Engineering
Course of Advanced Production Systems Engineering
Muroran Institute of Technology
September 2020

Abstract
The ABO3 type perovskite RMnO3 (R: rare-earth element) has investigatedextensively as the multiferroic materials which possess two or more types of orders
simultaneously. In this thesis, we investigated the effect of element substitution andchemical pressure in orthorhombic GdMnO3 (space group Pnma) and hexagonal
TmMnO3 (P63cm).
The X-ray diffraction measurement results of GdMnO3 shows A-type
antiferromagnetism is below TN, but it is known that Mn spins are not perfectly
antiparallel, but exist with a slight tilt. This is called cant magnetism or weakferromagnetism. The crystal structure of GdMn1-xCoxO3 is orthorhombic for 0≤x≤1.0.
For x=0.3, 0.5, and 0.7, at the ordering temperature TC, the field-cooled (FC)magnetization MFC rapidly increase which results from cating of the Mn and Co
moments with decreasing temperature. Especially, MFC for x= 0.3 showed maximum
values at 40K, decreased rapidly with decreasing temperature and showed a negative
magnetization blow 20K. On the other hand, the heavy rare earth oxide TmMnO3 is thatan antiferromagnetic transition temperature TN is 41K, and ferroelectric transition
temperature TC is 86K. It is known that the crystal structure of RMnO3 having thisstructure changes to the orthorhombic (Pnma) by performing high-pressure synthesis,but even in TmMn1-xCoxO3 with substitution by Co the structure changes fromhexagonal to an orthorhombic, and we can obtain an orthorhombic single phase (space1

group Pnma) at 0.5≤x. MFC of TmMn1-xCoxO3 was increase in ferromagnetically atabout 60K with decreasing temperature, and also showed negative magnetization in 0.7≤x. but MFC for x=0.8 no longer showed a ferromagnetic increase with decreasing
temperature. The increase in ferromagnetic magnetization with decreasing temperature
at TC can be understood as a result of the mixed-valence state due to Co substitution.
the negative magnetization observed in both samples. So-called the spin reversal, canbe explained by the antiferromagnetic coupling of the Gd or Tm spin to the Mn and Co
moments.
We

also

investigatedGd1-yRyMn1-xCoxO3

and Tm1-yRyMn0.5Co0.5O3(R:nonmagnetic rare-earth element) with substitution by nonmagnetic rare- earth elements
La, Y, Lu. We can expect the chemical pressure effect due to the unit-cell volume (V)change by substituting Tm or Gd with nonmagnetic rare-earth elements. From Tm1-y(Y,Lu)yMn0.5Co0.5O3 observation we can obtained some remarkable structural details:
owing to the ion radii, V of Tm1-yLuyMn0.5Co0.5O3 and Tm1-yYyMn0.5Co0.5O3 decreases
and increases with increasing y, respectively; the parameter (a−c)/a, which ischaracterizes the orthorhombic distortion, continuously increases on Lu doping anddecreases on Y-doping due to the substitution of Tm ions. Substitution of Tm with Y or
Lu in orthorhombic Tm1-y(Lu, Y)yMn1-xCoxO3induces a systematic unit-cell volume
change. This is the chemical pressure effect. From the magnetization measurement, weconclude that an increase of MFC and the unit-cell volume is responsible for the increasein transition temperature TC. We also studied the effects of chemical pressure with Gd12

yRyMn1-xCoxO3 y = 0.1, 0.3, and 0.5. The substitution of Gd with La, Y, or Lu in

orthorhombic Gd1-yRyMn1-xCoxO3 induced a systematic change in the unit-cell volume.
Our results reveal that increasing or decreasing the average ionic radius of the rare-earth
element in the compound affects the magnetic ordering temperature TC. The reductionin the proportion of Gd owing to substitution by nonmagnetic elements weakens thespin reversal effect.

3

論 文 内 容 の 要 旨
ABO3 型ペロブスカイト RMnO3（R:希土類元素）は同時に複数の秩序状態を持つマルチフェロイック物質として広く研究されている。本論文では、直方晶
GdMnO3（空間群 Pnma）と六方晶 TmMnO3（P63cm）について、元素置換効果と化学圧力効果を調べた。
GdMnO3 の X 線回折測定結果は、TN 以下で A タイプの反強磁性であることを示しているが、Mn スピンは完全には反平行でなく、わずかにチルトしていることが知られている。これはキャント磁性あるいは弱強磁性と呼ばれている。
この系の Mn を Co で置換した GdMn1-xCoxO3 の結晶構造は、0≤x≤1 で直方晶系である。x=0.3,0.5,0.7 では、転移温度 Tc において磁場中冷却(FC)磁化 MFC は、
温度低下とともに Mn と Co モーメントのキャントの結果として急激に増加する。特に、x=0.3 の MFC は約 40K で最大値を示し、温度の低下とともに急激に減少し、20K 以下では負の磁化を示した。他方、重希土類酸化物 TmMnO3 は、反強磁性転移温度 TN が 41K, 強誘電転移温度 TC が 86K である。この構造を持
つ RMnO3 の結晶構造は、高圧合成により直方晶に変化することが知られてい
るが、Co で置換した TmMn1-xCoxO3 においてもその構造は x に依存して六方晶から直方晶系へ変化し、0.5≤x では、錯体重合法により直方晶単相（Pnma）を得た。TmMn1-xCoxO3 の MFC は、温度の減少とともに、約 60K で強磁性的に増加し、0.6≤x≤0.7 でも負の磁化を示す。しかし、x=0.8 の MFC はもはや温度低下
とともに強磁性的な増加を示さない。これらの温度低下に伴う Tc での強磁性的な磁化の増大は、Co 置換による混合原子価状態の結果として理解できる。
4

また負の磁化、すなわちスピン反転は、Mn と Co モーメントに対する Gd ある
いは Tm スピンの反強磁性的カップリングによって説明できる。
我々はまた、Gd や Tm を非磁性希土類元素 La、Y、Lu で置換した Gd1-yRyMn13+

xCoxO3 と Tm1-yRyMn1-xCoxO3 の物性についても調べた。Gd、Tm3+、La3+、Y3+、

Lu3+のイオン半径の違いから、我々は、Tm または Gd を非磁性希土類元素で置換することによる単位格子体積(V)の変化による圧力効果を期待できる。
Tm1-y(Y, Lu)yMn0.5Co0.5O3 の調査から、いくつかの顕著な構造の詳細が得られた。
Tm1-yLuyMn0.5Co0.5O3 と Tm1-yYyMn0.5Co0.5O3 の V は、それぞれ y の増加とともに減少と増加した。直方晶歪みを特徴づけるパラメータ(a-c)/a は、Tm イオンを置換するために、Lu ドープでは連続的に増加し、Y ドープでは減少する。
直方晶 Tm1-y(Y, Lu)yMn0.5Co0.5O3 における Tm の Y または Lu による置換は、系
統的な単位格子体積の変化を誘起する。これは化学圧力効果である。磁化測定から、我々は MFC と単位胞体積の増加が転移温度 TC における増加に寄与すると結論する。直方晶 Gd1-yRyMn0.7Co0.3O3(R=非磁性希土類元素) の y=0.1,0.3,0.5
についても、化学圧力効果の研究を行った。Gd1-yRyMn1-xCoxO3 における Gd のLa, Y, Lu 置換は、単位胞体積の系統的な変化を誘起する。我々の結果は、化合物の希土類元素の平均イオン半径の増加あるいは減少が、磁気転移温度 TC に影響することを示す。非磁性元素による置換で生じた Gd の割合の減少は、ス
ピン反転効果を弱める。

5

Content
Chapter I .................................................................................................................................... 8

1.1 Multiferroic Materials ......................................................................................................... 9

1.2 History and Development .................................................................................................. 11

1.3 Classification ..................................................................................................................... 14
1.3.1 Single-Phase Multiferroic ........................................................................................... 14
1.3.2 Composite Multiferroic .............................................................................................. 19
1.4 ABO3 Type Multiferroic .................................................................................................... 20

1.5 RMnO3............................................................................................................................... 23
1.5.1 TmMnO3 ..................................................................................................................... 25
1.5.2 GdMnO3 ..................................................................................................................... 29
1.6 Purpose .............................................................................................................................. 32

Chapter II ................................................................................................................................. 33

2.1 Preparation methods .......................................................................................................... 34
2.1.1 Solid State Reaction Method ...................................................................................... 34
2.1.2 Complex Polymerization Method ............................................................................... 36
2.2 Experimental Method ........................................................................................................ 38
2.2.1 X-ray fold measurement and structural analysis ........................................................ 38
2.2.2 Magnetization Measurement ...................................................................................... 40
Chapter III ............................................................................................................................... 42

3.1 TmMn1-xCoxO3 ................................................................................................................... 43
3.1.1 Structure Analysis ...................................................................................................... 43
6

3.1.2 Magnetic properties .................................................................................................... 45
3.1.3 Conclusion .................................................................................................................. 51
3.2 Tm1-yYyMn0.2Co0.8O3.......................................................................................................... 52
3.2.1 Structure analysis........................................................................................................ 53
3.2.2 Magnetic measurement ............................................................................................... 57
3.2.3 Conclusion .................................................................................................................. 62
3.3 GdMn1-xCoxO3 ................................................................................................................... 63
3.3.1 Structure Analysis ...................................................................................................... 63
3.3.2 Magnetic Properties .................................................................................................... 67
3.3.3 Conclusion .................................................................................................................. 72
3.4 Gd1-yRyMn0.7Co0.3O3 .......................................................................................................... 72
3.4.1 Structure analysis........................................................................................................ 73
3.4.2 Magnetic properties .................................................................................................... 76
3.4.3 Conclusion .................................................................................................................. 81
3.5 TmMn1-xFexO3 ................................................................................................................... 81
3.5.1 Structure Analysis ...................................................................................................... 82
3.5.2 Magnetic properties .................................................................................................... 83
Chapter IV ............................................................................................................................... 85

References ............................................................................................................................... 89

Publications ............................................................................................................................. 93

Acknowledgments ................................................................................................................... 94

7

Introduction

Chapter I

Introduction

8

Introduction

1.1 Multiferroic Materials
Ferroelectric / piezoelectric materials are a class of dielectric functional materials,
occupying an important position in the fields of sensing, driving, and information
storage, forming disciplines such as "ferroelectric physics". Magnetic materials are still
extensively used and dominate, especially, as information storage, the development ofmagnetic storage technology produced a new subject "spintronics", etc. in general, theferroelectric / piezoelectric material is electrically insulating, and magnetic material iselectrically conductive, and thus are not usually two types of material compatible, they
belong to two different independent fields. Multiferroic materials combine two or moredifferent (ferroelectric / piezoelectric, and ferromagnetic) characteristics into one,ordered coexistence, and more importantly, new effects are generated due to the mutual
coupling of multiple order parameters. For example, ferroelectric / piezoelectric andmagnetic coupling generate magnetoelectric effects, which is polarization by theexternal magnetic field, or regulates magnetic in external electric field.
In dielectric materials, the order of electric dipoles produces and the polarization P
can be controlled by the electric field E, and the spontaneous polarization in
ferroelectricity occurs in zero electric field E0. On the other hand, the magnetization M,
which is produced by the order of spin can be controlled by the magnetic field H,
ferromagnetic has a spontaneous magnetization in zero applied field H0. However, in
9Introduction

multiferroic, have not only PE and MH characteristics, but also a magnetic-electric
cross-regulation effect, that is, the magnetization M can be regulated by the magnetic
field H or the electric field E as Fig .1 shows.

Fig. 1.1 Schematic diagram of the magnetoelectric effect of multiferroic

Multiferroic (magnetoelectric) material is a new type of multifunctional material,
it is basically literally understood, both having multiple "ferrous" is multiferroic. But
now the magnetoelectric multiferroic has widened this range, as long as it is magnetic(not only ferromagnetic) and polarized (not necessarily ferroelectric), it can be called
multiferroic, which can be used not only in the application field of a single ferrous
material, but also in the fields of new type magnetic-electric sensor devices, spinelectronic devices, new information storage devices, etc. On the other hand, the physicalconnotation of multiferroic-electrical coupling involves multiple categories ofcondensed matter physics such as electric charge, spin, orbit, and lattice; therefore, it
has become a new international frontier research area. From the perspective of thediscipline, multiferroic materials organically combine the two major types of materials

10Introduction

which ferroelectric and magnetic that have traditionally lacked intrinsic links with thefields of electronics with information and energy1,2).

