PHYSICAL REVIEW B 83, 054437 (2011)

Effect of pressure on the magnetic, transport, and thermal-transport properties of theelectron-doped manganite CaMn1−x Sb x O3
Yuh Murano,1,† Michiaki Matsukawa,1,* Syuya Ohuchi,1 Satoru Kobayashi,1 Shigeki Nimori,2 Ramanathan Suryanarayanan,3Keiichi Koyama,4 and Norio Kobayashi51Department of Materials Science and Engineering, Iwate University, Morioka 020-8551, Japan
2
National Institute for Materials Science, Tsukuba 305-0047, Japan
3
Laboratoire de Physico-Chimie de L’Etat Solide, CNRS,UMR8182 Universite Paris-Sud, F-91405 Orsay, France
4
Graduate School of Science and Engineering, Kagoshima University, Kagoshima 890-0065, Japan
5
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan(Received 21 April 2010; revised manuscript received 27 January 2011; published 28 February 2011)
We have demonstrated the effect of hydrostatic pressure on magnetic and transport properties, and thermaltransport properties in the electron-doped manganite CaMn1−x Sbx O3 . The substitution of Sb5+ ion for Mn 4+ site
3+
5+of the parent matrix causes one-electron doping with the chemical formula CaMn4+
1−2x Mnx Sbx O3 accompanied
by a monotonous increase in unit-cell volume as a function of x. Upon increasing the doping level of Sb, themagnitudes of both electrical resistivity and negative Seebeck coefficient are suppressed at high temperatures,indicating the electron doping. Anomalous diamagnetic behaviors at x = 0.05 and 0.08 are clearly observed in
the field cooled dc magnetization. The effect of hydrostatic pressure on dc magnetization is in contrast to thechemical pressure effect due to Sb doping. The dynamical effect of ac magnetic susceptibility measurement
points to the formation of the magnetically frustrated clusters such as FM clusters embedded in canted AFM
matrix.
DOI: 10.1103/PhysRevB.83.054437

PACS number(s): 75.50.−y, 75.47.Gk, 62.50.−p, 72.20.Pa

I. INTRODUCTION

Manganese oxides with perovskite structure have been
extensively investigated since the discovery of the colossal
magnetoresistance (CMR) effect.1 The spontaneous insulator
to metal transition and its associated CMR effect are well
explained on the basis of the double exchange (DE) model
between Mn3+ and Mn4+ ions.2 Furthermore, the phaseseparation model, where the ferromagnetic (FM) metallic andantiferromagnetic (AFM) insulating clusters of competing
electronic phases coexist, strongly supports experimental
studies of manganites.3 The dynamic Jahn-Teller (JT) effect of
Mn3+ ions plays a crucial role in the physics of manganites.4
CaMnO3 , the end member of the Ca1−x Lax MnO3 system,
undergoes a G-type antiferromagnetic transition around TN ∼120 K accompanied by a weak ferromagnetic component,5
where each spin of Mn ions is antiparallel to its nearest neighbors of Mn. In recent years, the electron-doped
manganite system (x < 0.5)6 has attracted much attention
because of the possibility of the magnetoresistance effect.
Neutron measurements on Ca1−x Lax MnO3 7 have revealed theformation of the nanometric-scale FM clusters isolated within
a G-type AFM matrix for sufficiently low doping (x < 0.03).
Furthermore, for intermediate doping (0.03  x  0.14), a
canting of the G-type AFM structure occurs with the nanometric FM clusters. In addition to a large number of researches on
the A-site substituted electron doped manganites, it is shownthat substituting the Mn site of CaMnO3 with valence ions
3+ 5+
higher than 4+ such as CaMn4+
1−2x Mnx Mx O3 , with M = Nb,
4+
3+
Ta, V, Ru,8–13 and CaMn1−3x Mn2x Mx6+ O3 , with M = Mo,
W,8,9,14–18 creates Mn3+ ions, i.e., electrons leading to the
CMR effect. The crystallographic and magnetic properties of
the CaMn1−x Rux O3 system (x  0.1) allow us to apply thephase separated FM + AFM model to the ground state of this1098-0121/2011/83(5)/054437(13)system.10 For the CaMn1−x Mox O3 system with low doping ofMo (x = 0.04), the low temperature magnetic ground state is
better described by the canted AFM magnetic structure thanby the phase separated state.17,18 At higher doping levels of
Mo, the charge ordered state is established within the parent
matrix CaMnO3 .14 It thus is interesting to examine the physicalproperties of the Mn-site substituted compositions for our
understanding of electronic phase diagram of electron-doped
manganites.
In this paper, we demonstrate the effect of hydrostatic pressure on magnetic and transport properties, andthermal-transport properties in electron-doped manganites
CaMn1−x Sbx O3 , in order to examine a relationship between
lattice and spin. The physical pressure effect is a powerfulprobe to investigate the electronic states of manganese oxides
varying the one-electron band width at fixed doping level
because the application of external pressure gives rise to ashrinkage of Mn-O bond length and/or straightening of a
Mn-O-Mn bond angle.19 There have been several studies on
the effect of pressure on the magnetism of calcium-based
electron-doped manganites so far.20 For CaMn1−x Rux O3 withx = 0.1, the applied pressure dramatically suppresses theferromagnetic phase accompanied by a rise of the magnetictransition temperature up to ∼14 K.
In previous works of slightly electron-doped CaMnO3 with
B-site substitution, negative magnetization properties havebeen demonstrated.12,21 The negative magnetization phenomena in manganites have been originally reported in compoundswith two sublattices of Mn ions and rare-earth ions (Nd, Gd,
Dy), such as NdMnO3 ,22,23 (La,Gd)MnO3 ,24 (Nd,Ca)MnO3 ,25(Gd,Ca)MnO3 ,26 and (Dy,Ca)MnO3 .27,28 Some of these studies were discussed on the basis of ferrimagnetic scenario
leading to negative magnetization below a compensation
temperature, where Mn and some rare-earth sublattices are

054437-1©2011 American Physical Society

YUH MURANO et al.

