PHYSICAL REVIEW B 67, 104433 共2003兲

Anisotropic phonon conduction and lattice distortions in colossal-magnetoresistance bilayer
manganite „La1Àz Prz … 1.2Sr1.8Mn2 O7 „zÄ0, 0.2, 0.4, and 0.6… single crystals
M. Matsukawa, M. Narita, T. Nishimura, and M. Yoshizawa
Department of Materials Science and Technology, Iwate University, Morioka 020-8551, Japan

M. Apostu, R. Suryanarayanan, and A. Revcolevschi
Laboratoire de Physico-Chimie de L’etat Solide, CNRS, UMR 8648 Universite Paris-Sud, 91405 Orsay, France

K. ItohNational Institute for Materials Science, Tsukuba 305-0003, Japan

N. Kobayashi
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
共Received 3 June 2002; revised manuscript received 9 December 2002; published 31 March 2003兲
We have undertaken a systematic study of thermal conductivity as a function of temperature and magnetic
field of single crystals of the compound (La1⫺z Prz ) 1.2Sr1.8Mn2 O7 for z(Pr)⫽0.2,0.4, and 0.6. The lattice
distortion due to Pr substitution and anisotropic thermal conductivity in bilayer manganites are discussed on
the basis of different relaxation models of local lattice distortions in metal and insulating states proposed byMedarde et al. The giant magnetothermal effect is scaled as a function of magnetization and discussed on thebasis of a systematic variation of the occupation of the e g -electron orbital states due to Pr substitution.
DOI: 10.1103/PhysRevB.67.104433

PACS number共s兲: 63.90.⫹t, 72.15.Gd

I. INTRODUCTION

consequences on the physical properties. Let us note that the
optimally hole-doped compound La1.2Sr1.2Mn2 O7 (x⫽0.4)
exhibits a CMR of more than 98% near the paramagnetic
insulator 共PI兲 to ferromagnetic metal 共FM兲 transition temperature T c ⫽⬃120 K. 9 The thermal conductivity measurements of the double-layer manganite, La1.2Sr1.2Mn2 O7 werereported recently indicating an enhanced giant magnetothermal effect due to its layered structure.10 For the end memberx⫽0 LaMnO3 , which is a cubic compound with JT distortions, it was reported that the value of ␬ measured on a
stoichiometric single crystal corresponds to a thermally good
conductor, such as an ideal phonon gas.11 On the other hand,the end member x⫽1 compound CaMnO3 , without JT active
Mn sites, shows a higher thermal conduction in comparison
to the low-␬ data obtained for the hole-doped compounds.8
Therefore, it is desirable to examine the close relationshipexisting between the lattice distortion and thermal conductivity in layered manganites.
In this paper, we report a systematic study of thermal
conductivity as a function of temperature and magnetic fieldof single crystals of the compound (La1⫺z Prz ) 1.2Sr1.8Mn2 O7 ,for z(Pr)⫽0.2,0.4, and 0.6. Keeping the hole doping fixed atx⫽0.4, the chemical pressure effect due to substitution of Pr
on La-ion sites enhances anisotropic lattice parameters12,13
and results in a variation of the e g -electron character, as reported in 共Ref. 14兲. The lattice distortion due to Pr substitution and the anisotropic thermal conductivity in bilayer manganites were discussed on the basis of different relaxation
models of local lattice distortions in metal and insulatingstates proposed by Medarde et al.15 Next, the giant magnetothermal resistivity was scaled as a function of magnetization and discussed on the basis of a systematic variation ine g -electron orbital states.

Since the discovery of colossal magnetoresistance 共CMR兲
in the hole-doped perovskite manganites Ln1⫺x Dx MnO3
(Ln⫽ trivalent rare earth; D⫽ divalent alkaline earth Ca, Sr,
Ba, Pb兲, extensive studies of the field-induced complex physics exhibited by these CMR compounds have been reported.1
Though the double-exchange 共DE兲 mechanism2 plays a major role in explaining some of the properties, a quantitativemodel to account for the insulator-metal transition and the
CMR effect is yet to be proposed. In the DE model, thecarriers are strongly ferromagnetically coupled, due toHund’s rule coupling, to the Mn core which also results in
the hopping of electrons between the Mn ions. However, it
was pointed out that the coupling of carriers to local JahnTeller共JT兲 distortions and to the Mn spins must also be
considered.3 Further, several recent experiments seem to support the phase-separation model.4 Thermal transport measurements provide additional crucial information on the various scattering mechanisms of thermal carriers such as
electrons and phonons and are expected to improve the understanding of some of the phenomena encountered in the
manganites. There have been relatively few reports5– 8 onthermal transport in cubic manganites. The thermal conductivity of cubic manganites has been discussed on the basis ofstatic and dynamic lattice distortions by several authors. It
should be noted that the Ln1⫺x D x MnO3 cubic perovskite
compounds belong to the Ruddlesden-Popper series generally described as (Ln,D) n⫹1 Mnn O3n⫹1 with n⫽⬁. For n⫽2, one obtains the bilayer Mn perovskite (Ln,D) 3 Mn2 O7 ,in which two MnO2 layers are stacked with (Ln,D) 2 O2 layers along the c axis of the structure. The reduced dimensionality of these compounds has been shown to have interesting0163-1829/2003/67共10兲/104433共6兲/$20.00