1.2 History and Development
Wilhelm Conrad Röntgen discovered in 1888 that a dielectric became magnetizedwhen moving in a uniform electric field3). His study was motivated by the following
reasoning: when the polarized in the external electric field dielectric sheet moves in the
direction perpendicular to the field line, the motion of negative and positive charges,
separated through the induced polarization, then becomes equivalent to two electricalcurrents moving into opposite directions on either side of the sheet. Those currents
generate a magnetic field, so the dielectric was magnetized. The experimental setup toprove the magnetoelectric effect did involve a fast-rotating dielectric disc between two
horizontal capacitor plates. In 1894, Curie pointed out through symmetry analysis thatthe intrinsic magnetoelectric coupling effect may exist in some crystals4). In the samecommunication, Röntgen also conjectured that the inverse effect should exist, namely
the change of the polarization of a moving dielectric induced by an external magnetic
field, which was indeed experimentally shown by Wilson in 19055). In 1961, American
scientists first reported that the intrinsic magnetoelectric effect was observed at low andmedium temperatures of Cr2O3, predicted by Dzyaloshinskii [6] on symmetry grounds,
was experimentally verified through the demonstration that an electric field did induce11Introductiona magnetization [7–9] as well as the reverse eﬀect, the magnetic field induce dielectricallypolarization [10] is making early. The study of magnetoelectric effect reached a small
climax in the 1970s, and low-temperature magnetoelectric effects were observed insome borate, phosphate, and manganate crystals. At the same time, the concept andmaterials of composite magnetoelectricity also appeared for the first time. However,
due to lack of practical application drive, low temperature conditions, and complicatedcoupling mechanisms, all related studies subsequently entered a trough " low ebb " ofnearly 30 years. Until the beginning of the 21st century, research on multiferroic
materials began [11].
The following briefly summarizes the development status and trends of singlephase and composite multiferroic materials and related components.
In the past ten years, with the advancement of material preparation technology,
characterization methods and theoretical calculations, and the urgent demand for new
information functional devices in the modern information society, the research on
multiferroic materials and related devices has experienced unprecedented rapid
development. International well-known journals such as “Nature” and “Science” havesuccessively reported the rich physical connotations and novel experimental
phenomena in multiferroic materials, which has caused great attention to multiferroicity
in the world. The research results published in the form of papers have grownexponentially. Since 2005, at the American Materials Research Society (MRS) of
materials

research,theannualconference
12

has

listed"multiferroicandIntroduction

magnetoelectricity" as one of the conference's chapters, attracting Many researchers
have participated and paid attention. At the end of 2007, Science “Areas To Watch” haslisted multiferroic materials as one of the seven leading research areas worthy ofattention in the future (European Large Hadron Collider, MicroRNA, artificial
microorganisms, paleogenomics, multiferroicity, human microbiome, neural circuits ofthe brain). Currently, the United States, Japan, Germany, France, China and othercountries have invested a lot of resources to carry out research on multiferroic materials.
The research scope of multiferroic materials mainly includes: 1) Electrical /magnetic functional materials science (ferroelectric materials, magnetic materials,
multiferroic materials); 2) solid state physics (strongly correlated condensed mattersystems,

Spin-orbit-charge-latticeinteraction);3)

spintronics(spintronics,

magnetoelectronics, multiferroic electronics); 4) physics and technology of electronic
devices.
In 2000, the American scientist Hill12) theoretically discussed the conditions
required for the coexistence of ferroelectricity and ferromagnetism in oxides. At thesame time, the development of thin-film preparation technology and advanced
characterization methods (Such as simultaneous observation of electric and magnetic
domains) has promoted the experimental research of single-phase multiferroic materials.
In recent years, there have been many review and articles summarizing and discussing
the research of single-phase multiferroic materials1~2,12~17). Among this, in 2009 Liu14)
research of Nanjing University, China, summarized the research progress in this field
13

Introduction

in a comprehensively and in detail, and the first review article published by the groupin Advanced Physics. Similarly, in 2018, we reported in detail the physical propertiesof perovskite manganese oxide TmMn1-xCoxO315) in the Journal of the Physical Societyof Japan, and analyzed the effect of Co substitution on TmMnO3, and summarized many
constructive conclusions.

1.3 Classification
From the perspective of material composition, multiferroic materials can bedivided into two types: single-phase compounds and composite materials. In the two
types of materials, the magnetoelectric effect has different origins.

1.3.1 Single-Phase Multiferroic
For single-phase multiferroic compounds, the mechanism of coexistence offerroelectricity and magnetic properties can be attributed to paramagnetic ion doping,structural anisotropy, asymmetric lone pair of electrons, geometric and electrostaticforce-driven ferroelectricity, and microscopic magnetoelectricity effects have beenfound in more than ten different system compounds, including bismuth ferrite (BiFeO3)
and rare earth manganese oxides, which have been widely studied. Although singlephase multiferroic compounds have intrinsic magnetoelectric effects, however, theCurie temperature (TC) or Neel temperature (TN) of most materials is very low, and it is14

Introductiondifficult to achieve a strong magnetoelectric coupling effect at room temperature.
BiFeO3 is currently the only single-phase multiferroic magnetoelectric material with atemperature above room temperature over the past few years. Curie temperature andNeel temperature materials have been widely studied. However, BiFeO3 is G-type
antiferromagnetic or weakly ferromagnetic, and its magnetoelectric coupling effect isweak, which limits this kind of multiferroicity to a certain extent practical applicationof compounds. The intrinsic magnetoelectric effect of single-phase multiferroic
compounds is still in the fields of materials and physics in recent years due to its rich
physical connotation and its application prospects in fields such as spin electronics andpolymorphic storage. Cause the research boom has sought to find single-phasemultiferroic compounds with strong magnetoelectric coupling effects at room
temperature, and exploring their physical mechanisms has become an important
direction in the field of multiferroic research.
In recent years, the research status and development trends of the new single-phasemultiferroic system can be summarized into the following aspects.
1.

Synthesis and magnetoelectric coupling mechanism and application of singlephase multiferroic materials. It is mainly to explore the new material system
including ferroelectric, ferromagnetic and significant magnetoelectric
coupling of type I and II multiferroic materials: type I Multiferroic materials
are mainly classified as perovskite oxides (such as BiFeO3, etc.), and also
contain some fluorides and sulfides, usually with higher ferroelectric Curie
15

Introduction

temperature and polarization strength, and higher magnetic Curie temperature.
type II multiferroic materials is mainly classified into spin-frustrated oxidesystems. The advantage is that the ferroelectricity is derived from the specificspin configuration and spin-orbit and spin-lattice coupling associated with thespin. Therefore, it has an intrinsic and significant magnetoelectric crossregulation effect. However, the nature of spin failure determines that its
magnetic moment is small, and the ferroelectric Curie temperature is low andthe polarization is small.
2.

Research on new effects of related electrons in multiferroic materials.
Multiferroic materials belong to a typical strongly correlated electronicsystem. Exploring and mining related new effects in multiferroic materials
originating from related electronic physics is also an important content ofmultiferroic research. First of all, the multiferroic material combines thecharacteristics of ferroelectric and ferromagnetic materials, and its energy gap
is between the wide band gap (2.5 ~ 5.0 eV) of a typical ferroelectric and thenarrow band gap (~ 1.0 eV) of a spin system. It shows a huge response toexternal stimuli. Typical effects include magneto-resistance, electroresistance, and resistive effect. These effects are important results related tothe physical connotation of electrons. Second, the complex band structure ofmultiferroic materials makes them more sensitive to photons. The excitation
has a strong response. Since the band gap of the multi-iron system is closer to16Introduction

the energy of visible and infrared photons, the energy band can be adjusted byspin and polarization, and in turn, the spin and polarization order parameters
can also be controlled by photon excitation, so it is of great value for thedevelopment of new optoelectronic functional materials. Again, the interface
between multiferroic materials and semiconductor materials is also worthy ofattention.
3.

In the research and development of multiferroic new materials, in addition tolarge-scale experimental exploration, multi-scale simulation calculations andfirst-principles calculations have played an indispensable role, providing a
multiferroic new material electronic structure design and synthesis favorable
analysis guidance tools: (1) Theoretical calculations provide a reasonable
explanation for the experimental phenomenon of multiferroic new materials.
(2) Theoretical calculations provide reference data for experimental research.
For example, first-principles calculations calculate the dual origin of
HoMn2O5 iron polarization, and simulate the microscopic mechanism ofpolarization generated in TbMnO3. (3) The cross-scale phase field calculation
provides a theoretical basis for the design of new multiferroic heterojunction
devices.

4.

From the perspective of scientific interest, more and more research in the
future will focus on several aspects such as the detection of new materials,
new structures, and novel quantum effects at the nanoscale in electronic
17

Introduction

correlation systems. On the other hand, for the application of future electronic
devices, how to face the challenges of high density, low energy consumption,high read and write speed is the core issue at present. With the birth of higher
material preparation equipment, people have started to pay more attention to
the high-quality crystal preparation under extreme conditions (ultra-highpressure single crystal growth, etc.), and atomic-level growth control of thinfilm materials (laser molecular beam epitaxy, etc.). Only in this way can we
provide a good model system for studying the mutual coupling of charges,
orbits, lattices and other degrees of freedom that may occur in related systems,
especially multiferroic materials, and then explore the derivation at smallscale domain walls and heterojunction interfaces singular physicalcharacteristics. Moreover, more advanced testing methods have enriched theresearches on multiferroic systems. Especially in the past few decades, the insitu growth measurement of materials under specific conditions by advanced
experimental methods applied to strongly correlated electronic systems in thefield of condensed matter may become one of the future development trendsofscientificresearch.

For

example,angle-resolved

photoelectron

spectroscopy, synchrotron radiation X-ray, etc. combined with laser molecularbeam epitaxy or molecular beam epitaxy. In addition to the exploration of
fundamental scientific issues, micro-nano processing technology will also
become a necessary means for the research of multiferroic materials based on
18

Introduction

ABO3. At present, many research teams have started to focus on theapplication of micro-processing technology on the basis of fully obtaining
high-quality crystals and material structures.

1.3.2 Composite Multiferroic
Composite multiferroic materials are completely different. The ferroelectric andferromagnetic phases that make up a magnetoelectric composite do not have amagnetoelectric effect, but the coupling between the two makes the ferroelectricferromagnetic coexistence system at room temperature. In a classic composite
multiferroic materials, the magnetoelectric effect is the “product” of themagnetostrictive effect (or piezomagnetic effect) in magnetic phase and thepiezoelectric effect (or inverse piezoelectric effect) in ferroelectric phase, indicatingthat the mechanical and electrical coupling between the two phases in the composite
multiferroic material is achieved by mechanical strain / stress transfer. When thecomposite multiferroics is placed in a magnetic field, the magnetic phase produces
strain due to the magnetostrictive effect, and the strain is transferred to the pressure. In
the electrical phase, the piezoelectric effect produces polarization. This is the positive
magnetoelectric effect, and its size is generally expressed by the magnetoelectriccoefficient α (or magnetoelectric voltage coefficient αE), which is generally expressedin V/cmOe. For composite multiferroic, the properties of the constituent phase materials
themselves, the microstructure formed after the composite, and the interface coupling

19

Introduction

coefficient are important factors. By adjusting the phase composition andmicrostructure, the magnetoelectric effect can be achieved optimization and formagnetoelectric composite design provides flexibility.

1.4 ABO3 Type Multiferroic
The most studied and generally used of multiferroic is ABO3 perovskite structureoxide. Among this structure, the ferroelectricity mostly comes from the B-site ion
located at the center of the oxygen octahedra, below the Curie temperature, it deviatesfrom the center of the oxygen octahedron, which reduces the symmetry of the crystal
structure and separates the positive and negative charge centers to an electric dipole
moment. ABO3 perovskite-structured ferroelectrics usually require no electrons in thed-orbital of the B-site ion showing d0 state. If there are zero electrons in the d-orbit, thelocal magnetic moment will not be formed, and all kind of magnetic ordered structure(including ferromagnetic, ferrimagnetic, and antiferromagnetic) can’t be generated. In
most cases, once the d-orbit of the B-site ion is partially occupied by electrons, its
tendency to deviate from the center of symmetry will eliminated. It can be seen that,the conventional ferroelectricity and magnetic orderly generation mechanism at theatomic scale are mutually exclusive, most of them magnetic perovskite is a centersymmetric cubic or orthorhombic structure, and the ferroelectric structure of theperovskite structure must be non-centrally symmetric. If there is a single-phase material
20Introductionthat allows ferroelectricity and ferromagnetism to coexist, then it must have a condition
that can satisfy both the symmetry of the ferroelectric crystal structure and theferromagnetic electronic shell structure.
At present, through first-principles calculations and fine experimental observations,many single-phase multiferroic systems have been continuously proposed. For example,
the perovskite compounds, chemical formulas like ABO3 or A2B′B′′O6, Such as BiFeO3,
BiMnO3, PbFe1/2Nb1/2O3; RMn2O5 (R = Y, Tb, Dy, Ho) in orthogonal structure;
M3B7O13X (M=Cr, Mn, Fe, Co, Cu, Ni, X = Cl, Br); BaMF4 compounds (M = Mg, Mn,
Fe, Co, Ni, Z), and rare earth manganese oxides, such as hexagonal RMnO3 (R = Sc, Y,
In, Ho, Er, Tm, Yb, Lu), etc.
Among these multiferroic compounds, the mechanisms by which ferroelectricity
and ferromagnetic coexist may be:1) Paramagnetic ion doping. Paramagnetic ion is used to partially replace thetransition metal ions of the outer electron arrangement such as inert gas,
which may produce "traditional" ferroelectricity and magnetic properties.
For example, in solid solution PbFe1/2Nb1/2O3 and [PbFe2/3W1/3O3]1x[PbMg1/2W1/2O3]x multiferrocity observed.