PHYSICAL REVIEW B 83, 054437 (2011)

Polycrystalline samples of CaMn1−x Sbx O3 (x = 0.02,
0.05, 0.08, and 0.1) were prepared with a solid-state reaction
method. The stoichiometric mixtures of CaCO3 , Mn3 O4 , andSb2 O3 high-purity powders were calcined in air at 1000◦ C
for 24 h. The products were then ground and pressed intocylindrical pellets. The pellets were finally sintered at 1400 ∼
1450 ◦ C for 12 h. X-ray diffraction data revealed that all
samples are almost single phase with orthorhombic structures(P nma) (Fig. 1). The lattice parameters of the x = 0.08
sample are a = 5.326Å, b = 7.512Å, and c = 5.310Å, whichis in fair agreement with a previous work.32 The cell parameters
and unit-cell volume increase with increasing Sb doping
because the ion radius of Sb5+ (0.61Å) is greater than thevalue of Mn4+ (0.54Å). In addition, the Mn4+ ions are
replaced by Mn3+ ions (0.645Å) with one extra electron,
which contributes to the increased cell volume. The electricalresistivity was measured with a four-probe method. The
Seebeck coefficient was determined from both measurementsof a thermoelectric voltage and temperature difference along
the longitudinal direction of the measured sample. The thermal
conductivity was collected with a conventional heat-flow
method. The dc and ac magnetization measurement was
carried out using the commercial superconducting quantum
interference device (SQUID) magnetometers both at Iwate
University and National Institute for Materials Science. The ac
magnetic susceptibility measurement for x = 0.02, 0.05, and0.08 samples was measured as a function of frequency and dc
magnetic field at the ac magnetic field of 0.5 mT. In particular,
to remove the influence of the remanent magnetic field, theSQUID magnetometer with the option of a magnet resetmode was used in low-field measurements.21,33 Hydrostaticpressures in magnetization and electrical resistivity measurements were applied by using a clamp-type CuBe cell up to
1 GPa. Fluorinert was used as a pressure transmitting medium.

Intensity (arb.units)ideal

x = 0.02

x = 0.05

x = 0.08

x = 0.1

20

30

40

50
60
2θ (degree)

70

80
214

5.34
-10

5.33

a

(b)

b*

b* = b

5.32

213
2

212

c
5.31

211
5.3
210

5.29

V
209

5.28
5.27

Volume (10-30 m3)

II. EXPERIMENT(a)lattice parameters (10 m)

antiferrmagnetically coupled. Moreover, a phase separation
model between the ferromagnetic clusters and the canted AFM
matrix is proposed, in order to account for a possible origin of
the negative magnetization in manganites.22,25 In addition to
the B-site substituted manganite, the negative magnetization
was observed in some manganites without magnetic rare-earth
ions, such as LaMnO3 nano particles.29 Accordingly, thenature of the negative magnetization in manganites is oneof the crucial issues to be unveiled, which may be close toa phase-segregated state.
Furthermore, we carry out the ac magnetic susceptibility
measurements for CaMn1−x Sbx O3 , in order to examine thedynamic effect linked to magnetically frustrated properties.
For a spin-glass or cluster-glass system, a visible anomaly inthe ac susceptibility appears upon lowering T across freezing
temperature of spins or clusters when the magnetic relaxation
time becomes longer than the measuring time.30 In particular,
we believe that a phase-separated state realized in manganites
is not consistent with a typical spin-glass phase at low field.31
It thus is very intriguing to demonstrate a close relationshipbetween static and dynamic responses of magnetization to theapplied field, for our further understanding of complicatedmagnetic behavior of the present samples.

0

0.02

0.04
0.06
0.08
x (Sb content)

208
0.1

FIG. 1. (Color online) (a) X-ray diffraction patterns of
CaMn1−x Sbx O3 (x = 0.02, 0.05, 0.08, and 0.1) taken at room
temperature. Cross marks denote intensity peaks of orthorhombic
CaMnO3 . (b) The lattice parameters and unit-cell volume as a functionof Sb contents from 0.02 up to 0.1.

The magnitude of pressure was calibrated by the pressure
dependence of the critical temperature of lead. The magnetoresistance effect was measured by using a superconducting
magnet at the High Field Laboratory for Superconducting
Materials, Institute for Materials Research, Tohoku University.
III. RESULTS AND DISCUSSION
A. Effect of magnetic field and external pressure
on electrical transport

The temperature variation of electrical resistivity ρ for
the CaMn1−x Sbx O3 system is shown in Fig. 2 as a functionof the Sb content. The Sb substitution for the Mn site
up to x = 0.1 gives rise to a substantial decrease in hightemperature ρ(300 K) from 1.5 cm at the parent x = 0
sample through 0.057 cm at the lightly doped x = 0.02
sample down to 0.044 cm at the intermediately doped
x = 0.1 sample, indicating the carrier doping into the Mn
site. All samples exhibit semiconducting behaviors upondecreasing temperatures except for a metallic conduction at

054437-2

EFFECT OF PRESSURE ON THE MAGNETIC, . . .

10

TABLE I. Electrical transport characteristics of theCaMn1−x Sbx O3 series. ρ300K represents the resistivity at
300 K. W is calculated from the best fits of the high-T transport datausing the small polaron model. The MR under an applied field of
7 T and R/R under an applied pressure of 0.8 GPa are estimatedfrom the effect of magnetic field and pressure on the resistivity,
respectively. (For detail, see the captions of Figs. 2 and 3). Magnetictransition temperature Tm is estimated from the inflection point of
the field cooled M − T curve of Fig. 5(a), 5(c), and 5(e).

4x=0x = 0.02
x = 0.05
x = 0.08
x = 0.1(a)1000

ρ (Ω cm)PHYSICAL REVIEW B 83, 054437 (2011)

100
10
1
0.1
0.01
0

50

100

150

200

250

300

T (K)
0.06

Contentxρ300 K( cm)W(meV)

MR20 K(%)

R/R100 K
(%)

Tm
(K)

0
0.02
0.05
0.08
0.1

1.5
0.057
0.051
0.049
0.044

17.4
24.2
33.9
45.2

−60
−85
−64

−17
−22
−47
−43

120
110
99
88
38

(b)

ρ (Ω cm)

0.055
0.05

0.045

x=0.02x=0.05x=0.08
x=0.1

0.04
180

200

220

240 260
T (K)

0

280

300

x = 0.08

MR (%)

-20

(c)

-40

x = 0.02-60

x = 0.05

-80

20 K
-100

0

1

2

3

4

5

6

7

H (T)
FIG. 2. (Color online) (a) Temperature variation of electricalresistivity ρ for the CaMn1−x Sbx O3 system (x = 0.02, 0.05, 0.08,
and 0.1). For comparison, the data of the parent compound arepresented. (b) The ρ-T plot is magnified between 180 K and room
temperature. The solid lines denote the fits of the high-T data byusing a small polaron model. The activation energy W is listed as afunction of the Sb content in Table I. (c) Magnetoresistance effect,
MR = [R(H ) − R(0)]/R(0) × 100% at 20 K for the CaMn1−x Sbx O3
system (x = 0.02, 0.05, and 0.08).

