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Electron-Doping Effect on the Magnetic-Field-Sensitive
Dielectric Anomaly in CaMn1–xSbx O3
Haruka Taniguchi

1 , Hidenori Takahashi1, Akihiro Terui1 , Satoru Kobayashi1,

Michiaki Matsukawa

1 , and Ramanathan Suryanarayanan2

1 Department of Physical Science and Materials Engineering, Iwate University, Morioka 020-8551, Japan
2 ICMMO, Université Paris-Sud, 91405 Orsay, France

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We measured the temperature dependence of the dielectric constant of the electron-doped manganite CaMn1−x Sb x O3 (x = 0.1,
0.12, 0.13, 0.15, and 0.2). The real part exhibits a broad peak and the imaginary part exhibits a shoulder structure at a lower
temperature in all the samples, suggesting a gradual growth of clusters which has a dipole ordering. We newly revealed that thetemperatures of these dielectric anomalies are enhanced by more than 90 K by the Sb substitution from x = 0.1 to x = 0.2. The
result indicates that the carrier concentration should be a decisive parameter for the dipole ordering in CaMn1−x Sb x O3 . Moreover,a magnetocapacitive effect is observed in all the samples.
Index Terms— Dielectric constant, relaxor ferroelectrics.

I. I NTRODUCTION

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ANGANITES exhibit a wide variety of electronic
phases because of electron interactions [for example, the competition between ferromagnetic double exchangeinteraction and antiferromagnetic (AFM) superexchangeinteraction]. Carrier doping is one of the powerful tools
to control the electronic states. For example, an electrondoped system CaMn1−x Mo x O3 changes the ground state froma G-type AFM ordering to a charge/orbital-ordered C-type
AFM ordering [1], [2]. In another electron-doped system
Ca1−x Lax MnO3 , dielectric properties are reported [3], [4].
Moreover, in hole-doped systems such as Pr1−x Cax MnO3 andY1−x Cax MnO3 [5]–[9], the temperature dependence of thereal part of the dielectric constant exhibits a peak which issensitive to a magnetic field around the charge-ordering (CO)temperature.
Aiming to discover new phenomena in manganites,
our group has investigated an electron-doped system
CaMn1−x Sbx O3 for x ≤ 0.1 [10]–[13]. The result of X-ray
photoelectron spectroscopy indicates that the valence of Sb
is 5+ [12]. Thus, the substitution of Sb5+ ion for Mn4+site causes one-electron doping with the chemical formula
3+ 5+ 2− accompanied by a monotonic
Ca2+ Mn4+
1−2x Mn x Sb x O3
increase of unit-cell volume as a function of x. The magnetization and ac susceptibility measurements suggest a canted AFM
ordering below about 100 K [10]–[13], although the longrange order might be suppressed by the substitutional disorder.
Interestingly, a magnetization reversal is observed after a fieldcooling for 0.02 ≤ x ≤ 0.08 [10], [11]. We consider thatthe local lattice distortion of MnO6 octahedra induced by theSb substitution changes the orbital state of the eg electron of
Mn3+ and reverses the local easy axis of the magnetization.

For x = 0.05, the physical and chemical pressure effect is alsostudied [12], [13].
Just recently, we investigated the dielectric properties of
CaMn0.85 Sb0.15 O3 [14], [15], because manganites provide
interesting dielectric materials, such as multiferroics and relaxors. A broad and large peak is found in the temperaturedependence of the dielectric constant. Surprisingly, the peak issensitive to a magnetic field. One candidate for this magneticfield effect is the magnetoelectric effect in multiferroics.
Many multiferroics have been really discovered in manganites,such as YMnO3 , TbMnO3 , and MnWO4 [16]–[22]. Inhomogeneous systems, such as a relaxor Pb(Fe1/2Nb1/2 )O3 ,can be a multiferroic material as well [23]. In relaxors,
the polar nanoregions embedded in a nonpolar matrix cause alarge relative dielectric constant of about 104 [24], whereas
the homogeneous multiferroics, such as TbMnO3, usuallyexhibit   of about 10.
In this paper, in order to reveal the carrierconcentration effect on the dielectric properties of theCaMn1−x Sbx O3 system, we have newly synthesized
polycrystalline CaMn1−x Sbx O3 (x = 0.1, 0.12, 0.13,
0.15, and 0.2) and measured the dielectric constant. In all
the samples, we observed a relaxor-like broad peak in
the temperature dependence of the real part, which isfollowed by an anomaly of the imaginary part. Notably,
the characteristic temperatures of the dielectric anomalies are
remarkably enhanced by more than 90 K with increasing
the carrier concentration. This drastic change of the anomaly
temperatures indicates that the carrier concentration isa crucial parameter for the dielectric properties in the
CaMn1−x Sbx O3 system. Moreover, all the samples exhibit
a magnetocapacitive effect: the peak of the real part is
suppressed by a magnetic field of 1 T.