2) Structural anisotropy. Using the factors leading to structural anisotropy,
electrostatic double potential wells can be realized in paramagnetic ions. For
example, the diagonal apex of the octahedron is occupied by different ions.
M3B7O13X-type arborite is this mechanism.
21

Introduction3) Asymmetric lone pair of electrons. The ferroelectricity of the compound
BiRO3 (R = Fe, Mn, Cr) is derived from the hybridization of the s lone pairof electrons and the empty p-orbital to form a localized electron cloud, whichleads to structural distortion and triggers ferroelectric. On the other hand, Bsite magnetic ions contribute to the magnetism.
4) Ferroelectricity driven by geometry and electrostatic force. Ferroelectricity
is generated by geometric and electrostatic force drive in hexagonal
manganite.
5) Micro-magnetoelectric interactions. Orbital order, geometric magnetic
suppression, Jahn-Teller deformation, super-exchange and double-exchange
can produce significant electrical, magnetic, and stress-modulated micromagnetoelectric effects, such as in TbMnO3 and TbMn2O5 multiferrocity.
6) Frustrated magnet system. In the experiment, researchers have observed thecoexistence of ferroelectricity and ferromagnetism at low temperatures invarious compounds. For example, in the YMnO3 single crystal, the German
Fiebig team18) used the second harmonic method to observe for the first timethe domain structure formed by the interaction of the domain walls of theantiferromagnetic and ferroelectric domain, which is determined by the
product of the magnetic and electrical sequence parameters, thus revealing
the mechanism of magnetoelectric coupling. Induced by strong magnetic
field at a low temperature, the DyMnO3 single crystal produce a dielectric
22Introduction

constant change up to 500%, which is called the “colossal magneticdielectric effect”. TbMn2O5 single crystal is also observed at low
temperature the magnetic field regulates the dielectric and ferroelectric
properties, under the action of the magnetic field, the direction of thepolarization changes 180°, and this kind of reversal can be repeated manytimes. This phenomenon originates from the magnetic-induced phasetransition, which is most likely to be magnetically induced by Tb magnetism.
Based on the manganese oxide phase diagram, the Guoquan Zhang team19)of Nanjing University predicted that there may be huge ferroelectricity inthe system with strong antiferromagnetic interaction and weak Jahn-Teller
distortion mode, on the basis of which a new CaMn7O12 with excellent
performance was synthesized Multiferroic system.

1.5 RMnO3
In the many of study with single-phase multiferroic materials, the rare-earth
manganese oxide RMnO3 (R3+ is a rare-earth ion) is a most classics multiferroic with awide range of physical properties. It is typical example of the compound represented
by the composition formula of ABO3, RMnO3 has a different crystal structure
depending on the ionic radius of the rare earth element R (= Sc, Y, La to Lu). In thesynthesis under normal pressure, the hexagonal structure (space group: P63cm, Fig.1.1
23

Introduction

left side) for R = Sc, Y, Ho ~ Lu with relatively small ionic radius, the ferroelectricphase transition temperature (Curie temperature) of the hexagonal RMnO3 is about 5901000K20), and the orthorhombic perovskite structure (space group: Pnma, Fig.1.1 rightside) for R = La ~ Dy with relatively large ionic radius for R3+ (R = La-Dy) with a larger
ionic radius. If R3+ is partially replaced by A2+ (A = Ca, Sr, Ba) cations, the substance
exhibits a giant magnetoresistance effect. It is known that the crystal structure becomescubic when RMnO3 having this hexagonal structure is synthesized under high pressure,and it has both ferroelectricity and antiferromagnetism, and the antiferromagnetic phasetransition temperature (Neel temperature) is about 70K-130K22). The simple perovskite
structure (space group: Pm-3m, Fig. 1.2), which is an ideal perovskite structure, has Asite ion located at the corner of the cube, B-site ions are located at the body center, andoxygen ions are located at the face center of the cube. Six oxygen ions around the Bsite ion form a BO6 octahedron, and are connected three-dimensionally by sharing thevertices of the octahedron. It is thought that A-site ions are also located in gaps in thisMnO6 octahedral network. In an actual RMnO3 crystal, R ions do not have a sufficientionic radius to fill the octahedral gap, so that the octahedron is inclined and the crystal
structure often takes a perovskite-type rectangular structure deviated from cubic (asFig.1.2 shows).

24Introduction

Re

Mn

O

Fig. 1. 1 Rare earth crystal structure model of the manganese oxide RMnO3.

A
B

O

Fig. 1. 2 Cubic perovskite structure of ABO3.

25

Introduction

1.5.1 TmMnO3
The crystal structure of the heavy rare earth oxide TmMnO3 is hexagonal spacegroup (P63cm), antiferromagnetic transition temperature TN is 41K23,24), andferroelectric transition temperature TC is 86K. It is known that the crystal structureof RMnO3 having this structure changes to the orthorhombic (Pnma) by performing
high-pressure synthesis.
High-pressure synthesis is mainly used to synthesize substances composed of nonmetallic elements. The advantage of performing at high-pressure synthesis is that thesynthesis can be carried out under temperature conditions that cannot be achieved undernormal conditions. This is because the melting point of the substance increases whenpressure is applied. When determining the structure and state of a substance, pressure
is as important as temperature. Generally, a gas becomes a liquid when pressure isapplied, and becomes solid at higher pressure. With pressure increases, the solidchanges its crystal structure to a dense crystal structure, so the physical properties
change a lot, just like the pressure turns the insulator into a metal. The experimental
results show that h-TmMnO3 undergoes a phase transition from a hexagonal to an
orthorhombic structure at about 10.2 GPa24). The evolution of bond angles and bonddistances between Mn and O atoms under high pressure has been imply that themagnetic-ordering temperature will be enhanced with increasing pressure, which willaffect magnetoelectric coupling.

26

20

30

40 50 60
2 / degree

70

208

206
220 310
311
312
216
224
118

302

211
204
212

104
202

116

300

111
004
102

002
100

10

114

110

Relative Intensity

112

Introduction

80

Fig.1.3 Powder X-ray diffraction pattern of TmMnO3

From the magnetization measurement results (Fig 1.4 a), the overall magnetization
appears to be paramagnetic. However, separation of ZFC and FC was confirmed at TN~ 82K. This is thought to be due to the antiferromagnetic transition with Mn ions, whichis in good agreement with the reported value23,24). In the magnetization measurement,
the applied magnetic field was measured at both H = 250 Oe and 25 Oe, but it wasdifficult to determine the temperature of the separation with the applied magnetic fieldof 250 Oe. This is cause by the applied magnetic field is strength, the moment is directed,
so that the antiferromagnetic transition becomes difficult to observed.

27

Introduction

0.025
(a)

0.009

0.008
M / emu g-1

M / emu g-1

0.02
0.015

0.007

0.006
T ~ 82K

0.01

0.005
60

N

70

80
90 100Temperature / K

H = 25 Oe

0.005
0

110

TN ~ 82K

0

50 100 150 200 250 300 350
Temperature / K

0.7
(b)

0.5

CT

-1

-1

/ J mol K

-2

0.6

0.4
0.3
TN ~ 82K

0.2
0.1
0

TSch ~ 9.4K

0

20

40 60 80 100 120
Temperature / K

Fig. 1.4 Temperature dependence of magnetization (a) and specific heat (b) of
TmMnO3●: ZFC (zero magnetic field cooling magnetization) ■: FC (magnetic fieldcooling magnetization). Applied magnetic field is zero when measuring specific heat28

Introduction

In the results of specific heat measurement (Fig 1.4 b), the vertical axis isrepresented by C/T (specific heat C and temperature T). At TN ~ 82K, the peak was
observed of specific heat is considered to be due to antiferromagnetic transition, thisvalue corresponds to the separation of ZFC magnetization and FC magnetization due tothe antiferromagnetic transition observed at about 9.4K, which was considered to be
due to the Tm3+ Schottky anomaly.

1.5.2 GdMnO3
The X-ray diffraction measurement results of GdMnO3 (space group: Pnma)
obtained in the past studies are shown in Fig. 1.5, and the temperature dependence ofthe magnetization is shown in Fig. 1.6. Separation of MZFC and MFC is observed at TN ~30 K. This is thought to be due to the antiferromagnetic transition of Mn spins. GdMnO3shows A-type antiferromagnetism is below TN, but it is known that Mn spins are not
perfectly antiparallel, but exist with a slight tilt. This is called cant (anti)
ferromagnetism or weak ferromagnetism. Spins below the transition temperature arealigned in a slightly inclined state and exhibit an increase in ferromagnetic
magnetization. There are various causes of this spin gradient, and the DzyaloshinskyMoriya interaction (DM interaction) is considered to be one of the reasons. The DM
interaction is not given by the scalar product (S1 · S2) between two spin vectors that
express super-exchange interaction, but it has the form of a vector product (S1 × S2).
This interaction was phenomenologically guided by the introduction of symmetry of29

Introduction

the crystal and the symmetry operation of spin (time) inversion by Dzyaloshinsky, andclarified by Moriya from a microscopic point of view through the reflection of thecrystal symmetry and magnetic coupling. The Hamiltonian of DM interaction isexpressed by the following equation:

𝐻DM = 𝑫12 ・(𝑺1 × 𝑺2 )D12 is a DM vector and S1 and S2 are spin operators.
Here, we classically consider the energy stable state of two Heisenberg spin S1, S2
systems with DM interaction D12・(S1 × S2) in addition to the usual Heisenberg typeinteraction-J S1・S2. Since we think classically, we think of S1 and S2 as vectors oflength 1 (classical Heisenberg spin). If the angle between S1 and S2 is θ, the energy is J cos θ-Dsin θ. (D is the magnitude of DM interaction) If this is minimized with respectto θ,

tan 𝜃 =𝐷𝐽

The energy becomes stable at an angle θ that satisfies. In other words, when there
is DM interaction, the directions of adjacent spins incline to each other. The position of
the spin across the crystal in the presence of the DM interaction depends on how the Dvector exists in the crystal.
If the D vector has the same orientation, the position of the spiral spin is stable.
When the directions of the D vector are alternating, a spin structure of a type in which
inclined pairs of spins repeat periodically is stable. In the latter case, the30Introduction

antiferromagnetic component is added when the sign of the exchange interaction J isferromagnetic (J > 0), in the antiferromagnetic (J <0) case, a ferromagnetic component
is added.
121

60000

40000

0
10

20

40

50

242
004
313
412
422

202

210
002

30

212
301 040 230
103 311141 113321 240042 123
331
410

10000

112
220
022
122 131

101
020

20000

200

111

30000

011

Intensity / counts

50000

60

2 / degree

7080Fig.1.5 X-ray diffraction pattern of GdMnO3
14

M / emu g

-1

12
10
8
6
H = 250 Oe
4

ZFC
FC

2
0
0

50

100

150

200

250

300

350

Temperature / K
Fig.1.6 Temperature dependence of magnetization of GdMnO3

31

Introduction

1.6 Purpose
Replacing the Mn and (or) R site with another transition metal element in the rareearth manganese oxide RMnO3, shows that mixed valence perovskite composed of ionsof multiple valences (such as Mn4+, Mn3+, Co2+, and Co3+ Enables composition). This
causes a change in the Mn4+ / Mn3+ ratio and a new interaction between Mn and Co,
and the material exhibits various physical properties. Thus, the influence of substitutionof R or Mn sites in RMnO3 is very important in physical properties, but may also affectgeometric parameters such as lattice volume, average ionic radius of R site, Mn-O-Mnbond angle and tolerance factor. Research on replaced of the R site with another element
is known to be a system that replaces rare earth elements such as La1-xSrxMnO3 withdivalent alkaline earth metal elements, but simultaneously with changes in structuralparameters such as lattice volume. Substituting Mn with Co element also causes achange in the valence of Mn ions, which affects the magnetic properties as describedabove. In order to more clearly examine the effects of changes in structural parameterssuch as lattice volume and bond angle on the properties of rare-earth manganese oxides,
the structure analyses and magnetic measurements were performed in Tm1-yYyMn1xCoxO3. On the other hand, the Gd of Gd0.7Co0.3O3 is replaced with La, Y, and Lu, which

are trivalent, stable and nonmagnetic rare earth elements. The purpose of this study is
to investigate the magnetism of the ABO3-type perovskites systems. In addition, weclarify the effect of chemical pressure on magnetism in the mixed-valence system.