high temperatures for the Sb light doping. The ρ-T curveof the x = 0.02 and 0.05 samples remains a metallic-likecharacter in the paramagnetic region down to ∼200 K and
250 K, respectively. On the other hand, the magnitude of

the resistivity of x = 0.08 and 0.1 is enhanced at lower
temperatures since the further doping of Sb ion breaks someof conduction paths along the Mn-O-Mn network, resulting
in a reinforcing carrier localization. In previous works,34,35
it is reported that the high-temperature transport in doped
manganites is described by a small polaron hopping model.
Now, we try to fit the resistivity data at high temperatures byusing such an expression as ρ = AT exp(W/kT ), where thefitting parameter W represents the activation energy. As listed
in Table I, with increasing Sb concentration, the value of theactivation energy shows a gradual increase from 17.4 meV at
x = 0.02 up to 45.2 meV at x = 0.1 in spite of a monotonous
suppression in the resistivity vs Sb content at high temperatures. In the following section of thermal transport, we will
discuss the transport mechanism in the CaMn1−x Sbx O3 system. We notice that the resistivity data of parent CaMnO3
observed here are, both in temperature dependence andmagnitude, similar to the ρ-T curve of the stoichiometriccomposition without oxygen defects, CaMnO3−δ (δ = 0).36
Next, let us examine the negative magnetoresistance effecton the electron-doped manganite samples with x = 0.02, 0.05,
and 0.08 as shown in Fig. 2(c). At the x = 0.05 sample, thegigantic magnetoresistance attaining −85% at 20 K under theapplied field of 7 T is observed. For the other samples, we
obtain the MR ratio of ∼ −60%. The MR data are comparable
to those reported in a previous work8 on the CaMn1−x Mx O3(M = Nb,Ta) system. These findings strongly indicate thatthe spin-polarized ferromagnetic metal clusters are establishedby the applied field and the field-induced delocalized state isrealized within the samples studied.
Finally, shown in Fig. 3 is the effect of pressure on theelectrical resistivity ρ as a function of temperature between
77 K and 300 K for the CaMn1−x Sbx O3 (x = 0.02 and 0.08).
For comparison, the data at ambient pressure are presented.
The applied pressure of 0.8 GPa on the x = 0.08 sample
suppresses the magnitude of ρ from 25% at 300 K down toabout 50% at lower temperatures around 80 K upon decreasing
temperature. The effect of pressure on the electrical transportobserved here seems to be more enhanced below the magnetictransition temperatures Tm = 110 K at x = 0.02 and 88 K at
x = 0.08, where Tm is determined from the inflection point

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YUH MURANO et al.

PHYSICAL REVIEW B 83, 054437 (2011)50

x=0.02 0GPa(a)x=0.02 0.8GPa1

x=0.02x=0.05x=0.08x=0.10(a)0

x=0.08 0GPa

S ( μ V/K)ρ (Ω cm)x=0.08 0.8GPa

-5 0

0.1

-100

100

150
200
T (K)

250

-150

300

0

0

Thermal conductivity (mW/cmK)

0300 (K)-10

x=0.02x=0.05x=0.08ΔR/R (%)

ΔR/R (%)

-40

-30
-40
-50

-100
50

100

100 (K)

-20

0

0.02

150

0.04
0.06
x (Sb content)

200

0.08

250

0.1

B. Thermal transport (Seebeck coefficient andthermal conductivity)

Seebeck coefficient S is suppressed upon increasing Sb
doping as shown in Fig. 4(a). For all samples studied, S
shows a negative value over a wide range of temperatures,strongly suggesting electron doping into the parent matrix. In
the case of the substitution of Sb5+ ion for Mn4+ site, the

250

300

-350
-400

100
80

-450

x=0

-500
-550

T

-600

N

-650
-700

60
x=0
x = 0.02
x = 0.05
x = 0.08
x = 0.140
20

0of the field cooled magnetization curve under 10 mT. The
pressure dependence of the resistance R/R (the inset of
Fig. 3) exhibits a maximum at the heavily doped sample ofx = 0.08, which is consistent with the effect of strong pressure
on the magnitude of magnetization below Tm [see Figs. 5(e)and 5(f)].

200

50

100

150
200
T (K)

250

300

TN

0

300

T (K)
FIG. 3. (Color online) (a) Temperature variation of electricalresistivity ρ for the CaMn1−x Sbx O3 system (x = 0.02 and 0.08)
at an applied pressure of 0.8 GPa. For comparison, the data atambient pressure are presented. (b) R/R = [R(T ,0.8 GPa) −R(T ,0 GPa)]/R(T ,0 GPa) ×100% for the CaMn1−x Sbx O3 system(x = 0.02, 0.05, and 0.08). The inset displays R/R as a function of
Sb content at 100 K and 300 K.

150
T(K)
-300

(b)

-20

-80

100

120

(b)

-60

50

S (μV/K)

50

50

100

150
T(K)

200

250

300

FIG. 4. (Color online) (a) Temperature variation of Seebeckcoefficient S for the CaMn1−x Sbx O3 system (x = 0.02, 0.05, 0.08,
and 0.1). The solid lines denote the T linear fits to the S(T ) data inthe temperature region above 130 K. The arrows denote the magnetictransition temperatures determined from the magnetization data.
(b) Thermal conductivity κ of CaMn1−x Sbx O3 (x = 0, 0.02, 0.05,
0.08, and 0.1). For comparison, the κ data of the parent compound
CaMnO3 are presented. The inset also represents the S data of parent
CaMnO3 .

Mn4+ ions are replaced by Mn3+ ions with one extra electron.
For lower doped samples (x = 0.02 and 0.05), the local
maximum observed in S is located near the magnetic transition
temperature as mentioned above. With further doping of Sb,
the local maximum suppressed in S of x = 0.08 is still locatedaround 130 K, but it has little relationship with the weakly
magnetic transition near 90 K. We notice a common feature in
the T -linear dependence of the Seebeck coefficient for threesamples (x = 0.02, 0.05, and 0.08) between 130 K and room
temperature, although their T dependences of the resistivity
are quite different over the same temperature range as shown054437-4

EFFECT OF PRESSURE ON THE MAGNETIC, . . .