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Manuscript received June 15, 2018; revised August 6, 2018; accepted
August 30, 2018. Corresponding author: H. Taniguchi (e-mail: tanig@
iwate-u.ac.jp).
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TMAG.2018.2868511

II. E XPERIMENTThe polycrystalline samples of CaMn1−x Sbx O3 (x = 0.1,
0.12, 0.13, 0.15, and 0.2) were prepared by a solid-state
reaction method [14]. The stoichiometric mixtures of CaCO3 ,0018-9464 © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

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III. R ESULTS

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SrCO3 , Mn3 O4 , and Sb2 O3 powders were calcined in air at
1000 ◦ C for 48 h. The products were ground and pressed
into disk-like pellets. The pellets were sintered at 1350 ◦ C
for 48 h. We performed the X-ray diffraction measurements atroom temperature with an Ultima IV diffractometer (Rigaku)
using Cu Kα radiation.
We measured the temperature dependence of the dielectric
constant under the dc magnetic field using the parallel modeof an LC R meter (Agilent, E4980A) [14]. The samples were
cut into a parallel plate with a 3.2 × 6.0 mm2 area and a
0.7 mm thickness, and the Au wires for electric lead wereconnected by Ag paint (Dupont, 4929N). In order to improve
electric conductivity, the sample surfaces were polished to beflat using 9 μm diamond slurry, and the Ag paint was heatedat 110 ◦ C for 30 min. We performed measurements with an
ac voltage of 1 V/mm and 10, 50, or 100 kHz under 0, 0.01,
or 1 T (field cooling), obtained capacitance C and dielectricloss tanδ, and estimated the real and imaginary parts of thedielectric constant,   and   .

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Fig. 1.
(a) X-ray diffraction spectrum of CaMn1−x Sbx O3 (x = 0.1,
0.12, 0.13, 0.15, and 0.2). (b) Enlarged view around the (101) peakfor x = 0.1 and 0.2. (c) Lattice constants and unit cell volume of
CaMn1−x Sbx O3 with error bars.

number of larger Sb5+ and Mn3+ ions whose ionic radius
is 0.60 and 0.645 Å, respectively [26].
In Fig. 2(a) and (b), we compare the temperature dependence of the dielectric constant among CaMn1−x Sbx O3 (x =0.1, 0.12, 0.13, 0.15, and 0.2), which is measured undera magnetic field of 0 T and an ac voltage of 1 V/mm
and 100 kHz. We have revealed that all the samples exhibita broad peak in the real part   and a shoulder structure in
the imaginary part   . Interestingly, both of these dielectricanomalies are shifted to a higher temperature by increasing the
Sb content. The values of   and   in Fig. 2 are normalized
to be 1 at the peak temperature of   . The raw value of thereal part of the relative dielectric constant r is 103 –104 at
the peak, whereas the raw value of the imaginary part ofr drastically changes on cooling from 104 –105 to 1–102.
Except for the shoulder structure, the temperature dependenceof   seems to be roughly described by a power law. The
electrical resistivity ρ of CaMn1−x Sbx O3 is smaller thanthat of the typical insulators by several orders of magnitude,
although its temperature dependence is described by the bandgap model ρ ∝ ρ0 exp(/kB T ). Therefore, the dielectric lossof CaMn1−x Sbx O3 is expected to exhibit an extremely large
value at higher temperatures and to be suppressed remarkably
on cooling; the large values of   at higher temperatures and its
quasi-power-law temperature dependence would be originatedfrom the conduction current. Comparably large   is reallyobserved in a low resistivity system Pr1−x Cax MnO3 [27].
Therefore, we consider that the shoulder structure in   (T )is a peak appeared on a quasi-power-law background.
We estimate the characteristic temperatures of the dielectricanomalies as follows and plot them in Fig. 2(c). The temperature at which   exhibits a maximum value is defined as thepeak temperature of the real part Tp . In order to determine theshoulder temperature of   , we plot d  /d T (T ). As shown in
the inset of Fig. 2(b), the curve exhibits one minimum and one
maximum. Since the minimum of d  /d T (T ) is expected tocorrespond to the middle of the shoulder in   (T ), we define
the temperature of this minimum as the shoulder temperatureof the imaginary part Ts .
In this paper, we have newly clarified that both Tp and
Ts are almost linearly enhanced by more than 90 K
from x = 0.1 to 0.2. Notably, the drastically enhanced
Ts in the Sb substitution in CaMn1−x Sbx O3 is contrast
to the almost unchanged Ts in the Sr substitution in
Ca1−y Sr y Mn0.85Sb0.15 O3 [15].
We have also investigated the effect of the magnetic fieldon the dielectric constant of CaMn1−x Sbx O3 (x = 0.1,
0.12, 0.13, and 0.2), because we found a magnetocapacitiveeffect in CaMn0.85 Sb0.15 O3 [14], [15]. A magnetocapacitiveeffect was observed in all the samples. A magnetic field of
1 T suppresses the peak value of the real part by 3%–15%.
As an example, the result for CaMn0.88 Sb0.12 O3 is shownin Fig. 3(a). Since we have confirmed that the magnetoresistance effect of CaMn0.85 Sb0.15 O3 below 4 T is within error
margin [15], we consider that these magnetocapacitive effects
in CaMn1−x Sbx O3 are really related to the capacitive carriers.
For x = 0.1, 0.15, and 0.2, we have studied the frequency
dependence of the dielectric constant and found a common
tendency. As the result of x = 0.1 is shown in Fig. 3(b),Fig. 1(a) presents the X-ray diffraction spectrum of
CaMn1−x Sbx O3 (x = 0.1, 0.12, 0.13, 0.15, and 0.2). The
samples of x ≤ 0.15 present a Pnma orthorhombic structure,
whereas the sample of x = 0.2 is described by a P21 /m
monoclinic structure. As shown in Fig. 1(b), a new peak
appears at 23.1◦ in addition to the peak at 23.5◦ for x = 0.2.
The peak at 23.1◦ is expected to result from the (10–1)
reflection, whereas the (101) and (020) reflections are combined into one peak at 23.5◦. Therefore, the appearance ofa peak at 23.1◦ indicates a structural transition from Pnma
to P21 /m. This result is consistent with the previous study
on x = 0.1 and 0.2 [25]. The obtained lattice parameters andunit cell volume are plotted in Fig. 1(c). The values of a, b,
and c exhibit an almost linear increase with increasing the Sb
content x. This substitution effect on the lattice is reasonable:
the Sb substitution decreases the number of smaller Mn4+ ionswhose ionic radius is 0.530 Å, whereas it increases the