32

Experiment

Chapter II

Experiment33

Experiment

2.1 Preparation methods
2.1.1 Solid State Reaction Method
The solid-state reaction method is one of the classical sample preparation
methods and is mainly two or more substances (particles) generate new matter
through the chemical reactions. The microscopic process should be: reactant
molecules or ions contact plus chemical reaction to generate new material (break andformation of bonds). In solution reactions, the reaction molecules or ions can bedirectly contacted. In the solid phase reaction, the reactants are generally mixed in
the form of a powder, and the particle size of the powder is mostly on the order ofmicrometers, and the contact of the reactants is insufficient. Particles such as oxides
and carbonates of the elements contained in the target substance are mixed well in an
appropriate ratio using a ball mill or mortar, and then calcined at a high temperature
to reduce the contact between the particles of the base material. The diffusion of theions occurs, and the particles come into contact with each other through the reactant
layer to obtain the target substance. In fact, the solid reaction is the diffusion ofreactants in the crystal lattice through the particle contact surface. The diffusion rateis usually the determining factor of the speed and degree of the solid phase reaction.
Taking the preparation of Tm1-yYyMn0.3Co0.7O3 as an example, in the solid phasereaction method, the base material was weighed so that the total amount of the target
sample was 5 g. Powders of Tm2O3, Y2O3, Mn2O3 and Co3O4 were used as the base34

Experimentmaterial. The purity is 99.9% for Tm2O3, Mn2O3 and Co3O4 and Y2O3 for99.99%. In
order to accurately weigh the sample and dried in an oven at 200°C. for about 24
hours, and then each base material was weighed so as to obtain a target sample. The
weighed value was determined from the following formula:(1-y) Tm2O3 + yY2O3 +3
10

Mn2O3 +

14

Co3O4 + ∞O2 → 2Tm1-yYyMn0.3Co0.7O3

30

The weighed sample was thoroughly mixed in an agate mortar for 1 hour to makeit uniform. After applying a pressure of about 500 kg / cm2 to form pellets, it was
calcined twice on an alumina boat. The calcination condition is that the temperatureis heated from room temperature to 1150°C within 8 hours and then maintained for
24 hours, then naturally cooled to room temperature within 8 hours. Normally, we
calcined in powder state, but in the sample containing Co, the contact surface
between the firing boat and the sample became blue due to the collapse of the sample
caused by the body release and the distribution of the oxygen atmosphere throughout
the sample, which indicates that Co3O4 as one of the basic materials may haveescaped. Therefore, in order to minimize the contact surface between the alumina
boat and the sample, it is mainly compressed and solidified to increase the sintereddensity, and granulated before calcination, and calcined in a granular form.
Co3O4 is a black solid and is a mixed valence compound containing Co2+ andCo3+. The substance can be stable at temperatures up to 600 to 700°C, but when it
exceeds 950°C, it will decompose with oxygen and stabilize to CoO with Co2+, thespecific reaction formula is as follows:
2Co3O4 → 6CoO+O2 (950° C)
35

Experiment

CoO is a black or gray powder, also known as colorant or cobalt blue. As a result,it can be considered that as the amount of Co3O4 substitution increases, the amountof CoO remaining in the alumina boat increases.
The electric furnace we use is a silicon electric furnace, it is composed of adigital program temperature control system, a single-phase power feedback thyristor
regulator and a rotary vacuum pump that control the output voltage to be constant.
In order to prevent the lack of oxygen in the synthetic sample, calcination is carriedout in an atmosphere filled with oxygen. in order to replace Mn with Co, must be
create a pure environment, at first, put the sample in an electric furnace and thenwash it with oxygen 3 times or more.

2.1.2 Complex Polymerization Method
The solid-state reaction is a method in which an oxide or a carbonate is
physically mixed as a starting material and sintered at a high temperature. Since
calcination at a high temperature is required, sintering proceeds and fine particles of
the composite oxide cannot be obtained (As described in 2.1.1). In addition, since
the composition is biased due to the non-uniform particle size of the starting material,
it is necessary to repeat milling, mixing and firing, and this is a synthesis method thatis extremely disadvantageous in terms of energy. In the early stage of the research,
samples were prepared by the above method, but it was confirmed that Co3O4 of thebase material escaped due to high-temperature sintering, and that Tm2O3 was mixed
in the low Y concentration range (0≤y≤0.5). There were problems such as being done.
36Experiment

Therefore, our laboratory focused on the complex polymerization method, which isa new sample preparation method.
As one of the prescriptions for maintaining the uniformity of the composition, amethod of synthesizing a metal complex precursor having the same metalcomposition as the composite oxide and developing the target composite oxide byheat treatment has been developed. In general, in the complex polymerization method,a metal nitrate is dissolved in an aqueous solution containing a hydroxycarboxylic
acid such as citric acid, tartar or malic acid, and the solution is heated to synthesize
a gelled metal carboxylic acid complex. The gel is dried and calcined to form anoxide.
In the complex polymerization method, a base material was weighed so that a
total of 2.5 g of a target sample was prepared. Tm(NO3)3·4H2O, Y(NO3)3·6H2O,
Mn(NO3)2·6H2O, and Co(NO3)2·6H2O were used as base materials. Since
Mn(NO3)2·6H2O is a gel at room temperature, it was weighed after making it liquidwith hot water. Further, it is difficult to weigh the liquid according to the weighedvalue, and the liquid was actually weighed more than the weighed value. Based on
the weighed value of Mn (NO3)2·6H2O, the weighing calculation of another basematerial was performed again, and each base material was put into a beakercontaining pure water and dissolved. Thereafter, citric acid was added and the
mixture was stirred for 1 hour. Citric acid has a role of complexing a plurality ofmetal species and gelling the solution. After stirring, the temperature of the solution
was set to 70°C. Using a hot plate, and the solution was further stirred for 1 hour.
37Experiment

Thereafter, ethylene glycol was added. Ethylene glycol serves as a polymerization
accelerator by esterifying a plurality of complexed metal species into a polyester.
Since the solution containing the metal nitrate thus obtained contains a large amountof water, the water was evaporated at 90 to 130°C for several days. Since this is acomplex synthesis in the presence of a large amount of water, hydrolysis may
proceed rapidly and precipitation of a hydroxide may occur before a metal complex
is obtained. When such a phenomenon occurs, uniformity of the composition cannot
be maintained. Therefore, in the process of evaporating the water, the temperature
was adjusted in detail. After the gel precursor was obtained, it was heated at 300 to
400°C. until it became a powder in order to remove organic substances contained in
the sample. The obtained powder was put in an alumina boat and calcined using anelectric furnace. The firing conditions are as follows: the temperature is raised fromroom temperature to 900°C. in an air atmosphere over 6.5 hours, the temperature ismaintained for 7 hours, and the furnace is cooled down to room temperature over 6.5
hours. In the second main firing, firing was performed under the same firingconditions as above in an oxygen atmosphere after forming into pellets.

2.2 Experimental Method
2.2.1 X-ray fold measurement and structural analysis
In this study, the X-ray diffractometer (Mini Flex) manufactured by Rigaku Co.,
38

ExperimentLtd. was used for simple measurement such as investigation of X-diffraction pattern
and measurement with an accuracy higher than that required for analysis.
Since the shape of the sample could be solid after firing, it was pulverizedsufficiently in a mortar and finely powdered for measurement. The powdered sample
was placed in a concave portion of a glass sample holder, and another glass plate wasused to fill the concave and convex portions uniformly so that the sample surface andthe reference surface were aligned.
Measurement conditions is using Cu target, tube voltage 30 kV, tube current 10
mA, operation mode: continuous, scan range: 10° -80°, step width 0.02, scan speed
1.0 deg / min.
If the diffraction intensity pattern of the sample with good crystallinity ismeasured by an ideal device, it should be observed as a very sharp peak-shaped
pattern. However, in the actually-observed powder diffraction data, each diffraction
peak has a finite width, mainly due to the influence of "blur" due to the apparatus.
Diffraction peaks may spread due to imperfections (finite size, strain) of crystals inthe sample due to the influence of scattered light, fluorescence, stray light, electricalnoise, etc., a finite intensity (background) usually appears at diffraction angles otherthan the peak position. In the Rietveld method, a peak shape model function (profile
function) is placed at the calculated peak position, and the total diffraction intensity
figure is calculated as the sum with the background model function. The least squares
method is used for the optimization calculation in the Rietveld method. How to fit
individual peaks (fitting), in order of (1) peak intensity, (2) peak position, (3) peak
39

Experimentwidth, (4) peak shape (distortion), (5) peak shape sharpness A strong influenceappears. Among these, (1) parameters related to strength (type of atom, site
occupancy g at atomic position and x, y, z coordinates of atom, atomic displacement
parameter B) and scale factor (factor that multiplies the whole intensity figure by aconstant) , There are selective orientation parameters depending on the orientation of
the diffraction plane, and (2) the peak position is affected by the lattice constants (a,b, c, α, β, γ) and the peak shift parameter. The values of (3), (4), and (5) are assumed
to be represented by an appropriate model function that depends on the diffraction
angle and the diffraction plane orientation, and the parameters that characterize thismodel function are optimized. In this study, the program RIETAN-FP and X’pertHigh Score was used for Rietveld analysis.

2.2.2 Magnetization Measurement
For the magnetization measurement, a magnetic property measuring device
MPMS manufactured by Quantum Design Co., Ltd. installed in the lab was used.
This device is a high-sensitivity magnetometer equipped with a superconducting
quantum interference device (SQUID) and is a measuring device that can detect
minute changes in magnetic flux of a substance. It is used to investigate the magnetic
properties of various organic and inorganic compounds. This device can measure themagnetic field dependence and temperature dependence of the magnetization. Dueto its extremely high sensitivity, it is possible to measure not only ferromagnetic
materials but also paramagnetic materials and diamagnetic materials. It can also be
40Experimentapplied to samples with a small total magnetization, such as magnetic thin films andnano-magnetic particles. After setting the sample in the device, temperature control
and data acquisition can be controlled by a computer, and the measurement sequencecan be set up on a personal computer.
A part of the measurement sample was cut out from the fired pellet-shaped
sample and shaped with a cutter or sandpaper (# 1,000, 2,000). For measurement, set
the sample in a straw with a length of 200 mm and an inner diameter of 5 mm. Uponshaping the sample, the shape was made into a spheroid. In general, when the larger
the cross-sectional area perpendicular to the direction of the magnetic field and thethinner the magnetization direction, the larger demagnetizing field. The sample wasshaped into a wire-shaped spheroid to reduce the influence of such a demagnetizing
field. After shaping, the sample was weighed and fixed inside by using cellophanetape so that the position of the sample was about 7 cm from the end of the straw. The
air bubbles created between the cellophane tape and straws were pierced with sharp
tweezers or thumbtacks.

41

Experimental Results and Discussion

Chapter III

Experimental Resultsand Discussion

42Experimental Results and Discussion

3.1 TmMn1-xCoxO3
As part of this research, we prepared TmMn1-xCoxO3 (0.0≤x≤1.0) in which Mn of
TmMnO3 was replaced by Co and investigated its structure and magnetism. We werecompare the solid-state reaction and complex polymerization to find which better method
for sample preparation, and the sample was evaluated by X-ray diffraction andmagnetization measurement by MPMS.

3.1.1 Structure Analysis
Figure 3.1 shows X-ray diffraction (XRD) patterns for TmMn1-xCoxO3 prepared by
CP (complex polymerization method), with the XRD pattern for Tm2O3 included as areference (pink line). TmMnO3 (x=0), which was prepared by the SSR (solid-state
reaction method) was hexagonal. These XRD patterns were refined by Rietveld, and we
obtained the lattice parameters a, b, c and the unit cell volume V in Fig. 3.2, along withthe mass fraction of the hexagonal and orthorhombic phases shown in the inset, all as afunction of x. The inset in Fig. 3.2 shows the mass fraction of the components of the SSR
samples. Hexagonal and orthorhombic phases coexist for 0≤x≤0.5 in samples prepared byeither the SSR or CP. For 0.5 ≤ x ≤ 0.9, the CP samples are almost single-phaseorthorhombic, while the SSR samples contain a small amount of Tm2O3. The amount of
this impurity increases with increasing x. This indicates that the CP method is superior to
the SSR for the synthesis of samples with 0.5<x≤0.9. The space group for the hexagonalphase is P63cm, and the orthorhombic phase is a distorted perovskite with the space group43

Experimental Results and Discussion

Pnma. The lattice parameters ah, ch, and Vh in the hexagonal phase are almost constant
except for x=0.4. It is thought that the discrepancies for x=0.4 are caused by errors due tothe small mass fraction of the hexagonal phase. The lattice parameters ao, bo, co, and Vo
for the orthorhombic phase decrease with increasing x for 0.5≤x≤0.9. This is presumably
related to the ionic radii in TmMn1-xCoxO3. Peña et al. suggested that for ErMexMn1-xO3,
the general formula is of the type RE3+Mn4+1-xCo2+1-xCo3+2x-1O2-3 (RE=rare earth element),
when the substitution at the manganese site exceeds 50%.23) If we assume this valence
state formula for TmMn1-xCoxO3, then the average ionic radius of the 3d transition metal
ions in TmMn1-xCoxO3 decreases. This would qualitatively account for the decrease in thelattice parameters and the unit cell volume.

Fig. 3.1 X-ray diffraction patterns for various TmMn1-xCoxO3 samples.
The XRD pattern for Tm2O3, which is considered an impurity.

44Experimental Results and Discussion

6.2
ah
Vh
5.8

ch /2
5.6

60
40

370

20

hexagonal

00

0.2 0.4 0.6 0.8
Co concentration x

1

360
220

ao

5.4

co
0

Vo

0.5

0.2

210

〇

3

bo /2

5.2
5

380

orthorhombic

80

unit cell volume / A

lattice parameters / A

6〇mass fraction / %100

TmMn1-xCoxO3
0.4
0.6
0.8
Co concentration x

1200

Fig. 3.2 Lattice parameters and unit cell volume as a function of x. Open symbols are
obtained from Ref. 24. The inset plots mass fraction vs. x. All these values, except for
those for x=0, were obtained from samples prepared by complex polymerization.

3.1.2 Magnetic properties
Figures 3.3 and 3.4 plot, respectively, the temperature dependence of the field-cooled(MFC) and zero-field-cooled (MZFC) magnetization for the 0≤x≤0.4 SSR samples26) andthe 0.5≤x≤0.9 CP samples in a magnetic field of 250 Oe. The insets of Figs. 3.3 and 3.4
respectively show the mass fraction of the SSR samples and the temperature dependenceof FC-1 = H/MFC for the CP samples above 20 K. MFC increases ferromagnetically below
60 K with decreasing temperature for 0.1≤x≤0.7, and MFC increases in going from x=0.1
to 0.5 and decreases from x=0.5 to 0.9. With increasing x, the mass fraction of theorthorhombic phase increases, as do MFC and MZFC. A discrepancy is observed between
45

Experimental Results and Discussion

MFC and MZFC below about 160 K for 0.1≤x≤0.3, where the hexagonal and orthorhombic
phases coexist, and MFC and MZFC exhibit a different temperature dependence below
about 60 K. The MFC and MZFC for x≧0.5, where the main phase is orthorhombic, aredifferent below about 60 K. The appearance of the orthorhombic phase induces a rapid
increase in magnetization below 60 K. For x=0.8 and 0.9, there is no ferromagnetic
increase, but a separation between MFC and MZFC can be seen below about 60 K. We will
discuss the temperature dependence of MFC for the orthorhombic phase at low
temperatures in more detail below.