PHYSICAL REVIEW B 83, 054437 (2011)

in Fig. 2(b). In our previous section, we demonstrated that thehigh-T resistivity is well fitted by using a small polaron model.
The corresponding expression for the Seebeck coefficient isgiven in the form ofk B ES+ S∞ ,
S(T ) =
(1)e kB T
where ES and S∞ represent the thermal activation energy andthe spin entropy in the high-temperature limit, respectively.34
In Fig. 4, we note that the 1/T law is violated at hightemperatures. The electrical resistivity of the present samples
is greatly influenced by grain boundaries in comparison to the
Seebeck measurement, giving rise to little reliable information
about the electronic states.37 In fact, such disagreements
between these transports of polycrystalline oxide materials
have been pointed out thus far.38,39
In previous works35,38 of electron-doped manganites, theT -linear dependence of S(T ) has been discussed on the basisof the conventional metal model, or Culter and Mott (CM)model. The former is given in the form of


N (E)
2 kB
kB T
+ const.
S(T ) = π
,
(2)
3e
n
E=EF
where N(E) is the density of states and n is the carrier
density.35 The latter formula for the CM model is expressed as
S(T ) = −π 2kB
∂ ln(μ0 N (E)) ∂W
kB T
−
, (3)
3e
∂E
∂E E=EF

where μ = μ0 exp(−W (E)/kB T ) is an activated mobility andW (E) is an activation energy.40 The CM model for the
random hopping system well describes a random distributionof localized states of electrons around the Fermi level. The
typical fitting parameters N(E)/n and {∂ln(μ0 N)/∂E}−1 , forthe conventional and CM models are listed in Table II. The
fitted result shows that the N (E)/n ratio is almost independentof the nominal composition. The discrepancies in the x = 0.02
and 0.05 samples between N (E)/n and n(Mn)/n(Mn3+ ) is
probably related to the fact that a single-band model is
not valid in the case of the low-carrier concentration. The
magnitudes of {∂ln(μ0 N )/∂E}−1 are similar to those of the
A-site substituted manganite Ca1−x Lax MnO3 (x = 0.017 and0.033).38 For the insulating Li1+x Ti2−x O4 sintered samples,
TABLE II. Thermal transport characteristics of theCaMn1−x Sbx O3 series. S300K represents Seebeck coefficient at
300 K. N (E)/n is calculated from the best fits of the high-T datausing the conventional model. n(Mn)/n(Mn3+ ) is the ratio of thenumber of total Mn ions to that of the Mn3+ ion. We obtain from theinverse slopes of S, {∂ln(μ0 N )/∂E}−1 , by using the CM model.
Contentx

S300K(μV/K)

0
0.02
0.05
0.08
0.1

−340
−107
−84
−63
−51

N(E)
n

 ∂ ln[μ0 N(E)] −1∂E(1/eV)n(Mn)
n(Mn3+ )

(eV)

8.2
9.3
8

50
20
12.5

0.12
0.11
0.13

it has been reported that S(T ) is proportional to temperatureand the S(T ) behavior is analyzed using the CM model.39
The Sb-substitution-induced lattice disorder influences theelectronic states of the parent matrix, causing the validity of
the CM model. Concerning the B-site substituted manganites,
there is a common trend in the temperature dependence of S(T )between CaMn1−x Wx O3 (x = 0.02 and 0.04) and the present
samples with x = 0.02, 0.05, and 0.08.16
For x = 0.1, the S(T ) data remain a nearly constant fromroom temperature down to near 100 K, then increase rapidly
and finally exhibit a positive value across the horizontal axis at
lower temperatures. Such an unusual behavior in S(T ) has beenreported both in A-site substituted system Ca1−x Smx MnO3
(x = 0.2)41 and B-site system CaMn1−x Wx O3 (x  0.07),16
indicating a holelike character of charge carriers.
Finally, let us show in Fig. 4 the temperature variationof thermal conductivity in CaMn1−x Sbx O3 (x = 0, 0.02,
0.05, 0.08, and 0.1). The thermal conduction for all samples
studied here is carried by acoustic phonons because theelectron contribution is negligible by an estimation fromthe electric resistivity data using the Wiedemann-Franz law.
Upon decreasing temperature crossing the antiferromagnetic
temperature TN , a sharp increase in κ of parent CaMnO3
is observed as reported in previous works.41,42 We believethat the thermal conductivity in the paramagnetic phase isstrongly suppressed by phonon scattering due to nanoscalestrains generated by spin correlations.42 This finding is thus
explained by a rapid reduction of the phonon scattering whenthe AFM long-range order is established below TN . The light
doping of Sb5+ strongly suppresses the magnitude of thermal
conductivity from 120 mW/cmK (50 K) at the pure x = 0
sample down to 14 mW/cmK at x = 0.02 (Fig. 4). The Sb5+
doping removes the Mn4+ ion and instead produces the Mn3+
ion for Mn sites which is the Jahn-Teller active ion with one
eg electron. It is believed that the local lattice distortion due
to the JT effect causes phonon scattering, which is close to
the depressed thermal conduction.43 In addition, the lattice
deformation due to the Sb doping with its larger ion radiusaffects the neighboring Mn3+ O6 octahedron, resulting in somevariation of the orbital state of the eg electron through the local
JT effect.
C. Effect of pressure and magnetic field on dc magnetization

Let us show in Figs. 5(a), 5(c), and 5(e) the zero-fieldcooled (ZFC) and field-cooled (FC) magnetization data of
the Sb substituted CaMn1−x Sbx O3 measured under an appliedmagnetic field of 10 mT at 0 GPa. First of all, temperaturedependent magnetization reversal appears in the FC curvesof both x = 0.05 and 0.08, as it has been reported in the
V-doped CaMn1−x Vx O3 manganites.12 However, lowering thetemperature down to 2 K, the ZFC data of both samples
show no negative value. Upon increasing the Sb content up tox = 0.1, a large difference between ZFC and FC curves is observed but such negative magnetization phenomenon vanishes.
The magnetic transition temperature Tm is suppressed from110 K at x = 0.02, through 99 K at x = 0.05, down to 38 K
at x = 0.1 due to the Sb doping because the Sb5+ ion is anonmagnetic one with the closed shell of 4d 10 . The substitutionof nonmagnetic Sb ions for Mn sites introduces electron

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YUH MURANO et al.