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M. MATSUKAWA et al.
II. EXPERIMENT

Single crystals of (La1⫺z Prz ) 1.2Sr1.8Mn2 O7 (z⫽0, 0.2,
0.4, and 0.6兲 were grown from sintered rods of the same
nominal composition by the floating-zone method, using amirror furnace. Crystals could be easily cleaved to yieldshiny surfaces. X-ray Laue patterns have indicated thecleaved surface to be along the ab plane of the structure andtherefore the c axis perpendicular to it. An x-ray powder
pattern taken on a small part of the cleaved crystal did notindicate the presence of any additional phases. The calculated lattice parameters are listed in Refs. 12 and 13. The Pr
substitution at La ion sites resulted in a small contraction of
the a-axis parameter and an expansion of the c axis parameter. Energy-dispersive x-ray analyses of the cleaved surface
revealed the compositions of the two samples to be close to
those of the respective sintered rods. The dimensions of thecrystals used in the experiments reported here were typically
3.4⫻2.8 mm2 in the ab plane and 1.0 mm along the c axis.
The end member compound Sr3 Mn2 O7 was prepared by apowder sintering technique under the annealing condition
1650°C for 12 h first reported by Mizutani et al.16 and by
Mitchell et al.17 After rapidly cooling it down to room temperatures to prevent decomposition, the polycrystalline
sample was postannealed at 400°C for 24 h to remove its
oxygen deficiency. The dimensions of the cylindrical sinteredsample used in the thermal measurement were 4.4 mm indiameter and 8 mm along the longitudinal direction. The
x-ray powder pattern of this sample showed that the sample
obtained consists mainly of a single phase with the 327 crystal structure. The magnetization measurements also revealed
that the present sample shows an antiferromagnetic transition
around T N ⯝160 K. 17 The thermal conductivity, both in theab plane and along the c axis of the crystal, was measured
by means of the steady-state heat-flow method using a
Gifford-McMahon type cryocooler in zero field. Magnetothermal conductivity measurements were carried out at the
National Research Institute for Metals and at the High Field
Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. The resistivity in the abplane of the crystal was measured using a conventional fourprobe technique. The zero-field-cooled magnetization measurements were made by superconducting quantum interference device using a magnetometer both at Iwate University
and in Orsay.
III. RESULTS AND DISCUSSION

Figures 1共a兲 and 1共b兲 present the ab plane normalized
resistivity ␳ ab and the ab plane magnetization M ab of oursamples (z⫽0, 0.2, 0.4, and 0.6兲 as a function of temperature. The ␳ data of the polycrystalline sample Sr3 Mn2 O7 arealso shown in the inset of Fig. 1 共a兲. For the z⫽0 crystal, thevalue of ␳ ab dropped sharply at ⬃120 K, close to the insulating to metallic transition ,with decreasing temperature.
This temperature was reduced to ⬃60 K in the sample withz⫽0.4. Finally, the z⫽0.6 sample showed neither an insulator to metal transition nor a paramagnetic to ferromagnetictransition. The temperature variation of the resistivity of thex⫽1 sample showed a negative curvature over the whole

FIG. 1. 共a兲 ab-plane normalized resistivity ␳ ab and 共b兲 ab-planemagnetization M ab for (La1⫺z Prz ) 1.2Sr1.8Mn2 O7 (z⫽0, 0.2, 0.4,
and 0.6兲 single crystals. The arrows denote the PI to FM transition
temperature. The ␳ data of the polycrystalline sample Sr3 Mn2 O7 arealso shown in the inset of 共a兲.