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Fig. 2. Temperature dependence of the dielectric constant of CaMn1−x Sbx O3 (x = 0.1, 0.12, 0.13, 0.15, and 0.2) (an ac voltage of 1 V/mm and100 kHz, 0 T). (a) Real part   . (b) Imaginary part   . The inset of (b) is the temperature dependence of d  /d T for x = 0.2. The arrow indicatesthe minimum of which temperature is defined as the shoulder temperature Ts . (c) Sb content dependence of the characteristic temperatures of thedielectric anomalies in CaMn1−x Sbx O3 , which are determined from the measurements of (a) and (b). Tp (circle) is the peak temperature of the real part,
whereas Ts (diamond) is the shoulder temperature of the imaginary part.

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ac voltage is interfered by the magnetic field. In other words,
a spontaneous dipole ordering along a certain direction isstabilized by a magnetic field.
In order to discuss the origin of the dielectric anomalies and the magnetocapacitive effect in CaMn1−x Sbx O3 ,the x − T phase diagram would be important. Focusing on the dielectric properties, we have newly revealed
that Tp and Ts are almost linearly enhanced from x =0.1 to 0.2. On other properties such as the magnetic phase,
we can speculate based on the phase diagram of the similar
carrier-doped manganites. Comparing the one-electron-doped
system CaMn1−x Sbx O3 with a two-electron-doped system
AeMn1−z Moz O3 ( Ae: Alkaline earth metal), from the viewpoint of the average valence α of Mn ions, CaMn0.85 Sb0.15 O3
with α = +3.82 and CaMn0.8 Sb0.2 O3 with α = +3.75 correspond to AeMn0.917Mo0.083 O3 and AeMn0.889Mo0.111 O3 ,respectively. Considering that the structural phase transition
from Pnma to P21 /m at the room temperature occurs
between CaMn0.85 Sb0.15 O3 and CaMn0.8 Sb0.2 O3 , the phase
diagram of CaMn1−x Sbx O3 is expected to be similar to thatof Ca0.75 Sr0.25 Mn1−z Moz O3 in which the same structuraltransition occurs between z = 0.083 and 0.111 [2]. In thephase diagram of Ca0.75 Sr0.25 Mn1−z Moz O3 , the ground statefor 0.052 ≤ z ≤ 0.111, which corresponds to 0.1 ≤ x ≤ 0.2 in
CaMn1−x Sbx O3 , is the C-type AFM phase with charge/orbital
ordering, whose ordering temperature is linearly enhancedby more than 130 K in this range. In CaMn0.85 Sb0.15 O3 ,we really observed a magnetic anomaly that suggests a COnear Tp [14], [15].
Therefore, the dielectric peak in CaMn1−x Sbx O3 , whichindicates the formation of a dipole ordering, is expected tohave a positive correlation with a charge/orbital ordering.
As for the magnetocapacitive effect, since charge/orbital orderings in CaMnO3 series stabilize a certain magnetic ordering [28], we consider that the dipole ordering related to acharge/orbital ordering is affected by a magnetic field througha magnetic ordering. This magnetic-field-sensitive dielectricpeak, which seems to be related to a charge/orbital ordering,is similar to that in the hole-doped system Pr1−x Cax MnO3 andFig. 3.
(a) Magnetocapacitive effect in the real part of the dielectric
constant   of CaMn0.88 Sb0.12 O3 (an ac voltage of 1 V/mm and 100 kHz).
(b) Frequency dependence of   of CaMn0.9 Sb0.1 O3 (0 T, 1 V/mm).
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  (T )the peak ofis suppressed and shifted to a higher
temperature with an increasing frequency.
IV. D ISCUSSION