PHYSICAL REVIEW B 83, 054437 (2011)1

1
x=0.02
10mT

FC
ZFC

0.8

0.6

0.6

0.4

0.4

0.2

0.2

0

0

(c) 0 GPax=0.05
1.5
10 mT(d) 0.8 GPa
FC

10mT
x=0.05

ZFC

FC
ZFC

1

1.5
1

M (emu/g)

M (emu/g)x=0.0210mT

M (emu/g)

M (emu/g)

0.8 (a) 0 GPaFC(b) 0.8 GPa
ZFC
ZFC x=0

0.5

0.5

0

0
0.07

M (emu/g)

0.2

FC

0.06

10mT

0.05

x=0.1

FC
ZFC

0.04
0.03

(f) 0.8 GPa
x=0.08
10mT

0.3
FC
ZFC

0.02
0.01

ZFC

0.1

0

0.2

M (emu/g)

M (emu/g)(e) 0 GPax=0.08
0.3
10mT

0.1

0 20 40 60 80 100120 140
T (K)

0

0

-0.1

-0.1
0

20

40

60

80 100 120 140
T (K)

20

40

60

80 100 120 140
T (K)FIG. 5. (Color online) Temperature dependence of zero-field-cooled and field-cooled magnetization of the Sb substituted CaMn1−x Sbx O3
recorded at H =10 mT. In the case of ambient pressure, (a) x = 0.02, (c) x = 0.05, and (e) x = 0.08. In the case of 0.8 GPa, (b) x = 0.02,(d) x = 0.05, and (f) x = 0.08. For comparison, the ZFC data of the parent sample are given in (a). In the inset of (e), the M − T curve withthe x = 0.1 sample is presented at 0 GPa.

doping, forming ferromagnetic clusters, but destroys magnetic
ordering between Mn ions within the parent matrix.
The FC data of x = 0.08 indicates that the antiparallel
component of the canted AFM spins to the applied field is
stabilized by the Sb substitution. The spontaneously canted
magnetic moment contributing to the negative magnetization
is close to a variation of the local easy axis which is
caused by the local lattice distortion of Sb substitution incomparison to the Sb free sample. If the number of canted
spin clusters contributing to the antiparallel component isdominant over that of these clusters contributing to theparallel one along the applied field, we then obtain thenegative magnetization. Furthermore, we need to point out

the significant roles of the Dzyaloshinsky-Moriya interaction
which prefers canted spin arrangements. If the antisymmetricexchange interaction between nearest-neighbor Mn ions isdominant, such mechanism then stabilizes noncollinear spin
configuration, leading to complicated magnetic behaviors. In
order to account for the negative magnetization observed in
the lightly doped Nd1−x Cax MnO3 series, the low-temperature
spin reorientation is explained in the framework of a two-phasemodel, where the samples consist of ferromagnetic- and weakferromagnetic-phases exchange coupled at their boundaries.25
The reorientation of the magnetic moment of Nd ions inboth phases plays a crucial role on the magnetization reversal
through the f -d exchange interaction between the Nd and054437-6

EFFECT OF PRESSURE ON THE MAGNETIC, . . .

PHYSICAL REVIEW B 83, 054437 (2011)

1.2
1

1.2
x=0.02
50mT

1

ZFC
0.6

0.6

0.4

0.4

0.2

0.2

0
(c) 0 GPaFC

x=0.05
50mT

ZFC

1.5

1

M (emu/g)

M (emu/g)

0(d) 0.8 GPa
x=0.05
50mT

1.5

1
FC
ZFC

0.5

0.5

0
(e) 0 GPa0.4

x=0.0850mT0(f) 0.8 GPa
x=0.08
50mT

FC
ZFC

FC

0.4

ZFC

0.3

0.3

0.2

0.2

0.1

0.1

0

0

M (emu/g)

M (emu/g)

0.8

M (emu/g)

FC
ZFC

FC

0.8

M (emu/g)(b) 0.8 GPa

x=0.0250mT(a) 0 GPa

-0.1
0

20

40

60

80
T (K)

100 120 140

20

40

60

80 100 120 140
T (K)

-0.1

FIG. 6. (Color online) ZFC and FC magnetization curves of the Sb substituted CaMn1−x Sbx O3 (x = 0.02, 0.05, and 0.08) collected at
H = 50 mT. For ambient pressure, we get (a) x = 0.02, (c) x = 0.05, and (e) x = 0.08. For applied pressure of 0.8 GPa, (b) x = 0.02,(d) x = 0.05, and (f) x = 0.08.

manganese sublattices. It seems that the proposal model isruled out because the magnetic rare-earth ion is absent in thepresent system.
Next, we attempt to measure the effect of pressure on
the magnetization for CaMn1−x Sbx O3 , to examine a relation
between lattice distortion and spin arrangement [Figs. 5(b),5(d), and 5(f)]. The application of hydrostatic pressure up to
0.8 GPa enhances Tm by 8 ∼ 9 K at x = 0.02 and 0.05, and astable increase in Tm reaches about 5 K at the x = 0.08 sample.
We expect that a shrinkage of lattice parameters makes thesuperexchange interaction stronger between nearest-neighbort2g spins of Mn4+ ions, resulting in a stabilization of the G-type
AFM magnetic structure. The magnitude of magnetization
is not largely changed at both x = 0.02 and 0.05. On theother hand, the maximum value of the FC curve of thex = 0.08 sample is increased from 0.18 emu/g at 0 GPa up to

0.36 emu/g at 0.8 GPa, which is responsible for a sharp
increase of FM clusters. Both the ZFC and FC curves at
x = 0.02 under 0.8 GPa are, in temperature dependence,
similar to those under ambient pressure, but the magnitude of
the magnetization is suppressed by the application of pressure.
The application of external pressure on the magnetization
reversal of the x = 0.05 sample causes the positive FC curve,
approaching the ambient magnetization curve of the lowdoped sample (x = 0.02). At further Sb content of x = 0.08,
the negative magnetization of the FC curve at 0.8 GPa is limitedin the lower temperature region below ∼30 K. However, it
seems that the ZFC curves of all samples remain qualitatively
unchanged even under the applied pressure. The orthorhombic
distortion due to Sb doping is suppressed by an applicationof pressure, resulting in a similar magnetic behavior to thelower doped case under ambient pressure. At H = 50 mT, the054437-7

YUH MURANO et al.