6
H = 250 Oe
5mass fraction / %100

4

M /emu g-1

3
2

orthorhombic

80
60
40

hexagonal

20

Tm2O3

0
0

1

0.2

0.4

0.6

0.8

Co concentration x

1

x=0.4
0
x=0.3
0
x=0.2
0
x=0.1

0
0

x=0.0
0

20

40

60

80

100

120

Temperature /K
Fig. 3.3 Temperature dependence of field-cooled (FC, filled symbols) and zero-fieldcooled (ZFC, open symbols) magnetization for TmMn1-xCoxO3 for 0.0≤x≤0.4, preparedby solid-state reaction. The inset plots mass fraction vs. x for samples prepared by solidstate reaction.
46

Experimental Results and Discussion

Fig. 3.4 Temperature dependence of FC (filled symbols) and ZFC (open symbols)
magnetization for TmMn1-xCoxO3 for 0.5≤x≤0.9.

6.5

25
TmMn1-xCoxO3

Co3+HS

-1

15
6

10
experimental

Co3+LS

5
0

5.5



-5

Weiss temperature / K

Peff / B mag.atom

20

-10
5
0.5

0.6

0.7
0.8
Co concentration x

-15
0.9

Fig. 3.5 Effective paramagnetic moment Peff and Weiss temperature  as a function of x
for TmMn1-xCoxO3. Filled (open) symbols are the experimental (calculated) Peff data forthe two-spin states of Co3+.
47

Experimental Results and Discussion

The inverse susceptibility of TmMn1-xCoxO3 (0.5≤x≤0.9) above 130 K, shown in theinset of Fig. 3.4, can be fitted as a linear function of temperature, that is, by the CurieWeiss law:

χFC =

𝑀FC
𝐻

=

𝐶
𝑇−𝛩

——————————（1）where C is the Curie constant,  is the Weiss temperature, and H is the external
magnetic field. C is related to the effective paramagnetic magnetic moment, Peff, via

𝑃eff 2 =

3𝐶𝑘B
𝑁𝜇B 2

————————————（2）where N is the magnetic atom (Tm, Mn, Co) number per gram, B is the Bohr magneton,and kB is the Boltzmann constant. The values of Peff and  obtained from MFC, are plottedin Fig. 3.5 as a function of x. It can be seen that , which is about 15 K for x=0.5,
decreases with increasing x, and is negative for x≧0.8. It is found that ferromagnetic andantiferromagnetic interactions predominate for x≤0.7 and x>0.7, respectively. Peff also
decreases with increasing x. Ghiasi et al. investigated the valence states of Mn and Co in
LaMn1-xCoxO3 nanoperovskites by X-ray absorption spectroscopy.27) They obtained theresults that LaMn0.75Co0.25O3 contained Mn3+, Mn4+, and Co2+, while LaMn0.25Co0.75O3
contained Mn4+, Co2+, and Co3+, and LaMn0.5Co0.5O3 contained Mn3+, Mn4+, Co2+, andCo3+. In order to facilitate the discussion, we will again assume the following valence
state formula for REMn1-xCoxO3 for x ≧ 0.5: RE3+Mn4+1-xCo2+1-xCo3+2x-1O2-3. Amongthese ions, Co2+ and Co3+ can have S=3/2 (high spin, HS) or S=1/2 (low spin, LS), and
S=2 (HS) or S=0 (LS) states, respectively. Assuming that the theoretical paramagnetic
moments of Tm3+, Mn4+, and Co2+ are 7.57 B, 3.87 B, and 3.87 B (HS), respectively,
at x = 0.5, a Peff equal to 6.01 B per atom is obtained for these magnetic atoms from48

Experimental Results and Discussion

Equation:𝑃𝑒ff = √∑ 𝑝𝑖 22——————————（3）The 2 in the dominator of Equation above is corresponds to the number of magnetic atoms
in the formula TmMn1-xCoxO3. This calculated Peff is close to the experimental value. It
is concluded from the Peff value for x=0.5 that Co2+ must be HS. In Fig. 3.5, the x
dependence of Peff is also shown for Co3+(HS) and Co3+(LS). If the electronic state of
Co3+ for x>0.5 is HS, Peff increases with x. This contradicts the experimental results in
Fig. 3.5. The values of Peff agree qualitatively with calculations in which Co2+ and Co3+
were assumed to be in the HS and LS states, respectively.
For 0.5≤x≤0.7, both MFC and MZFC increase ferromagnetically at TC  58 K withdecreasing T. Since the ferromagnetic interaction is predominant for 0.5≤x≤0.7, thisincrease in magnetization is thought to be due to the canted magnetic transition of the Mn
and Co ions, as reported for other rare-earth manganese oxides. The maximum values of
MFC are observed between 25 and 35 K. MFC decreases with decreasing T and shows
negative values below Tcomp  13 K for x=0.7. No ferromagnetic increase ofmagnetization is seen for x=0.8 and 0.9, though a small peak can be seen at about 44 K
in MZFC for x=0.8. The discrepancy between MFC and MZFC for x=0.8 and 0.9 is thought
to be due to antiferromagnetic ordering or competition between ferromagnetic andantiferromagnetic interactions.

49Experimental Results and Discussion

6

x=0.5

5

MFC / emu g -1

4
3

x=0.6

2
1

x=0.7

0

TmMn1-xCoxO3-1

H=250 Oe

-2
0

20

40

60

80

100

120

Temperature / K
Fig. 3.6 Temperature dependence of MFC for x = 0.5 to 0.7.

Another characteristic of the temperature dependence of MFC below 30 K for 0.5≤x≤0.7 is the rapid decrease with decreasing T. A similar decrease in MFC is seen in otherrare-earth manganese oxides.24, 28-31) Such a rapid decrease in MFC points to spin reversal
phenomena related to rare-earth ions. The M-H curves for TmMn0.5Co0.5O3 prepared by
the solid-state reaction method showed a large high-field magnetic susceptibility evenbelow 20 K, which suggests that Tm3+ (J=6) is paramagnetic even at low temperatures.
According to Cooke et al.,29) the temperature dependence of MFC can be fitted using theequation𝐶

𝑀FC = 𝑀Mn,Co + Tm

(𝐻+𝐻int )𝑇−ΘW————————（4）where MMn,Co and Hint are the saturated moment and the internal field at the Tm sites dueto the canted Mn-Co moment, respectively. CTm is the Curie constant for paramagnetic
50

Experimental Results and Discussion

Tm3+ ions, W is the Weiss temperature, and H is the applied field, which is 250 Oe. The
solid lines in Fig. 3.6 show that the temperature dependence of the magnetization below
25 K can be well approximated using Eq. (4); the fitting parameters are listed in Table.
3.1.

Table. 3.1 Fitting parameters for MFC for x = 0.5, 0.6, and 0.7.
Co concentration x

MMn,Co / emu g-1

Hint / kOeW / K

0.5

7.8

-4.0

-11

0.6

4.0

-3.0

-14

0.7

1.8

-2.1

-13

This successful model, which is based on a ferromagnetically ordered Mn-Co
sublattice and a paramagnetic Tm sublattice, suggests that the negative internal field
induced by the Mn-Co sublattice affects the Tm sublattice. It is thought that at low
temperatures (below 25 K), the Tm3+ spin is oriented in the direction opposite to H byHint. Such spin inversion due to 3d transition metal elements and rare-earth elements
seems to be common in perovskite-type oxides with the structure ABO3, although the
crystallographic reasons why Hint acts antiferromagnetically on the rare-earth element A
are not clear.

3.1.3 Conclusion
In comparison with the plots of mass fraction vs. x (the insets of Figs. 3.2 and 3.3),
the CP method was clearly demonstrated to be more suitable than the SSR method for51

Experimental Results and Discussion

0.5<x≤0.9. Thus, we achieved the substitution of Mn through CP, and obtained almost asingle orthorhombic phase for 0.5≤x≤0.9 in TmMn1-xCoxO3.
At T > TC  58 K, TmMn1-xCoxO3, in which the Tm3+, Mn4+, Co2+, and Co3+ ions areparamagnetic, is also paramagnetic. From the data on the unit cell volume and theeffective moment, it is concluded that Co2+ has a high spin state (S=3/2) and that Co3+ in
TmMn1-xCoxO3 remains a low-spin-state ion (S=0). At T = TC, a canted magnetictransition occurs as a result of the interaction between Mn and Co, and the magnetization
increases ferromagnetically with decreasing T. Below the temperature at which MFC ismaximized, the interaction between Mn and Co ions induces a negative internal field Hint
at the Tm sites. Hint reorients the Tm3+ spin in the direction opposite to the external field
H. The total magnetization at low temperatures is explained on the basis of a twosublattice model.

3.2 Tm1-yYyMn0.2Co0.8O3
In the previous chapter, we have prepared TmMn1-xCoxO3 and investigated thephysical properties. at 0.5 ≤ x ≤ 0.7, an increase in ferromagnetic magnetization wasobserved, but no increase in ferromagnetic magnetization after x = 0.8, Therefore, in thissection, we focused on TmMn0.2Co0.8O3, the Tm site was substitution with nonmagnetic
Y, and study the influence of the change in the lattice volume by substitution of Tm1yYyMn0.2Co0.8O3 (0≤y≤0.9).

52Experimental Results and Discussion

3.2.1 Structure analysis
The Fig. 3.4 (a) and (b) is the X-ray diffraction pattern of the Tm1-yYyMn0.2Co0.8O3(0.0≤y≤0.9) series of samples prepared by the Complex Polymerization (CP) Method.

(a)Relative Intensity

y = 0.3
y = 0.2
y = 0.1

20

30

40

50

2 / degree

60

70

060
143

202
040
230
212
132 311
222
113
321
240
123 042
302
051
331
410
242
441
420

10

y = 0.0

112 220031
022
131 221

011
101
020
111

200 121002
210

y = 0.05

80(b)

Relative Intensity

y = 0.9

y = 0.7

y = 0.5

y = 0.4

10

20

30

40

50

2 / degree

60

70

80

Fig. 3.4 X-ray diffraction patterns of Tm1-yYyMn0.2Co0.8O3 (a) 0.0≤y≤0.5
and (b) 0.5≤y≤0.953Experimental Results and Discussion

Through the X-ray diffraction pattern, we can determine that all samples are
orthorhombic (space group: Pnma) single-phase structure, and all peak positions slowly
move to higher angles as the substitution element increases, and the lattice constant
impact of substitution.
Tables 3.2 ~ 3.3 are obtained by Rietveld refinement of the diffraction data of theobtained samples, a, b, and c are the lattice constants / Å in each axis direction, V is thelattice volume / Å3, x, y, z are the fractional coordinates of each atom, B is the isotropic
atom displacement parameter, S is the adaptability index (goodness of fit index) = Rwp /Re (Rwp: R-weighted mode, reliability factor of the weighted mode, Re: R expected, Rwp
in the best-fit state considering statistical error, and the analysis has almost no change
from beginning to end). Fig. 3.5 to Fig. 3.6 show the Y concentration dependence of thelattice constant and lattice volume of Tm1-yYyMn0.2Co0.8O3 (0.0≤y≤0.9) obtained from
Rietveld analysis.
In all analyses, the S value is around 1.0 to 2.0, it is considered a reliable analysis
result.

54

Experimental Results and Discussion

Fig. 3.5 Dependence of lattice constant of Tm1-yYyMn0.2Co0.8O3 (0.0≤y≤0.9) on Y
concentration.

Table. 3.2

Tm1-yYyMn0.2Co0.8O3 (0.0≤ y ≤ 0.3)

Y

0.0

0.05

0.1

0.2

0.3

V

207.8967

207.8304

207.4046

208.0710

208.1925a5.480825.479275.474035.479615.47942b

7.37633

7.37571

7.37138

7.37885

7.38069c5.14235

5.14260

5.13999

5.14604

5.14794

B(Tm)

0.6

0.682

0.575

0.185

0.313

0.682

0.575

0.185

0.313

B(Y)
B(Mn)

0.6

0.492

0.350

0.372

0.372

B(Co)

0.6

0.492

0.350

0.372

0.372

B(O1)

0.764

0.764

0.974

0.151

0.369

B(O2)

0.764

0.764

0.974

0.151

0.369

S

2.14911.86901.98401.7534

1.567355

Experimental Results and Discussion

Table. 3.3

Tm1-yYyMn0.2Co0.8O3 (0.4≤ y ≤ 0.9)

y

0.4

0.5

0.7

0.9

V

208.7452

208.7148

209.1476

209.7917a5.48228

5.481345.48091

5.48400b

7.38819

7.38733

7.39451

7.40285c5.15368

5.154415.16048

5.16764

B(Tm)

0.356

0.258

0.147

0.282

B(Y)

0.356

0.258

0.147

0.282

B(Mn)

0.372

0.372

0.372

0.101

B(Co)

0.372

0.372

0.372

0.101

B(O1)

1.328

0.164

0.164

0.164

B(O2)

0.611

0.164

0.164

0.164

S

2.19911.1633

1.33901.1637210.0
lattice volume

Unti-cell volume / Å3

209.5
209.0
208.5
208.0
207.5
207.0
0.0

0.2

0.4

0.6

0.8

1.0

Y concentration y
Fig. 3.6 Tm1-yYyMn0.2Co0.8O3 (0.0≤y≤0.9) dependence of lattice volume on Y
concentration

56

Experimental Results and Discussion

The lattice constant tended to increase slightly with increasing Y concentration. The
lattice volume tended to increase linearly with the substitution of Y, confirming thenegative pressure effect.