As discussed for CaMn0.85 Sb0.15 O3 [14], [15], the peakstructure of   (T ) in CaMn1−x Sbx O3 (0.1 ≤ x ≤ 0.2)
suggests that it becomes difficult for the dipole moments tofollow the plus-minus switching of an applied ac voltage
below Tp . This behavior can be interpreted as the resultof a spontaneous dipole ordering. The large value and thebroad peak of   as well as its frequency dependence suggest that CaMn1−x Sbx O3 is a relaxor in which the polar
nanoregions exist in a non-polar matrix [24]. The inevitable
disorder induced by substitution is consistent with the relaxor
scenario. Since the shoulder structure of   (T ) is understoodas a peak appeared on a quasi-power-law background, theshoulder is expected to indicate a dielectric energy dissipation.
These results in CaMn1−x Sbx O3 (0.1 ≤ x ≤ 0.2) suggestthat local dipole-ordering clusters which start to form at
Tp expand remarkably around Ts for an energy dissipation to
be detectable in   . Since some relaxors exhibit ferroelectricity
much below the peak temperature of   (T ), it is expected tobe reasonable for dipole-ordering clusters to grow graduallyon cooling.
The suppression of the peak height of   by a magnetic fieldsuggests that the response of dipole moments to an applied

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V. C ONCLUSION

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We measured the dielectric constant of the electron-doped
manganite CaMn1−x Sbx O3 (x = 0.1, 0.12, 0.13, 0.15,
and 0.2). The temperature dependence of the real part exhibitsa broad and large peak of which value is suppressed andof which temperature is enhanced by increasing frequency,
whereas the imaginary part shows a shoulder anomaly on aquasi-power-law temperature dependence. These results suggest that CaMn1−x Sbx O3 is a relaxor: clusters with a shortrange dipole ordering appear at the peak temperature and growgradually, especially actively at the shoulder temperature.
Importantly, we have revealed that the shoulder temperatureis remarkably enhanced with the increasing Sb content x.
This result indicates that the growth of the clusters is strongly
affected by the carrier concentration. Moreover, the dielectricpeak is sensitive to a magnetic field in all the samples. By analogy with other CaMnO3 systems, a charge/orbital ordering andan accompanying magnetic ordering might play an importantrole for the dielectric ordering in CaMn1−x Sbx O3 .

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Y1−x Cax MnO3 [5]–[9], but it is the first example among
electron-doped CaMnO3 systems.
Concerning the dielectric anomaly in the imaginary
part which indicates the active development of electrically polarized regions, Ts is notably sensitive to the oneelectron-doping Sb substitution in CaMn1−x Sbx O3 , whereas
it is not affected by the isovalent Sr substituion in
Ca1−y Sr y Mn0.85 Sb0.15 O3 [15]. From these contrast results,
we emphasize that the carrier concentration is a crucial
parameter for the expansion of polar nanoregions in the
Ca1−y Sr y Mn1−x Sbx O3 system.
As a next issue, it would be important to clarify whether
macroscopic electric polarization exists at low temperatures.
In order to check our scenario on the mechanism of thedipole anomalies and the magnetocapacitive effect in the
Ca1−y Sr y Mn1−x Sbx O3 system, the magnetic ground state andthe possibility of a charge/orbital ordering should be studied.

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ACKNOWLEDGMENT

The authors would like to thank Y. Ishii, H. Yamamoto,
S. Sekigawa, and H. Kimura for their fruitful discussions. This
work was supported in part by Iwate University and in partby JSPS KAKENHI Grant Number JP17K14101.
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[3] J. L. Cohn, M. Peterca, and J. J. Neumeier, “Low-temperature permittivity of insulating perovskite manganites,” Phys. Rev. B, Condens. Matter,vol. 70, no. 21, p. 214433, 2004.
[4] J. L. Cohn, M. Peterca, and J. J. Neumeier, “Giant dielectric permittivity of electron-doped manganite thin films, Ca1−x Lax MnO3
(0 ≤x≤ 0.03),” J. Appl. Phys., vol. 97, no. 3, p. 034102, 2005.
[5] C. Jardón et al., “Experimental study of charge ordering transition in Pr0.67 Ca0.33 MnO3 ,” J. Magn. Magn. Mater., vols. 196–197,
pp. 475–476, May 1999.