PHYSICAL REVIEW B 83, 054437 (2011)

TABLE III. Effect of pressure on magnetic transition temperature
Tm of the CaMn1−x Sbx O3 system (x = 0.02, 0.05, and 0.08). Tm and
Tmp are determined from the inflection of M − T curves of Fig. 5pdenote aunder 0 GPa and 0.8 GPa, respectively. Mmax and Mmax
maximum in FC magnetization curves below the magnetic transition
temperatures under 0 GPa and 0.8 GPa, respectively.
and μexp
represent the Curie-Weiss temperature and the effective magnetic
moment per one manganese ion estimated from a high-temperature
linear fit of 1/M − T under ambient pressure. For comparison, theeffective magnetic moment μcal is given (for detail, see the text).

x

Tm
(K)

0
120
0.02 1100.05 990.08 88
0.1
38

p
Tmp
Mmax
Mmax
(K) (emu/g) (emu/g)

(K)

119
107
93

−119
−1
28

0.95
1.23
0.18

0.71
1.70
0.36

μexp
μcal
(μB /Mn) (μB /Mn)
3.51
3.41
3.70

3.87
3.85
3.83
3.81
3.80

3.5

(a) 1.5 T

3

ZFC x=0.02
FC x=0.02
ZFC x=0.05
FC x=0.05

M (emu/g)

2.5
2
1.5
1
0.5
0
0

50

100

150
T ( K)

200

250

300

6
(b) 5 K4

x=0.02x=0.052
M (emu/g)

negative magnetization disappears except for the lowtemperature MT curve of x = 0.08 at ambient pressure asshown in Fig. 6.
Here, we make remarks on a notable difference between
the magnetic properties of the x = 0.1 sample and other ones(x = 0.02, 0.05, and 0.08). As mentioned above, the magnetictransition temperature Tm is monotonously decreased from110 K at x = 0.02 through 99 K at x = 0.05 to 88 K at
x = 0.08 upon further Sb doping. At a maximum content of
x = 0.1, Tm is strongly depressed down to 40 K. These findings indicate that the magnetic interaction working between
manganese ions is considerably suppressed beyond x = 0.08.
For the x = 0.1 sample, the nominal content of the eg electronis taken as a maximum in all samples studied. It is true thatthe room-temperature resistivity and corresponding Seebeckcoefficient of the x = 0.1 sample exhibit their lowest values.
However, upon lowering temperatures, the suppression of themagnetic coupling working among the Mn ions around each Sb
ion probably becomes dominant over the carrier doping effectand causes a strongly reduced magnetization accompanied bya remarkable decrease of Tm . In addition to it, we point out
the giant pressure effect on the magnitude of magnetizationof the x = 0.08 sample in applied fields of 10 mT and 50 mT
as depicted in Figs. 5(d) and 6(d). In particular, the weakened
magnetic interaction due to Sb doping under ambient pressure
is strengthened under an applied pressure of 0.8 GPa, giving theremarkable increase in the magnetization by a factor of about
2. The critical content is located near x = 0.08, separating thenegative and normal magnetic tendencies.
Let us determine from the 1/M − T data taken at H =0.1 T (not shown here), the Curie-Weiss temperature and theeffective magnetic moment, for the CaMn1−x Sbx O3 system(x = 0.02, 0.05, and 0.08) as listed in Table III. The CurieWeiss temperatureis estimated from a high-temperature
linear fit of 1/M − T by using the relation χ = C/(T − ).
The Curie constant C gives the effective magnetic moment
μexp per one manganese ion. For comparison, the effective
magnetic moment μcal is calculated as a function of nominal
Sb content by using μ2eff = (1 − 2x)μ2 (Mn4+ )+xμ2 (Mn3+ ).
For free ions without the magnetic interaction, in the high-spinx=0.08

0
-2
-4
-6

-4

-2

0

2

4

Magnetic field (T)FIG. 7. (Color online) (a) Temperature dependence of ZFC andFC magnetization curves of the CaMn1−x Sbx O3 (x = 0.02 and 0.05)
samples under an applied field of 1.5 T. (b) Magnetization curves M
vs H of x = 0.02, 0.05, and 0.08 at 5 K.

configuration of Mn, μ(Mn4+ )=3.87μB and μ(Mn3+ ) =4.90μB . In the paramagnetic regime, we obtainfrom thenegative value of −119 K at x = 0.02 to the positive one of
28 K at x = 0.08, which is indicative of a variation of themagnetic interaction from antiferromagnetic to ferromagnetic
character. Furthermore, the effective magnetic moment showsa slight increase from 3.51 μB at x = 0.02 up to 3.70 μB
at x = 0.08. We suppose the valence fluctuation of the Sbion, to account for discrepancies in the effective moment
between the experimental and calculated values as listed
in Table III. In a recent study of CaMn1−x Rux O3 ,13 x-ray
absorption measurements reveal the presence of the mixed
valence states of the Ru ion. In the intermediate samples(0.1  x  0.9), it has been reported that the valence statesof Ru5+ and Ru4+ coexist with the mixed valence of Mn
ion. However, x-ray photoelectron spectroscopy analysis of
La0.9 Sb0.1 MnO3 44 indicates that the valence state of Sb ion is+5. Thus, we believe that Sb5+ exists predominantly in the
low-doping region of Sb. These differences seem to point to
the existence of ferromagnetic fluctuation or the formation of

054437-8

EFFECT OF PRESSURE ON THE MAGNETIC, . . .

PHYSICAL REVIEW B 83, 054437 (2011)-3-4

1.2x102x10(a)x=0.02
H =0.5mT-3ac(a)x=0.02

T

m

-4

-4

8x10

-4

6x10

H =0.5mT

T

ac

m

1Hz
10Hz
100Hz
1000Hz1.5x10χ"(emu/g)

χ' (emu/g)

1x10

1Hz
10Hz
100Hz
1000Hz

-4

1x10

-5

5x10

-4

4x10

(b)x=0.05-3

1.2x10H =0.5mTac(b)x=0.05

T

T

ac

m

1.2x10

1Hz
10Hz
100Hz
1000Hz

-4

1x10

-4

8x10

-5

8x10

-5

6x10

-4

6x10

-5

4x10

-4

-5

4x10

2x10

m

-4

1x10

H =0.5mT

-3

1x10

ac

-5

-4

6x10

χ"(emu/g)

1Hz
10Hz
100Hz
1000Hz8x10m

H =0.5mT

ac

-4

T

(c)x=0.08

T(c)x=0.08

χ' (emu/g)

H =0.5mT-4m

χ"(emu/g)

χ' (emu/g)

-3

1x10

1Hz
10Hz
100Hz
1000Hz

8x10

1Hz
10Hz
100Hz
1000Hz

-5

6x10

-5

4x10
-4

4x10

2x10

-4

-5

0

2x10

0

20

40

60

80
T(K)

100

120

0

140

FIG. 8. (Color online) The real part χ  of ac magnetic susceptibility of CaMn1−x Sbx O3 collected at zero dc magnetic field withfrequency ranging from 1 Hz to 1000 Hz. (a) x = 0.02, (b) x = 0.05,
and (c) x = 0.08. The amplitude of the ac magnetic field Hac was
set to be 0.5 mT. The arrows point to the direction of increasing
frequencies.