3.2.2 Magnetic measurement
The non-substitution of TmMn0.2Co0.8O3 (y=0.0), where almost no ferromagnetic
magnetization increase with temperature decrease.

2
y = 0.0
y = 0.05
y = 0.1

MFC / emu g

-1

1.5
1

H

=

250Oe
FC

0.5
0
-0.5

0

20

40

60

80

100

Temperature / K
Fig. 3.7 Temperature dependence of magnetization of Tm1-yYyMn0.2Co0.8O3(0.0≤y≤0.1) (cooling magnetization in magnetic field)

At y = 0.05, there was a small ups and downs behavior near 40 K, but noferromagnetic magnetization peak was shown. It is considered that the value of theinternal magnetization of the sample increased by substituting Y, but it was not so large

57

Experimental Results and Discussion

as to cancel the external magnetic field of 250 Oe and reverse the magnetization.
At y = 0.1, an increase in ferromagnetic magnetization was confirmed around 40K.
It is considered that the interaction between Mn and Co changed due to the negative
chemical pressure effect observed in the volume expansion, it induced magnetism
increased with Y substitution. In addition, after the maximum value around 40K, themagnetization was inverted to negative, and negative magnetization was observed at low
temperature.

0.5
FC
ZFC

0.4

M / emu g

-1

0.3
0.2
0.1
0

-0.1
-0.2
-0.3

0

20

40

60

80

100

Temperature / K
Fig. 3.8 Temperature dependence of magnetization of Tm0.9Y0.1Mn0.2Co0.8O3.

In Fig. 3.8, the behavior of magnetization differs between ZFC magnetization andFC magnetization at low temperatures. It is considered that the magnetization is reduced
because the Tm moment is inverted by creating details of this phenomenon will be
described later.
58

Experimental Results and Discussion

At 0.2≤y≤0.9, the peak of ferromagnetic magnetization increase at y = 0.1 tended toincrease with the increase of Y substitution. The increase in magnetization at TC ~ 60K is
due to cant magnetism.

1.5
H = 250Oe1
0.5

MFC / emu g

-1

FC

0
y = 0.2
y = 0.3
y = 0.4
y = 0.5
y = 0.7
y = 0.9

-0.5
-1

-1.5
-2

0

20

40

60

80

100

Temperature / K
Fig. 3.9 Temperature dependence of magnetization of Tm1-yYyMn0.2Co0.8O3 (0.2≤y≤0.9)(cooling magnetization in magnetic field)

Fig. 3.9 show that the Tm1-yYyMn0.2Co0.8O3 (0.2≤Y≤0.9) at the lowest temperature
has a negative value is observed within the range of 0.1≤y≤0.7. This is considered that
because the Tm moment of the negative orientation becomes so large that themagnetization is cancelled due to the transition metal elements (Mn, Co). The minimum
value of magnetization is y = 0.3. By substitution of Y, the internal magnetic field causedby the transition metals (Mn, Co) increases, and the total number of Tm moments
decreases due to the substitution of the nonmagnetic element Y.
59

Experimental Results and Discussion

Fig. 3.10 shows the fitting diagram of Tm0.9Y0.1Mn0.2Co0.8O3. The fitting showed
good agreement below about 35K. The results of this fitting are summarized in Table 3.4.

0.5
0.4

H=250 OeFC

0.3
M/emu g-1

0.2
0.1
0.0
-0.1
-0.2
-0.3

0

50

100

Temperature/K

Fig. 3.10 Temperature dependence of magnetization of Tm0.9Y0.1Mn0.2Co0.8O3.

Table. 3.4 Change of MMe (Magnetization by cant magnetism), Hint (Internal magnetic field), Θ(Weiss temperature) by fitting result
Y concentration

MMe (emu / g)Hint (Oe)Θ (K)y = 0.1

0.83553-1039.4-14.431

y = 0.3

1.4188-2637-12.901y = 0.5

1.6132-2687.7-12.248

y = 0.7

1.5038-1878.1-10.399

y = 0.9

1.6044-1188.5-10.785

By substituting Y from the fitting results, MMe shows a generally upward trend, and60

Experimental Results and Discussion

Hint tended to increase until y = 0.5 and decrease thereafter. It is thought that the decreasein magnetization at low temperature is due to the negatively oriented Tm moment, it isconsidered that the total number of Tm moments was reduced in this sample bysubstituting the non-magnetic element Y. The minimum value of magnetization at y=0.3
at the lowest temperature seems to be due to two relations between the magnitude of theinternal magnetic field and the total number of Tm moments.

Fig.3.11 Temperature dependence of inverse susceptibility Tm1-yYyMn0.2Co0.8O3(0.0≤y≤0.9).

In general, Θ has a positive value in the case of a ferromagnetic substance, and has
a negative value in many substances in an antiferromagnetic substance. Also, in the caseof paramagnetism where the interaction of magnetic atoms is very small, it showsparamagnetism at sufficiently low temperature, and χ changes according to the Curie law
with Θ = 0. Above about 70-90K. It is considered that the canted magnetic order61

Experimental Results and Discussion

developed from around this temperature to the low temperature. The Weiss temperatureΘ and the Curie constant C were obtained from the above measurement results.
Furthermore, the effective magnetic moment Peff was calculated from the formula (2).

Table. 3.5 Weiss temperature Θ and effective magnetic moment Peffof Tm1-yYyMn0.2Co0.8O3
effective magnetic

Y concentration y

Weiss temperature Θ

0.0-3.488

7.856

0.05

-2.572

7.57730.1

0.381

7.16390.3

1.612

6.58830.5

7.414

5.81230.7

15.9274.7361

0.9

32.1243.5133

moment Peff

The Weiss temperature Θ increased and the effective magnetic moment Peff
decreased with increasing y. The Weiss temperature at y = 0.0,0.05, have negative value,
become no increase in ferromagnetic magnetization, and after y = 0.1, which showed anincrease in ferromagnetic magnetization, and showed a positive value. It increased with
the increase of y. From this, it is considered that the ferromagnetic component isstrengthened by substituting Y.

3.2.3 Conclusion
The structure of Tm1-yYyMn0.2Co0.8O3 shows perovskite type orthorhombic single
phase (Pnma) is same like TmMn0.2Co0.8O3 prepared by complex polymerization. Based on
Fig. 3.4, the XRD pattern tendency for each peak to shift to a higher angle side with Y
62

Experimental Results and Discussion

substitution and the lattice volume increased with the amount of Y substitution.
As increase in magnetization due to cant magnetism was observed at TC ~ 58 K after y= 0.1, and the value of magnetization increased with Y substitution. The magnetization value
at the lowest temperature has a minimum value at y = 0.3, and a negative value at y = 0.2 to
0.7. When the external magnetic field was set to 50 Oe, the increase of the magnetization
due to the cant magnetism was observed in the sample with y = 0.05. Tm1-yYyMn0.2Co0.8O3(0.0≤y≤0.9) exhibits paramagnetism according to the Curie-Weiss law above about 80K.
The Θ increases with Y substitution and becomes positive after y = 0.1. The Peff decreases
with Y substitution, it is calculated using J or S of Tm3+, Mn4+, Co2+ (HS), Co3+ (LS) (Tm3+
is the total angular momentum J), and Mn4+, Co2+ (HS), Co3+ (LS) is the spin angularmomentum S. It is agreed with the calculated value when using S.

3.3 GdMn1-xCoxO3
As part of this research, we prepared GdMn1-xCoxO3 (0.0≤x≤1.0) in which Mn of
GdMnO3 was replaced by Co and investigated its structure and magnetism. The SSR(solid-state reaction method) was used for sample preparation, and the sample was
evaluated by X-ray diffraction measurement and magnetization measurement by MPMS.

3.3.1 Structure Analysis
The X-ray diffraction measurement results of GdMn1-xCoxO3 (0.0≤x≤1.0) are shown63

Experimental Results and Discussionin Fig. 3.12. All samples could be indexed by the orthorhombic structure (space group:Pnma), and the crystal system did not change by Co substitution. No impurities wereobserved and a single-phase sample was obtained in all products. Fig. 3.13 shows thedependence of the lattice constant and volume of GdMn1-xCoxO3 on the Co concentration.
The a-axis length decreases significantly with the increase of Co substitution. The b-axis
length increases from x = 0 ~ 0.1, but then decreases with increasing Co substitution, andthe c-axis length is almost constant but have a slightly decrease. It can be seen that theCo substitution causes the reducing lattice distortion induce by a, b, and c-axis lengths toapproach each other. The lattice volume decreases almost linearly with the increase of Co
substitution, reflecting the remarkable decrease of the a-axis length, but the lattice volume
at 0.5<x≤1.0 is decrease more obvious than that at 0≤x≤0.5. It is considered that this isdue to the change in valence of Mn ions due to Co substitution and the difference in ionicradius between Mn with Co ions. Table. 3.6 shows the ionic radii of Mn and Co ions ineach valence and spin state assuming 6-coordination 23). In addition, as reported in the Bsite substitution system of other rare earth manganese oxides25), the valence of ions in
GdMn1-xCoxO3 was determined.
valence of ions (In the expected state)range0≤x≤0.5

Gd3+

Mn3+1-2x

Mn4+x Co2+x O2-3

0.5≤x≤1.0

Gd3+

Mn4+1-x Co2+1-x

Co3+2x-1 O2-3

In this model, Mn3+ is replaced by Co2+ at 0≤x≤0.5, and in addition, Mn3+ changes to
Mn4+ to maintain electrical equilibrium, and at x=0.5, only Mn4+ and Co2+ are present.
When 0.5≤x≤1.0, the composition Co3+ replaces Mn4+ and Co2+ at the same time. The
64

Experimental Results and Discussion

average ionic radii of Mn and Co ions in each composition in this model are shown in
Table. 3.6. Above composition formula, the average ionic radii decrease with Co
substitution, especially when 0.5<x≤1.0.
x = 1.0

Relative Intensity

x = 0.9x = 0.5

122

40

50

60

x = 0.0
242
004
313
412
422

30

202
212
230
040
301
311
103
141 113321 240042 123
331
410

20

131

200
210
002 121
112
220
022

10

011
101
020
111

x = 0.370

80

2 / degree

Fig. 3.12 X-ray diffraction pattern of GdMn1-xCoxO3
235

5.9

a

230

5.7
225

5.6

V

5.5

220

3

5.4

Unit-cell volume / Å

Lattice parameters / Å

5.8

b/

215

5.3

c
210

5.2
0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

Co concentration x

Fig. 3.13 Dependence of lattice constant and lattice volume of GdMn1-xCoxO3 on Co
concentration
65

Experimental Results and Discussion

Table. 3.6 Ion radius of Mn and Co ions
Ion radii [Å]Mn3+(HS)

Mn4+

Co2+(HS)

Co3+(HS)

Co3+(LS)

0.645

0.53

0.745

0.61

0.545

Table. 3.7 Average ionic radii of Mn and Co ions in GdMn1-xCoxO3 (Co3+ assumes LS)
x

0.0

0.1

0.3

0.5

0.7

0.9

1.0

Average ion radiiof Mn, Co

0.64500.64350.64050.63750.60050.56350.5450Mn-O-Mn bond angle / degree

158
156
154
152
150
148
146

Mn-O1-Mn
Mn-O2-Mn

144
142
0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

Co concentration x
Fig. 3.14 Definition of Mn-O-Mn bond angle of GdMn1-xCoxO3 and dependence on Co
concentration

The Mn-O2-Mn bond angle in the ac plane does not change significantly and isalmost constant, but the Mn-O1-Mn bond angle in the b-axis direction tends to increase66

Experimental Results and Discussion

with Co substitution. This increase may be due to the decrease in the average ionic radiusof the B-site element due to Co substitution of Mn as shown in Table. 3.7. The decreasein the average ionic radius of the A-site element supporting the MnO6 octahedra causes
the decrease of the Mn-O-Mn bond angle as described above, whereas the decrease of theaverage ionic radius of the B-site element decreases the inclination of the MnO6 octahedra.
It may decrease and increase the Mn-O-Mn bond angle.