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Electron-Doping Effect on the Magnetic-Field-Sensitive
Dielectric Anomaly in CaMn1–xSbx O3
Haruka Taniguchi

1 , Hidenori Takahashi1, Akihiro Terui1 , Satoru Kobayashi1,

Michiaki Matsukawa

1 , and Ramanathan Suryanarayanan2

1 Department of Physical Science and Materials Engineering, Iwate University, Morioka 020-8551, Japan
2 ICMMO, Université Paris-Sud, 91405 Orsay, France

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We measured the temperature dependence of the dielectric constant of the electron-doped manganite CaMn1−x Sb x O3 (x = 0.1,
0.12, 0.13, 0.15, and 0.2). The real part exhibits a broad peak and the imaginary part exhibits a shoulder structure at a lower
temperature in all the samples, suggesting a gradual growth of clusters which has a dipole ordering. We newly revealed that thetemperatures of these dielectric anomalies are enhanced by more than 90 K by the Sb substitution from x = 0.1 to x = 0.2. The
result indicates that the carrier concentration should be a decisive parameter for the dipole ordering in CaMn1−x Sb x O3 . Moreover,a magnetocapacitive effect is observed in all the samples.
Index Terms— Dielectric constant, relaxor ferroelectrics.

I. I NTRODUCTION

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ANGANITES exhibit a wide variety of electronic
phases because of electron interactions [for example, the competition between ferromagnetic double exchangeinteraction and antiferromagnetic (AFM) superexchangeinteraction]. Carrier doping is one of the powerful tools
to control the electronic states. For example, an electrondoped system CaMn1−x Mo x O3 changes the ground state froma G-type AFM ordering to a charge/orbital-ordered C-type
AFM ordering [1], [2]. In another electron-doped system
Ca1−x Lax MnO3 , dielectric properties are reported [3], [4].
Moreover, in hole-doped systems such as Pr1−x Cax MnO3 andY1−x Cax MnO3 [5]–[9], the temperature dependence of thereal part of the dielectric constant exhibits a peak which issensitive to a magnetic field around the charge-ordering (CO)temperature.
Aiming to discover new phenomena in manganites,
our group has investigated an electron-doped system
CaMn1−x Sb x O3 for x ≤ 0.1 [10]–[13]. The result of X-ray
photoelectron spectroscopy indicates that the valence of Sb
is 5+ [12]. Thus, the substitution of Sb5+ ion for Mn4+site causes one-electron doping with the chemical formula
3+ 5+ 2− accompanied by a monotonic
Ca2+ Mn4+
1−2x Mn x Sb x O3
increase of unit-cell volume as a function of x. The magnetization and ac susceptibility measurements suggest a canted AFM
ordering below about 100 K [10]–[13], although the longrange order might be suppressed by the substitutional disorder.
Interestingly, a magnetization reversal is observed after a fieldcooling for 0.02 ≤ x ≤ 0.08 [10], [11]. We consider thatthe local lattice distortion of MnO6 octahedra induced by theSb substitution changes the orbital state of the eg electron of
Mn3+ and reverses the local easy axis of the magnetization.

For x = 0.05, the physical and chemical pressure effect is alsostudied [12], [13].
Just recently, we investigated the dielectric properties of
CaMn0.85 Sb0.15 O3 [14], [15], because manganites provide
interesting dielectric materials, such as multiferroics and relaxors. A broad and large peak is found in the temperaturedependence of the dielectric constant. Surprisingly, the peak issensitive to a magnetic field. One candidate for this magneticfield effect is the magnetoelectric effect in multiferroics.
Many multiferroics have been really discovered in manganites,such as YMnO3 , TbMnO3 , and MnWO4 [16]–[22]. Inhomogeneous systems, such as a relaxor Pb(Fe1/2Nb1/2 )O3 ,can be a multiferroic material as well [23]. In relaxors,
the polar nanoregions embedded in a nonpolar matrix cause alarge relative dielectric constant of about 104 [24], whereas
the homogeneous multiferroics, such as TbMnO3, usuallyexhibit   of about 10.
In this paper, in order to reveal the carrierconcentration effect on the dielectric properties of theCaMn1−x Sb x O3 system, we have newly synthesized
polycrystalline CaMn1−x Sb x O3 (x = 0.1, 0.12, 0.13,
0.15, and 0.2) and measured the dielectric constant. In all
the samples, we observed a relaxor-like broad peak in
the temperature dependence of the real part, which isfollowed by an anomaly of the imaginary part. Notably,
the characteristic temperatures of the dielectric anomalies are
remarkably enhanced by more than 90 K with increasing
the carrier concentration. This drastic change of the anomaly
temperatures indicates that the carrier concentration isa crucial parameter for the dielectric properties in the
CaMn1−x Sb x O3 system. Moreover, all the samples exhibit
a magnetocapacitive effect: the peak of the real part is
suppressed by a magnetic field of 1 T.