FM small clusters, in the paramagnetic phase of the Sb doped
sample above the magnetic transition temperature.
In a relatively high field of 1.5 T, the temperature variationof the magnetization for x = 0.02 and 0.05 shows no magnetic
hysteresis between the ZFC and FC curves as displayed inFig. 7(a). The M(H ) data with a small hysteresis do not saturateeven at 5 T and rise linearly with increasing H as shown

20

40

60

80
T(K)

100

120

140

FIG. 9. (Color online) The imaginary part χ  of the ac magnetic
susceptibility of CaMn1−x Sbx O3 as a function of frequency varying
from 1 Hz to 1000 Hz at Hdc = 0 T (Hac = 0.5 mT). (a) x = 0.02,(b) x = 0.05, and (c) x = 0.08.

in Fig. 7(b), indicating the AFM matrix with the small FM
region. We understand from both Figs. 2(c) and 7(b) that thelarger magnetization at high fields corresponds to the stronger
magnetoresistance effect. A linear extrapolation of the M(H )curve at 5 K to H = 0 gives a spontaneous magnetization Ms
from 0.97 emu/g at x = 0.02 through 1.2 emu/g at x = 0.05
down 0.42 emu/g at x = 0.08, revealing the existence of small
residual magnetization for all samples studied.

054437-9

YUH MURANO et al.

PHYSICAL REVIEW B 83, 054437 (2011)
-5

-4

7x10

-4

ZFC

(b) x=0.02

H =0.5mTFC

H =0.5mTac

ac

f=10Hzf=10Hz

8x10
ZFC
FC

-5

-4

5x10

4x10

-5

-4

4x10

2x10

-4

3x10

0

(d) x=0.05(c)x=0.05
H ac=0.5mT

-4

7x10

ZFC

f=10HzZFC
FC

H =0.5mT
ac

f=10Hz-5

2.5x10
-5

2x10

FC
-4

6x10

-5

1.5x10
-5

1x10

-4

5x10

-6

5x10

χ"(emu/g)

χ'(emu/g)

-5

6x10

χ"(emu/g)

χ'(emu/g)

6x10(a)x=0.02

-4

4x10

0
(f) x=0.08(e)x=0.08-4ZFC

Hac =0.5mT

f=10HzFC

f=10Hz

ac

ZFC
FC

-6

5x10

-6

4x10

-4

5x10

-6

3x10

-6

2x10

-4

4x10

-6

1x10

χ"(emu/g)

χ'(emu/g)

6x10

H =0.5mT

-4

3x10

0
-6

-4

2x10

0

20

40

60
80
T(K)

100

120

140

20

40

60

80

100 120 140

-1x10

T(K)

FIG. 10. (Color online) The real and imaginary parts of ac magnetic susceptibility of CaMn1−x Sbx O3 measured at 10 Hz under asuperimposed dc field (Hdc = 10 mT). For x = 0.02, (a) χ  and (b) χ  . For x = 0.05, (c) χ  and (d) χ  . For x = 0.08, (e) χ  and(f) χ  . The ac magnetization data are recorded as a function of temperature under ZFC and FC conditions.
D. Frequency and dc magnetic field dependences ofac magnetic susceptibility

Furthermore, we carry out the ac magnetic susceptibility
measurements for x = 0.02, 0.05, and 0.08 samples, in order
to examine the dynamic effect linked to magnetically frustrated
properties (Figs. 8 and 9). The real and imaginary parts of theac susceptibility, χ  and χ  , are registered at zero dc magnetic
field with frequency f varying from 1 Hz to 1000 Hz. For
x = 0.02, a sharp transition is noticed around Tm = 110 K,
which agrees well with the dc magnetic measurements. A
maximum of the χ  curves shows no shift in temperature withincreasing f but a second peak at lower temperature exhibits asmall shift toward high temperatures, indicating the presenceof a magnetic frustration. The magnitude of the χ  (T ) curves issuppressed with frequency over a wide range of temperatures.
In addition to the two peaks observed in χ  , a third peak inχ  appears at low frequencies, its peak then shifts towardhigher temperatures with increasing f , and finally it is mergedin the maximum of the peak at high frequencies. The newpeak around 80 K at 1 Hz strongly depends on frequency.
The finite imaginary component representing magnetic energy
dissipation is closely related to the existence of magnetic
hysteresis between the ZFC and FC dc magnetization curves.
For x = 0.05, the maximum of the peak is located at Tm =100 K, while the second one observed at a higher temperatureof 90 K is accompanied by a slight frequency shift toward low
temperatures. It seems that the frequency shift of the second
peak in the χ  and χ  curves for both x = 0.02 and 0.05
is indicative of the signature of a spin-glass-like magnetic
property. However, a substantial decrease of the peak in χ with increasing frequency is qualitatively in contrast to the
behavior of conventional spin-glass system,30 as previously
reported in phase separated Pr0.7 Ca0.3 MnO3 .31 The dynamical
effect of χ  has some relationship with the formation of themagnetically frustrated clusters such as FM clusters embedded
in canted AFM matrix. On the other hand, in the case of
x = 0.08, the second peak in the χ  and χ  curves is locatednear 55 K and it shows a weak frequency dependence as054437-10

EFFECT OF PRESSURE ON THE MAGNETIC, . . .

PHYSICAL REVIEW B 83, 054437 (2011)-4

5.5x10(a)x=0.1-4

5x10

H =0.5mT

1Hz
10Hz
100Hz
1000Hzac-4

χ' (emu/g)

4.5x10

-4

4x10

-4

3.5x10

-4

3x10

-4

2.5x10(b)x=0.1-5

1.2x10

1Hz
10Hz
100Hz
1000HzH =0.5mTac-5χ"(emu/g)

1x10

-6

8x10

-6

6x10

-6

4x10

-6

2x10

0

(c) x=0.1

-4

5x10

-5

H =0.5mT

ZFC
FC

ac

f=10Hz

-4

ZFC
FC

-4

4x10

-5

1x10

-6

8x10

-4

-6

3.5x10

6x10

-4

-6

3x10

4x10

-4

χ"(emu/g)

χ' (emu/g)

4.5x101.2x10-6

2.5x10

2x10

-4

2x10

0

20

40

60

80

0

100

T(K)

FIG. 11. (Color online) The real and imaginary parts of ac
magnetic susceptibility of CaMn0.9 Sb0.1 O3 a function of frequency
varying from 1 Hz to 1000 Hz at Hdc = 0 T (Hac = 0.5 mT). For
x = 0.1, (a) χ  and (b) χ  . For comparison, the ac magnetization data
recorded as a function of temperature under ZFC and FC conditions
are given in (c) (Hdc = 10 mT).