3.3.2 Magnetic Properties
Fig. 3.15 shows the temperature dependence of FC magnetization of GdMn1-xCoxO3(0.0≤x≤1.0). At x=0.0 and 0.1, no increase in ferromagnetic magnetization was observed,
and antiferromagnetic interaction was dominant. At x = 0.3, ferromagnetic magnetization
increases to the peak at about 67 K or less. This increase in the ferromagnetic
magnetization is considered due to the cant magnetic transition in GdMnO3, and it isassuming that increase in the ferromagnetic magnetization is caused by the increase in
the cant magnetism due to Co substitution. At lower temperatures, the magnetization
sharply decreases and shows negative magnetization below about 20K. It is thought that
this decrease in magnetization is due to antiferromagnetic coupling between the Gd
moment that contributes as paramagnetism and the canceled Mn and Co moments. At x
= 0.5, the increase in ferromagnetic magnetization is largest in this system, and after
reaching a peak at about 50 K, the magnetization decreases same like at x = 0.3, but nonegative magnetization is shown. When Co is further replaced, at x = 1.0 the increase inferromagnetic magnetization is suppressed and becomes almost non-observable. Figure.
67

Experimental Results and Discussion

3.16 shows the magnetic transition temperature analysis from the magnetization
temperature dependence of GdMn1-xCoxO3, the Weiss temperature Θ estimated from theparamagnetic susceptibility according to the Curie-Weiss law, and the Co concentration
dependence of the effective magnetic moment Peff. In addition, x = 0.0, 0.1 is thetemperature TN at which ZFC magnetization and FC magnetization are separated, and x= 0.3 to 0.9 is the temperature TC corresponding to the inflection point of FC
magnetization. x = 1.0 present almost no increase in ferromagnetic magnetization, by
fowling Curie-Weiss temperature dependence, and it is not observed separation between
ZFC magnetization and FC magnetization. The magnetic transition temperature andWeiss temperature Θ increase from x = 0.0 to 0.5, reach a maximum at x = 0.5, anddecrease with further substitution of Co. Therefore, the Co concentration dependences ofthe magnetic transition temperature and Weiss temperature suggest that Co substitution
gradually enhancement of the ferromagnetic interaction up to x = 0.5, and that weakens
the ferromagnetic interaction in substitution above x = 0.5.

68Experimental Results and Discussion

5FC
H = 250 Oe
GdMn1-xCoxO3

4

M / emu g

-1

3
2
1
0

x = 0.0
x = 0.1
x = 0.3
x = 0.5
x = 0.7
x = 0.9x = 1.0

-1
-2
-3
-4
-5
0

50

100

150

200

Temperature / K

120

9.2

100

9

80

8.8

TN, Tc

60

8.6

peff

40

8.4

20

8.2

peff /  B

Characteristic Temperature / K

Fig. 3.15 Temperature dependence of FC of GdMn1-xCoxO3 (0.0≤x≤1.0)

Θ
0

8

-20

7.8

-40

7.6
0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

Co concentration x
Fig. 3.16 Dependence of transition temperatures TN, TC, Weiss temperature Θ, effective
magnetic moment Peff on Co concentration x in GdMn1-xCoxO3 (0.0≤x≤1.0)69

Experimental Results and Discussion

The measured value of the effective magnetic moment Peff is compared with the total
orbital angular momentum J and the spin angular momentum S. It has good agreementwith the result of Pcal = g [(J (J + 1)] 1/2 and Pexp, when the total angular momentum J is
used for the effective magnetic moment of trivalent lanthanide group ions. However, theeffective magnetic moments in the ions of 3d transition metal elements do not match inthe calculation using J, and they do well when using the spin angular momentum S. From
this, it seems that there is no orbital moment, and the orbital angular momentum is frozen.
Therefore, Gd3+ is the total angular momentum J, and Mn3+, Mn4+, Co2+, and Co3+ are
spin angular momentum S was calculated value Pcal assumed composition as using
following formula. Three kinds of spin states of Co3+, high spin state HS, intermediate
spin state IS, and low spin state LS were calculated. Table 3.8 shows the effective
magnetic moment of each ion, and Fig. 3.16 shows the effective magnetic moment
calculated using Table 3.8 and the following formula and the measured value.

0≤x≤0.5𝑝cal = √(𝑝Gd )2 + (1 − 2𝑥) × (𝑝Mn3+ )2 + 𝑥 × (𝑝Mn4+ )2 + 𝑥 × (𝑝Co2+ )20.5≤x≤1.0
𝑝cal = √(𝑝Gd )2 + (1 − 𝑥) × (𝑝Mn4+ )2 + (1 − 𝑥) × (𝑝Co2+ )2 + (2𝑥 − 1) × (𝑝Co3+ )270

Experimental Results and Discussion

Table. 3.8 Effective magnetic moment in each spin state of constituent ions
g
2
2
2
2
2
2
2

Spin state
3+

Gd
Mn3+
Mn4+
Co2+
Co3+

HS
HS
HS
IS
LS

J/S
7/2
2
3/2
3/2
2
1
0

pGd, Mn, Co
7.94
4.90
3.87
3.87
4.90
2.83
0

9.5

peff / B

98.5
Co3+HS
3+

Co IS
3+

8

Co LS
exp

7.5
0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

Co concentration x

Fig. 3.17 Comparison of actual measured value of effective magnetic moment Peff andcalculated value considering the spin state of Co3+

From Fig. 3.17, the actual measured value of the effective magnetic moment Peffagrees best with when the calculated value Co3+ is assumed to be LS. Therefore, Co3+,
assumed to be contained in the sample when the Co substitution amount x is 0.6 or more,
we consider that LS having no magnetism. In addition, the decrease in magnetization andthe decrease in transition temperature on the high Co concentration side where x = 0.6 or

71

Experimental Results and Discussion

more, in the temperature dependence of magnetization can also be explained by theexistence of this low-spin Co3+. It can be seen that the measured value is lower than thecalculated value at an almost constant rate. Although the reason for this is unknown, thecomposition (0≤x≤0.5) of the sample for each Co substitution amount is assumed in thisstudy, so even when 0≤x≤0.5, a small amount of Co3+ is present, or when the sample iscalcined. There is a possibility that the compositional deviation due to the escape of Co
etc. is the cause of the low value of the effective magnetic moment.

3.3.3 Conclusion
The substitution of Mn with other transition metal elements Co, causes atransformation of Mn3+ into Mn4+. We have reconfirmed and studied about the structuraland magnetic properties of GdMn1-xCoxO3. For x = 0.3, 0.5, and 0.7, at the ordering
temperature TC the MFC showed a rapidly increase which results from canting of the Mn
and Co moments. Especially, for x = 0.3, the maximum values of MFC was observed and
MFC decreased rapidly with decreasing temperature and showed a negative magnetization
below Tcomp ~ 20 K, which is so-called a spin reversal phenomenon.

3.4 Gd1-yRyMn0.7Co0.3O3
In this work, we report the physical properties of Gd1-yRyMn0.7Co0.3O3 (R: La, Y, or
Lu, y = 0.1~0.5) to study the chemical pressure effect of the magnetic properties caused72

Experimental Results and Discussion

by non- magnetic rare- earth element substitutions. All samples were prepared by solidstate reaction method at ambient pressure.

3.4.1 Structure analysis
Figures 3.18 (a) –3.18 (c) show the XRD patterns of Gd1-yRyMn0.7Co0.3O3 samples
with substitution by the nonmagnetic elements La, Y, and Lu, respectively. These samples
are hereafter referred to as the La, Y, and Lu series, respectively. There were no impurity
phases detected, and the patterns indicated that all samples had a single phase with aperovskite-type orthorhombic structure (space group: Pnma). The lattice parameters a, b,
and c and the unit-cell volume V are shown in Table. 3.9. In the La series, b and c increase
markedly after the substitution, indicating that the unit-cell volume V greatly increases,
and the increase is about 3% when y increases from 0.0 to 0.5. On the other hand, b andc decrease in the Y and Lu series, and V decreases by about 1.3% in the Y series and by
about 2.5% in the Lu series. These changes are considered to be due to the differences in
the ionic radii of La, Y, and Lu from that of Gd. Figures 3.19(a) and 3.19(b) show a,b(b/√2), and c, and V, respectively, as functions of the average ion radius <rA> = (1-y)
rGd + yrR (La3+= 1.216 Å, Gd3+= 1.107 Å, Lu3+= 1.032 Å, and Y3+= 1.075 Å). The
parameters a, b(b/√2), and c change as functions of <rA> and appear to become closer
to each other with increasing <rA>. This indicates that Gd1-yRyMn0.7Co0.3O3 approaches
the cubic perovskite structure with increasing <rA>. On the other hand, it seems that V islinearly related to <rA> and is independent of the substituted ion. This volume change
represents the effect of chemical pressure.
73Experimental Results and Discussion(a)Relative Intensityy(La) = 0.5

y(La) = 0.3

40

50

70

202

242

30

212
040
311
141
113
321
240
123
042
331

20

y = 0.0
112
220
022
131
221

10

200210002 121

011
101
020
111

y(La) = 0.160802 / degree(b)

Relative Intensityy(Y) = 0.5

y(Y) = 0.3

30

50

60

y = 0.0
242

40

202

212
040
311
141
113
321
240
123
042
331

20

112
220
022
131
221

10

200210002 121

011
101
020
111

y(Y) = 0.1

70802 / degree(c)Relative Intensityy(Lu) = 0.5

y(Lu) = 0.3

40

50

70

202

242

30

212
040
311
141
113
321
240
123
042
331

20

y = 0.0
112
220
022
131
221

10

200210002 121

011
101
020
111

y(Lu) = 0.160802 / degree

Fig. 3.18 XRD patterns of Gd1-yRyMn0.7Co0.3O3 sample with y=0.1, 0.3, and 0.5 with
substitution with the non- magnetic elements La, Y, and Lu. (a), (b), and (c) correspond
to R=La, Y, and Lu, respectively.
74

Experimental Results and Discussion

(a)

a

𝑏/√2
c

234

(b)
Unit-cell volume / Å

3

232
230
228
226

GdMn0.7Co0.3O3
La series
Y series
Lu series

224
222
220
1.06

1.08

1.1

1.12

1.14

1.16

1.18

<rA> / ÅFig. 3.19 Average ion radius <rA> dependence of (a) lattice parameters a, b/√2, and c,and (b) unit-cell volume V.

75

Experimental Results and Discussion

Table. 3.9 Lattice parameters for the solid solutions Gd1-yRyMn0.7Co0.3O3 (R= La, Y, andLu) for y=0.1, 0.3, and 0.5. The upper, waddle, and lower values of each parameter tothe La, Y, and Lu series, respectively.
y(La)
y(Y)

0.0

0.1

0.3

0.5

5.63015.60185.57245.64295.64195.64115.6411

5.63295.6263

7.57757.6401

7.6991

7.5346

7.51757.5000

y(Lu)
a

b

c

V

5.64257.54345.3100226.01

7.53117.50187.47575.33315.37855.42435.30285.28895.27505.29695.26705.2414227.52230.19232.72225.46224.32223.17225.03222.56220.463.4.2 Magnetic properties
Figure 3.20 shows the temperature dependence of MFC. It shows a rapid increase in
MFC at TC with decreasing temperature, which results from the canting of the Mn and Co
moments. TC increases rapidly with increasing concentration y for the La series, decreases
with increasing y for the Y series, and decreases rapidly with increasing y for the Lu series.
These changes in TC correspond to the increase and decrease in the unit-cell volume V,
as shown in Fig. 3.21, where both V and TC increase almost linearly as <rA> increases.
Their linear dependence with the same slope suggests that there is a correlation between
V and TC.
The inverse magnetic susceptibility FC-1=H/MFC, shown in Figs. 3.22(a), (b) and (c)76Experimental Results and Discussion

for the La, Y, and Lu series, respectively, can be fitted above 200K using the Curie-Weisslaw (Eq. (1)).
In Fig. 3.23, we plot Peff as a function of the Co concentration y. Assuming that theelectronic states of the ions in the samples are Gd3+ [S=7/2], Mn4+ [S=3/2], Mn3+ [S=2,high spin (HS)], and Co2+ [S=3/2, HS], and there is no change in the valence on
substituting for Gd, the effective number of Bohr magnetons Pcal is estimated as:22
2
2
𝑷𝐜𝐚𝐥 = √(1 − 𝑦)𝑃Gd
3+ + 0.3𝑃Mn4+ + 0.4𝑃Mn3+ + 0.3𝑃Co2+

where 𝑃Gd3+ , 𝑃Mn4+ , 𝑃Mn3+ , and 𝑃Co2+ are 7.94, 3.87, 4.90, and 3.87, respectively. Peffand Pcal are indicated by colored symbols and the broken line in Fig. 3.23, respectively.
Peff almost corresponds to Pcal despite the elemental substitution. We considered that thesubstitution of Gd by nonmagnetic elements in this system changes the strength of theinteraction between Mn and Co without changing the valences of Mn and Co.
To explain the decrease in MFC below 40 K, the so-called spin reversal phenomenon,
we adopt the two-sublattice model used in studies of other rare-earth oxides. In this model,
the temperature dependence of MFC can be fitted using the following Eq. (4)The fitting parameters are listed in Table 3.10. The fitting results for y=0.0 and the
La series are shown by solid lines in Fig. 3.20 We assume that the decrease inmagnetization is caused by the interaction of the two magnetic sublattices, “Gd” and “Mn
and Co”, and that the Gd moment is paramagnetic. It is clear that the negative internal
field induced by the Mn and Co sublattice affects the Gd sublattice, because at low
temperatures the Gd3+ spin is oriented in the direction opposite to Hext by Hint. With
increasing concentration of the R element, 𝑀Mn, Co increases in the La series, decreases
77Experimental Results and Discussion

in the Y and Lu series, and markedly decreases in the Lu series. Hint tends to decrease
with increasing concentration of the R element in all series.