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Manuscript received June 15, 2018; revised August 6, 2018; accepted
August 30, 2018. Corresponding author: H. Taniguchi (e-mail: tanig@
iwate-u.ac.jp).
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TMAG.2018.2868511

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The polycrystalline samples of CaMn1−x Sb x O3 (x = 0.1,
0.12, 0.13, 0.15, and 0.2) were prepared by a solid-state
reaction method [14]. The stoichiometric mixtures of CaCO3 ,75

0018-9464 © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

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III. R ESULTS

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SrCO3 , Mn3 O4 , and Sb2 O3 powders were calcined in air at
1000 ◦ C for 48 h. The products were ground and pressed
into disk-like pellets. The pellets were sintered at 1350 ◦ C
for 48 h. We performed the X-ray diffraction measurements atroom temperature with an Ultima IV diffractometer (Rigaku)
using Cu Kα radiation.
We measured the temperature dependence of the dielectric
constant under the dc magnetic field using the parallel modeof an LC R meter (Agilent, E4980A) [14]. The samples were
cut into a parallel plate with a 3.2 × 6.0 mm2 area and a
0.7 mm thickness, and the Au wires for electric lead wereconnected by Ag paint (Dupont, 4929N). In order to improve
electric conductivity, the sample surfaces were polished to beflat using 9 μm diamond slurry, and the Ag paint was heatedat 110 ◦ C for 30 min. We performed measurements with an
ac voltage of 1 V/mm and 10, 50, or 100 kHz under 0, 0.01,
or 1 T (field cooling), obtained capacitance C and dielectricloss tanδ, and estimated the real and imaginary parts of thedielectric constant,   and   .

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Fig. 1.
(a) X-ray diffraction spectrum of CaMn1−x Sbx O3 (x = 0.1,
0.12, 0.13, 0.15, and 0.2). (b) Enlarged view around the (101) peakfor x = 0.1 and 0.2. (c) Lattice constants and unit cell volume of
CaMn1−x Sbx O3 with error bars.

number of larger Sb5+ and Mn3+ ions whose ionic radius
is 0.60 and 0.645 Å, respectively [26].
In Fig. 2(a) and (b), we compare the temperature dependence of the dielectric constant among CaMn1−x Sb x O3 (x =0.1, 0.12, 0.13, 0.15, and 0.2), which is measured undera magnetic field of 0 T and an ac voltage of 1 V/mm
and 100 kHz. We have revealed that all the samples exhibita broad peak in the real part   and a shoulder structure in
the imaginary part   . Interestingly, both of these dielectricanomalies are shifted to a higher temperature by increasing the
Sb content. The values of   and   in Fig. 2 are normalized
to be 1 at the peak temperature of   . The raw value of thereal part of the relative dielectric constant r is 103 –104 at
the peak, whereas the raw value of the imaginary part ofr drastically changes on cooling from 104 –105 to 1–102.
Except for the shoulder structure, the temperature dependenceof   seems to be roughly described by a power law. The
electrical resistivity ρ of CaMn1−x Sb x O3 is smaller thanthat of the typical insulators by several orders of magnitude,
although its temperature dependence is described by the bandgap model ρ ∝ ρ0 exp(/kB T ). Therefore, the dielectric lossof CaMn1−x Sb x O3 is expected to exhibit an extremely large
value at higher temperatures and to be suppressed remarkably
on cooling; the large values of   at higher temperatures and its
quasi-power-law temperature dependence would be originatedfrom the conduction current. Comparably large   is reallyobserved in a low resistivity system Pr1−x Cax MnO3 [27].
Therefore, we consider that the shoulder structure in   (T )is a peak appeared on a quasi-power-law background.
We estimate the characteristic temperatures of the dielectricanomalies as follows and plot them in Fig. 2(c). The temperature at which   exhibits a maximum value is defined as thepeak temperature of the real part Tp . In order to determine theshoulder temperature of   , we plot d  /d T (T ). As shown in
the inset of Fig. 2(b), the curve exhibits one minimum and one
maximum. Since the minimum of d  /d T (T ) is expected tocorrespond to the middle of the shoulder in   (T ), we define
the temperature of this minimum as the shoulder temperatureof the imaginary part Ts .
In this paper, we have newly clarified that both Tp and
Ts are almost linearly enhanced by more than 90 K
from x = 0.1 to 0.2. Notably, the drastically enhanced
Ts in the Sb substitution in CaMn1−x Sb x O3 is contrast
to the almost unchanged Ts in the Sr substitution in
Ca1−y Sr y Mn0.85Sb0.15 O3 [15].
We have also investigated the effect of the magnetic fieldon the dielectric constant of CaMn1−x Sb x O3 (x = 0.1,
0.12, 0.13, and 0.2), because we found a magnetocapacitiveeffect in CaMn0.85 Sb0.15 O3 [14], [15]. A magnetocapacitiveeffect was observed in all the samples. A magnetic field of
1 T suppresses the peak value of the real part by 3%–15%.
As an example, the result for CaMn0.88 Sb0.12 O3 is shownin Fig. 3(a). Since we have confirmed that the magnetoresistance effect of CaMn0.85 Sb0.15 O3 below 4 T is within error
margin [15], we consider that these magnetocapacitive effects
in CaMn1−x Sb x O3 are really related to the capacitive carriers.
For x = 0.1, 0.15, and 0.2, we have studied the frequency
dependence of the dielectric constant and found a common
tendency. As the result of x = 0.1 is shown in Fig. 3(b),Fig. 1(a) presents the X-ray diffraction spectrum of
CaMn1−x Sb x O3 (x = 0.1, 0.12, 0.13, 0.15, and 0.2). The
samples of x ≤ 0.15 present a Pnma orthorhombic structure,
whereas the sample of x = 0.2 is described by a P21 /m
monoclinic structure. As shown in Fig. 1(b), a new peak
appears at 23.1◦ in addition to the peak at 23.5◦ for x = 0.2.
The peak at 23.1◦ is expected to result from the (10–1)
reflection, whereas the (101) and (020) reflections are combined into one peak at 23.5◦. Therefore, the appearance ofa peak at 23.1◦ indicates a structural transition from Pnma
to P21 /m. This result is consistent with the previous study
on x = 0.1 and 0.2 [25]. The obtained lattice parameters andunit cell volume are plotted in Fig. 1(c). The values of a, b,
and c exhibit an almost linear increase with increasing the Sb
content x. This substitution effect on the lattice is reasonable:
the Sb substitution decreases the number of smaller Mn4+ ionswhose ionic radius is 0.530 Å, whereas it increases the