shown in Figs. 8 and 9. We notice that the second peaksof x = 0.02 and 0.05 are located around 47 K and 90 K,
respectively, corresponding to the maximum of the ZFC dc
magnetization. However, the second peak of x = 0.08 has nocorresponding maximum in the ZFC dc curve [Fig. 5(c)]. We
note that the ac susceptibility of the parent CaMnO3 exhibits
no magnetic peak except for a peak associated with long-range
magnetic ordering.35 Moreover, for the B-site substituted
CaMn1−x Mox O3 (x = 0.04), the imaginary part χ  shows
only a sharp peak at 105 K around the magnetic transition
temperature and no signal at low temperatures.18 For the
low-doped CaMn1−x Rux O3 (x = 0.06), both χ  and χ  exhibit
neither frequency dependence nor an enhanced peak below
Tm .10 This finding predicts that the low-temperature groundstate of the light Ru substituted CaMnO3 is better explainedby the complex canted magnetic structure than by the phaseseparated model. For A-site substituted Ca0.9 La0.1 MnO3 , amuch larger hysteresis in the dc magnetization between ZFC
and FC curves, and the frequency effect on the ac susceptibility
demonstrate that its low-temperature state is considered as acluster glass one without long-range ferromagnetism.35
Now, under zero-field-cooled and field-cooled conditions,
we display in Fig. 10 the ac susceptibility measurements ofx = 0.02, 0.05, and 0.08 with a superimposed dc field (Hdc =10 mT). First of all, the sharp peaks in both χ  and χ  aroundTm in the absence of dc field are strongly suppressed under
the presence of the dc field but the second peaks of x = 0.02
and 0.05 still remain stable. The collapse of the steep peakat zero dc field is caused by the application of low dc field
since the applied low field strongly suppresses the magnetic
fluctuation associated with the magnetic transition.45 Next, amagnetic divergence in the ac magnetization between the ZFC
and FC curves is visible at x = 0.02, but upon increasing the
Sb content, both the ZFC and FC ac curves at x = 0.08 become
reversible and exhibit no clear differences except for the hightemperature region near Tm . Finally, for the x = 0.08 sample
the maximum of the peak in FC χ  of Fig. 10(a) is observed
around 85 K, at the temperature where the FC dc curve reaches
a maximum as shown in Fig. 5(e). If we assume that thepeak in FC χ  is related to the formation of magneticallyfrustrated clusters associated with a phase-separated state, wecannot identify the second peak with corresponding signaturein the dc magnetization curve. However, the anomalous peakis located near the characteristic temperature pointing to thedc magnetization reversal. Accordingly, we suppose that theexistence of the anomalous peak in χ  of x = 0.08 hassome relationship with the negative magnetization phenomena
observed here. For comparison, the ac susceptibility data ofthe x = 0.1 sample are presented in Fig. 11. We notice thefrequency dependence of the ac peak in both χ  and χ  around40 K corresponding to the ZFC dc peak in the inset of Fig. 5(e),indicating the strong evidence for a magnetically frustrated
state.
IV. SUMMARY

We have demonstrated the effect of hydrostatic pressure
on magnetic and transport properties of the electron-doped
manganite CaMn1−x Sbx O3 . In addition, thermal transport
properties (Seebeck coefficient and thermal conductivity)of the CaMn1−x Sbx O3 system have been examined as afunction of T . Furthermore, the ac magnetic susceptibility
measurements for x = 0.02, 0.05, and 0.08 samples have been
performed, in order to examine a close relation between the
dynamic effect linked to magnetically frustrated properties andthe static dc magnetization.
The substitution of the Sb5+ ion for Mn 4+ site of the parent
matrix causes one-electron doping with the chemical formula3+
5+
CaMn4+
1−2x Mnx Sbx O3 accompanied by a monotonous increase in unit-cell volume as a function of x. Upon increasing
the doping level of Sb, the magnitudes of both electricalresistivity and the Seebeck coefficient are suppressed at hightemperatures, indicating the electron doping. The CM model
applied to the random hopping system gives a better fit to the
Seebeck coefficient at higher temperatures. The light doping

054437-11

YUH MURANO et al.

PHYSICAL REVIEW B 83, 054437 (2011)of Sb5+ strongly suppresses the high-thermal conductivity ofthe parent sample through the local lattice distortions.
The anomalously diamagnetic behaviors at x = 0.05 and0.08 are clearly observed in the field-cooled dc magnetization.
The magnetization curves of x = 0.05 and 0.08 under anapplied pressure of 0.8 GPa exhibit similar behaviors to
those of the x = 0.02 and 0.05 samples without pressure,respectively. We expect that these findings are close to somechange of the local easy axis of magnetization due to the local
lattice distortion induced by the Sb doping, in comparison
to the case of the A-site substitution. A notable differencein the magnetization curves between the x = 0.1 sample andother ones is attributed to the weakened magnetic interaction
working among the Mn ions around the Sb ion.

The dynamical effect of the ac magnetic susceptibility
measurement has some relationship with the formation of themagnetically frustrated clusters such as FM clusters embedded
in canted AFM matrix. In particular, we suppose that theanomalous peak in FC χ  of x = 0.08 is related to the negative
magnetization observed here, suggesting the metastable andnonequilibrium nature of the above effect.

*20

matsukawa@iwate-u.ac.jp
Present address: DOWA Electronics Materials Co., Ltd., Okayama
702-8045, Japan1
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C. Zener, Phys. Rev. 82, 403 (1951); P. G. deGennes, ibid. 118,
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B. Raveau, Y. M. Zhao, C. Martin, M. Hervieu, and A. Maignan,
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A. I. Shames, E. Rozenberg, C. Martin, A. Maignan, B. Raveau,
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Y. Guo, W. Li, S. Roy, and N. Ali, Chem. Mater. 17, 2735 (2005).
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R. Ang, Y. P. Sun, Y. Q. Ma, B. C. Zhao, X. B. Zhu, and W. H.
Song, J. Appl. Phys. 100, 063902 (2006).
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Q. Zhou, B. J. Kennedy, Z. Zhang, L. Y. Jang, and J. B. Aitken,
Chem. Mater. 21, 4203 (2009).
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ACKNOWLEDGMENTS

This work was partially supported by a Grant-in-Aid for
Scientific Research from Japan Society of the Promotion of
Science.

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PHYSICAL REVIEW B 83, 054437 (2011)

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