Fig. 3.20 Temperature dependence of MFC for Gd1-yRyMn0.7Co0.3O3. The broken line shows
TC for y=0.0. The solid lines for the La series are fits using Eq. (4).
234

110

GdMn0.7Co0.3O3

230

Y series

Unit-cell volume V / Å

3

La series

100
90

Lu series
228

80
226
70
224
60

222

50

220
218
1.06

1.08

1.10

1.12

1.14

1.16

Transition temperature Tc / K

232

40
1.18

<rA> / ÅFig. 3.21 V and TC as functions of <rA>. The boundary denotes the ion radius of Gd3+.
78

Experimental Results and Discussion

Fig. 3.22 Inverse magnetic susceptibility FC-1=H/MFC for (a) La series, (b) Y series, and(c) Lu series.
79Experimental Results and Discussion

The changes in MMn,Co indicate that the interaction between Mn and Co is enhanced
by increasing V and suppressed by decreasing V. From Table 3.10, we can deduce thatthe increase in Hint is caused by enhancement of the interaction between Mn and Co owing
to the increase in the maximum value of magnetization in the La series, also that the
suppression of spin reversal is caused by the reduction in the Gd concentration owing to
the substitution by non-magnetic elements.

Fig. 3.23 R concentration y dependence of effective magnetic moment Peff for Gd1yRyMn0.7Co0.3O3 (R=La, Y, Lu)

Table. 3.10 Fitting parameters for Gd1-yRyMn0.7Co0.3O3.
SamplesR
concentration y
La series
0.5
0.3
0.1
GdMn0.7Co0.3O3
0.0
Y series
0.1
0.3
0.5
Lu series
0.1
0.3
0.5

𝑀𝑀𝑛, Co /emug-1

Hint/kOe

Θ/K

17

-1.2

-9.4

8.3
6.3

-5.4
-5.6

-19
-12

6.1

-7.4

-16

5.0

-5.9

-14

3.8
3.4

-3.9
-4.0

-9.9
-15

4.3

-6.0

-15

2.1
0.38

-3.6
-0.7

-22
-36

80

Experimental Results and Discussion

3.4.3 Conclusion
The unit-cell volume V for Gd1-yRyMn0.7Co0.3O3 (R= non-magnetic rare-earth
element) shows an increase or decrease with function of the average ion radius <rA>,
which is dependent of substitutions of R. Both V and Tc parameters are linear with <rA>.
The interaction between Mn and Co is enhanced by increasing V and suppressed bydecreasing V, and the enhancement of the interaction increases the maximum value of themagnetization. The substitution of Gd with non-magnetic rare-earth element changes theunit-cell volume V, an increase of V raises the transition temperature TC, and a decreasesof V lowers TC in Gd1-yR yMn0.7Co0.3O3 system. It is considered that these chemicalpressure effects and the spin reversal phenomena occur simultaneously and produce thetemperature dependence of MFC. The R of Gd1-yYyMn0.7Co0.3O3 is not largely different
from that of GdMn0.7Co0.3O3, it is showing that the contribution of non-magnetic
substitutions Y does not significantly reduce electrical resistance.

3.5 TmMn1-xFexO3
In this section, we mainly made another experimental, attempt to replace the Mnelement with the initial perovskite manganese oxide TmMnO3 sample of TmMn1-xCoxO3,
therefore, we did not conduct an in-depth investigation. We tried to replace Mn with Fe,
and analysis the structure and magnetic properties of TmMn1-xFexO3 (x=0.1, 0.5).

81Experimental Results and Discussion

3.5.1 Structure Analysis
The sample was prepare by SSR, and mainly presents the hexagonal crystal structure，
space group is P63cm. As Fig. 3.24 shows the content of x increases as heterozygosity
increases, the Heterozygous phase was TmFeO3 and Tm2O3，space group is Pbnm. With
the increase of sintering times, the strength of Tm2O3 hetero phase peak weaken todisappears, but the intensity of TmFeO3 hetero peak has no obvious change. When thesintering temperature up to the 1400K, as Fig. 3.25 shows, the sample mainly presents
the Hexagonal crystal structure，space group is P63cm. As the content of x increases, theheterozygosity increases. Compared with the Fig. 3.24, the increase in sintering
temperature does not significantly change the structure of the sample. It is suggested that
another method (such as CP) used for prepare the sample.
TmMn1-xFexO3 sintering at 1150 K

Hexagonal (P63cm)

131

113
220
004

211
022
202

202
200

101
110
002
111

Relative intensity

Orthorhombic (Pbnm)
Tm2O3
x=0.5(2td)x=0.5(1td)

10

20

30

800

114
204 440112
106 115300
302214
116 622206
220
215 221222
117312
108

110
111
112
104 004
202 400102002

x=0.1(2td)x=0.1(1td)4050
2 /degree

60

70

80

Fig. 3.24 X-ray diffraction patterns of various samples for TmMn1-xFexO3. sintering
temperature at 1150 K.

82

Experimental Results and Discussion

TmMn1-xFexO3 sintering at 1400 K

131

113
220
004

211
022
202

202
200

20

x=0.1

104
204

30

114
204
212
115
106 300
302
214116206 220221
222215
117 312108
224
314118225
208

111 110
004
102

002

10

x=0.5

112

101
110
002
111

Relative intensity

black:Hexagonal (P63cm)
Red:orthorhombic (Pbnm)

40

50

60

70

80

2 /degree

Fig. 3.25 X-ray diffraction patterns of various samples for TmMn1-xFexO3. sintering
temperature at 1400 K.

3.5.2 Magnetic properties
Figures 3.26 and 3.27 plot, respectively, the temperature dependence of the fieldcooled (MFC) and zero-field-cooled (MZFC) magnetization for the x=0.1 and 0.5 SSR
samples. The insets of Figs. 3.26 and 3.27 respectively show the FC-1 = H/MFC for the
SSR samples above 180 K or 350K. No increase in ferromagnetic magnetization in x =0.1. At x = 0. 5, there was an anomalous behavior near 175 K, but also no ferromagnetic
magnetization peak was shown. It is considered that the MPMS machine is abnormal or
the value of the internal magnetization of the sample increased by substituting Fe, but it
was not so large as to cancel the external magnetic field of 250 Oe and reverse themagnetization. The inverse magnetic susceptibility FC-1=H/MFC for the Fe substitutions,
respectively, can be fitted in the Curie-Weiss law.

83

Experimental Results and Discussion

0.20
-1

0.9

-1

0.15

1.2

-1

FC
ZFC
FC
ZFC

1.5 TmMn0.9Fe0.1O3

4

FC=HMFc/10 emg g Oe

Long Moment/emu g-1

TmMn0.9Fe0.1O3

0.6
0.3
0.0

0.10

H=250 Oe
050

100 150 200 250 300 350
temperature/Ksintering 1400 K

H=250 Oe

0.05

sintering 1150 K
0.00

0

50

100

150

200

250

300

350

Temperature/K

Fig. 3.26 Temperature dependence of FC and ZFC magnetization of TmMn0.9Fe0.1O3.

0.35

0.6

4

-1

TmMn0.5Fe0.5O3

-1

0.25
0.20

0.4
0.2

H=250 Oe

-1

Long Moment /emu g-1

0.30

0.8
FC=HMFc/10 emg g Oe

TmMn0.5Fe0.5O3

0.0

0.15

0

sintering 1400 K

50100temperature/K

0.10

H=250 Oe

0.05
0.00

150

sintering 1150 K
0

50

100

150

Temperature /K

Fig. 3.27 Temperature dependence of FC and ZFC magnetization of TmMn0.5Fe0.5O3.

84

Summarizes

Chapter IV

Summarizes

85Summarizes

In Chapter 3, we discussed four important groups of substitutions compounds inthe RMnO3 series of samples. They are TmMn1-xCoxO3 with Co replacing Mn, and Tm1yYyMn0.2Co0.8O3 with further transition metals to substitute in Tm, and GdMn1-xCoxO3

with elements replacing Mn and Gd1-yRyMn0.7Co0.3O3 with elements replacing Ga.
First of all, we mainly focus on the impact of the preparation method on the final
molded samples. Comparing two methods, the complex polymerization method
preparation is clearly better than solid phase reaction method. We using complex
polymerization method performed the substitution of Mn with Co, and Co content x≥0.5,
the structure will change to orthorhombic single phase in TmMn1-xCoxO3 and all Y
concentration y in Tm1-yYyMn0.3Co0.7O3. And this effect is not only limited to thestructure and sample purity, but also has a profound impact on the magnetic properties.
At T > TC  58 K of TmMn1-xCoxO3, and T >TC  60K of Tm1-yYyMn0.3Co0.7O3. in which
the Tm3+, Mn4+, Co2+, and Co3+ ions are paramagnetic, corresponds Curie-Weiss law,Co2+ is considered to be high spin state (S=3/2); the Co3+ in TmMn1-xCoxO3 remains
low spin state (S=0), on the other hand, Co3+ in Tm1-yYyMn0.3Co0.7O3 seem to change
from low spin state to high spin state (S=2). At T =TC, the canted magnetic transition
due to the interaction among Mn3+, Mn4+ and Co2+ occurs, and the magnetization
increase ferromagnetically. The Mmax (which means the maximum value of themagnetization) of all Tm compound, shows interaction between Mn and Co ion inducesa negative internal field Hint at Tm site, Tm3+ is oriented toward the opposite directionof external field H by Hint.
Secondly, we discussed the relationship between chemical pressure effects and86Summarizes

compounds, the characters of this part are GdMn1-xCoxO3 and Gd1-yRyMn0.7Co0.3O3. We
first specifically analyzed physical properties of GdMn1-xCoxO3 series compounds, andfound that the substitution of Mn with other transition metal elements Co, causes atransformation of Mn3+ into Mn4+. For x = 0.3, 0.5, and 0.7, at the ordering temperature
TC the MFC showed a rapidly increase which results from canting of the Mn and Co
moments. Especially, for x = 0.3, the maximum values of MFC was observed and MFC
decreased rapidly with decreasing temperature and showed a negative magnetization
below Tcomp ~ 20 K, which is so-called a spin reversal phenomenon. So that, we have ahuge curiosity about the sample with x = 0.3, analysis of unit-cell volume V for Gd1yRyMn0.7Co0.3O3 (R= non-magnetic rare-earth element) shows an increase or decrease

with function of the average ion radius <rA> (average ion radius <rA> = (1-y) rGd + yrR),
which is dependent of substitutions of R. Both V and TC parameters are linear with <rA>.
The interaction between Mn and Co is enhanced by increasing V and suppressed bydecreasing V, and the enhancement of the interaction increases the maximum value ofthe magnetization. Meantime, the substitution of Gd with non-magnetic rare-earth
element changes the unit-cell volume V, an increase of V raises the transition
temperature TC, and a decreases of V lowers TC in Gd1-yR yMn0.7Co0.3O3 system. It isconsidered that these chemical pressure effects and the spin reversal phenomena occur
simultaneously and produce the temperature dependence of MFC.
In conclusion, the R of Gd1-yRyMn0.7Co0.3O3 is not largely different from that of
GdMn0.7Co0.3O3, it is showing that the contribution of non-magnetic substitutions Y
does not significantly reduce electrical resistance. Substitution of the R with the non87

Summarizes

magnetic elements R = La, Y, Lu for R(Mn, Co)O3(R = Gd, Tm) lead to the increase or
decrease of V, it seems that the changes in V are related to the ion radius of the rareearth as we called the chemical pressure effect.

88References

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1)

Fiebig M. Revival of the magnetoelectric effect. J Phys D Appl Phys, 2005, 38:
R123–R152

2)

Eerenstein W, Mathur N D, Scott J F. Multiferroic and magnetoelectric materials.
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3)

W. C. Röntgen, “Ueber die durch Bewegung eines im homogenen electrischen
Felde befindlichen Dielectricums hervorgerufene electrodynamische Kraft,”Annalen Der Physik, vol. 271, pp. 264–270, 1888.

4)

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92

Publications

Publications[1] Yasunori Sakatsume, JianHua Bao, Shunsuke Ohsugi, Yusuke Amakai, and Hideaki
Takano.
Effect of Co Doping on the Structure and Magnetic Properties of TmMn1-xCoxO3.
Journal of the Physical Society of Japan. Vol.87, 124704 (2018.11).
[2] JianHua Bao, Shunsuke Ohsugi, Hiroki Kunita, Yusuke Amakai, Naoki Momono,and Hideaki Takano.
Effects of Chemical Pressure on Rare-Earth Oxide GdMn0.7Co0.3O3 with
Nonmagnetic Element Substitution.
Journal of the Physical Society of Japan. Vol.89, 024703 (2020.1).

93Acknowledgments

Acknowledgments
Many people have offered me valuable help in my thesis writing, including mytutor, my classmates and my family.
Firstly, I would like to give my sincere gratitude to Prof. Takano, who withextraordinary patience and consistent encouragement, gave me great help by providing
me with necessary materials, advice of great value and inspiration of new ideas. It is
his suggestions that draw my attention to a number of deficiencies and make manythings clearer. Without his strong support, this thesis could not be the present form. My
heartfelt thanks also go to tutor. Ohsugi, for his help, I have been greatly helped inexperiments, research, and life. It is because I can more easily integrate into MuroranInstitute of Technology.
Then, I pleased to acknowledge my classmates for their invaluable assistancethroughout the preparation of the Experimental data and research results. They let me
Learn from on many helpful results and avoid many detours in writing the thesis. It isof great help for me to finish this thesis successfully.
Finally, in particular, I would like to express my wife and my parents, they gaveme great support both spiritually and materially. Without their help, it is difficult for me
to come here from China and successfully complete my studies
I would like to express my gratitude to all those who helped me during the writingof this thesis.
94