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Fig. 2. Temperature dependence of the dielectric constant of CaMn1−x Sbx O3 (x = 0.1, 0.12, 0.13, 0.15, and 0.2) (an ac voltage of 1 V/mm and100 kHz, 0 T). (a) Real part   . (b) Imaginary part   . The inset of (b) is the temperature dependence of d  /d T for x = 0.2. The arrow indicatesthe minimum of which temperature is defined as the shoulder temperature Ts . (c) Sb content dependence of the characteristic temperatures of thedielectric anomalies in CaMn1−x Sbx O3 , which are determined from the measurements of (a) and (b). Tp (circle) is the peak temperature of the real part,
whereas Ts (diamond) is the shoulder temperature of the imaginary part.

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ac voltage is interfered by the magnetic field. In other words,
a spontaneous dipole ordering along a certain direction isstabilized by a magnetic field.
In order to discuss the origin of the dielectric anomalies and the magnetocapacitive effect in CaMn1−x Sb x O3 ,the x − T phase diagram would be important. Focusing on the dielectric properties, we have newly revealed
that Tp and Ts are almost linearly enhanced from x =0.1 to 0.2. On other properties such as the magnetic phase,
we can speculate based on the phase diagram of the similar
carrier-doped manganites. Comparing the one-electron-doped
system CaMn1−x Sb x O3 with a two-electron-doped system
AeMn1−z Moz O3 ( Ae: Alkaline earth metal), from the viewpoint of the average valence α of Mn ions, CaMn0.85 Sb0.15 O3
with α = +3.82 and CaMn0.8 Sb0.2 O3 with α = +3.75 correspond to AeMn0.917Mo0.083 O3 and AeMn0.889Mo0.111 O3 ,respectively. Considering that the structural phase transition
from Pnma to P21 /m at the room temperature occurs
between CaMn0.85 Sb0.15 O3 and CaMn0.8 Sb0.2 O3 , the phase
diagram of CaMn1−x Sb x O3 is expected to be similar to thatof Ca0.75 Sr0.25 Mn1−z Moz O3 in which the same structuraltransition occurs between z = 0.083 and 0.111 [2]. In thephase diagram of Ca0.75 Sr0.25 Mn1−z Moz O3 , the ground statefor 0.052 ≤ z ≤ 0.111, which corresponds to 0.1 ≤ x ≤ 0.2 in
CaMn1−x Sb x O3 , is the C-type AFM phase with charge/orbital
ordering, whose ordering temperature is linearly enhancedby more than 130 K in this range. In CaMn0.85 Sb0.15 O3 ,we really observed a magnetic anomaly that suggests a COnear Tp [14], [15].
Therefore, the dielectric peak in CaMn1−x Sb x O3 , whichindicates the formation of a dipole ordering, is expected tohave a positive correlation with a charge/orbital ordering.
As for the magnetocapacitive effect, since charge/orbital orderings in CaMnO3 series stabilize a certain magnetic ordering [28], we consider that the dipole ordering related to acharge/orbital ordering is affected by a magnetic field througha magnetic ordering. This magnetic-field-sensitive dielectricpeak, which seems to be related to a charge/orbital ordering,is similar to that in the hole-doped system Pr1−x Cax MnO3 andFig. 3.
(a) Magnetocapacitive effect in the real part of the dielectric
constant   of CaMn0.88 Sb0.12 O3 (an ac voltage of 1 V/mm and 100 kHz).
(b) Frequency dependence of   of CaMn0.9 Sb0.1 O3 (0 T, 1 V/mm).

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the peak of   (T ) is suppressed and shifted to a higher
temperature with an increasing frequency.

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IV. D ISCUSSION

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As discussed for CaMn0.85 Sb0.15 O3 [14], [15], the peakstructure of   (T ) in CaMn1−x Sb x O3 (0.1 ≤ x ≤ 0.2)
suggests that it becomes difficult for the dipole moments tofollow the plus-minus switching of an applied ac voltage
below Tp . This behavior can be interpreted as the resultof a spontaneous dipole ordering. The large value and thebroad peak of   as well as its frequency dependence suggest that CaMn1−x Sb x O3 is a relaxor in which the polar
nanoregions exist in a non-polar matrix [24]. The inevitable
disorder induced by substitution is consistent with the relaxor
scenario. Since the shoulder structure of   (T ) is understoodas a peak appeared on a quasi-power-law background, theshoulder is expected to indicate a dielectric energy dissipation.
These results in CaMn1−x Sb x O3 (0.1 ≤ x ≤ 0.2) suggestthat local dipole-ordering clusters which start to form at
Tp expand remarkably around Ts for an energy dissipation to
be detectable in   . Since some relaxors exhibit ferroelectricity
much below the peak temperature of   (T ), it is expected tobe reasonable for dipole-ordering clusters to grow graduallyon cooling.
The suppression of the peak height of   by a magnetic fieldsuggests that the response of dipole moments to an applied

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V. C ONCLUSION

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We measured the dielectric constant of the electron-doped
manganite CaMn1−x Sb x O3 (x = 0.1, 0.12, 0.13, 0.15,
and 0.2). The temperature dependence of the real part exhibitsa broad and large peak of which value is suppressed andof which temperature is enhanced by increasing frequency,
whereas the imaginary part shows a shoulder anomaly on aquasi-power-law temperature dependence. These results suggest that CaMn1−x Sb x O3 is a relaxor: clusters with a shortrange dipole ordering appear at the peak temperature and growgradually, especially actively at the shoulder temperature.
Importantly, we have revealed that the shoulder temperatureis remarkably enhanced with the increasing Sb content x.
This result indicates that the growth of the clusters is strongly
affected by the carrier concentration. Moreover, the dielectricpeak is sensitive to a magnetic field in all the samples. By analogy with other CaMnO3 systems, a charge/orbital ordering andan accompanying magnetic ordering might play an importantrole for the dielectric ordering in CaMn1−x Sb x O3 .

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The authors would like to thank Y. Ishii, H. Yamamoto,
S. Sekigawa, and H. Kimura for their fruitful discussions. This
work was supported in part by Iwate University and in partby JSPS KAKENHI Grant Number JP17K14101.

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Y1−x Cax MnO3 [5]–[9], but it is the first example among
electron-doped CaMnO3 systems.
Concerning the dielectric anomaly in the imaginary
part which indicates the active development of electrically polarized regions, Ts is notably sensitive to the oneelectron-doping Sb substitution in CaMn1−x Sb x O3 , whereas
it is not affected by the isovalent Sr substituion in
Ca1−y Sr y Mn0.85 Sb0.15 O3 [15]. From these contrast results,
we emphasize that the carrier concentration is a crucial
parameter for the expansion of polar nanoregions in the
Ca1−y Sr y Mn1−x Sb x O3 system.
As a next issue, it would be important to clarify whether
macroscopic electric polarization exists at low temperatures.
In order to check our scenario on the mechanism of thedipole anomalies and the magnetocapacitive effect in the
Ca1−y Sr y Mn1−x Sb x O3 system, the magnetic ground state andthe possibility of a charge/orbital ordering should be studied.

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[2] T. Okuda and Y. Fujii, “Cosubstitution effect on the magnetic, transport,
and thermoelectric properties of the electron-doped perovskite manganite
CaMnO3 ,” J. Appl. Phys., vol. 108, no. 10, p. 103702, 2010.
[3] J. L. Cohn, M. Peterca, and J. J. Neumeier, “Low-temperature permittivity of insulating perovskite manganites,” Phys. Rev. B, Condens. Matter,vol. 70, no. 21, p. 214433, 2004.
[4] J. L. Cohn, M. Peterca, and J. J. Neumeier, “Giant dielectric permittivity of electron-doped manganite thin films, Ca1−x Lax MnO3
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