measured range and the value of ␳ rapidly increased by morethan four orders of magnitude, up to 2⫻106 ⍀ cm at 20 K
from ⬃100⍀ cm at room temperature 共RT兲, which is in
sharp contrast with the typical value of ⬃0.1⍀ cm at RT for
Pr-substituted samples.12,13 Recently, a theoretical bandcalculation18 predicted that the bilayer perovskite Sr3 Mn2 O7
is an antiferromagnetic insulator with an indirect gap of 0.45
eV, which is qualitatively in good agreement with our magnetization and resistivity data. Moreover, the electronic structure of this compound is expected to be similar to that of the
cubic perovskite end member CaMnO3 .
The ab-plane and the c-axis thermal conductivity of(La1⫺z Prz ) 1.2Sr1.8Mn2 O7 (z⫽0, 0.2 ,0.4, and 0.6兲 single

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ANISOTROPIC PHONON CONDUCTION AND LATTICE . . .

FIG. 2. 共a兲 ab-plane and 共b兲 c-axis thermal conductivity of(La1⫺z Prz ) 1.2Sr1.8Mn2 O7 (z⫽0, 0.2, 0.4, and 0.6兲 single crystals.
The arrows denote the PI to FM transition temperature. For comparison, the temperature variation of polycrystalline Sr3 Mn2 O7 (x⫽1) is also presented in 共a兲.

crystals are shown in Fig. 2 as a function of temperature, up
to 300 K. The arrows denote the PI to FM transition temperature. For comparison, the temperature variation of theend member polycrystalline sample Sr3 Mn2 O7 (x⫽1) isalso presented in Fig. 2共a兲. We note, first that a low thermal
conductivity was observed over a wide range of temperatures
for all samples ,in spite of the high quality of our single
crystals. Second, the temperature dependence of ␬ in the abplane exhibited anomalies associated with the PI to FM transition, while no such anomalies were observed for ␬ along
the c-axis direction near T C for any of the samples. Above
T C , the value of ␬ ab showed a positive curvature but tended
towards a constant value near room temperatures with increasing temperatures. The electron thermal conductivity forthe z⫽0 sample is estimated to be atmost ⬃1% of the total
value, even in the metallic state from the resistivity data
based on the Wiedemann-Franz 共WF兲 law and reproduce neither the whole anomaly in ␬ ab nor the giant thermal effectaround T C . 10 Thus, heat carriers are taken as phonons for all
measured samples. Here, the phonon mean free path l ph in
the insulating state of the x⫽0.4 sample is estimated fromthe specific-heat data C ph , and longitudinal sound velocity
v ph using the kinetic expression for the phonon gas ␬⫽1/3C ph v ph l ph . If C ph (150 K)⫽1.78 J/cm3 K 共Ref. 19兲
and ␬ ab (150 K)⫽11.3 mW/cm 共present data兲 for the(La1⫺z Prz ) 1.2Sr1.8Mn2 O7 single crystal (z⫽0.4) and v ph
⫽4.3⫻105 cm/s 共Ref. 20兲 in the ab plane for theLa1.2Sr1.8Mn2 O7 bilayer single crystal, we then obtainl ph,ab ⫽4.43 Å at 150 K, which is comparable with the MnO-Mn bond length (⬃4 Å). In a smilar way, the value ofl ph,ab reaches 4.07 Åat 300 K. In our estimation, the value ofv ab is taken as a constant since the relative variation of thelongitudinal velocity is very small from ultrasonic measurements on the bilayer manganites.
Next, the end member compound Sr3 Mn2 O7 showed adifferent behavior from the ab-plane data in the compound(La1⫺z Prz ) 1.2Sr1.8Mn2 O7 . The value of ␬ of the x⫽1 sample
remained almost a constant down to ⬃200 K, then showed aslight increase upon crossing T N ⫽⬃160 K and finallydropped rapidly with decreasing temperature. The temperature dependence of ␬ of the x⫽1 sample reminds us of atypical phonon conduction in insulating materials, except forthe magnitude of measured values. The extremely high resistivity of the x⫽1 (n⫽2) sample (⬃100⍀ cm at RT兲 insharp contrast with the value of ␳ ab (⬃0.1⍀ cm at RT兲 forthe Pr-substituted x⫽0.4(n⫽2) samples gives rise to a negligible contribution of small polarons, which probably results
in a typical phonon conduction. In comparison with the thermal data of the polycrystalline sample of Sr3 Mn2 O7 , lowthermal values of single-crystal samples are anomalous indicating a strong phonon damping, which correlates with dynamical lattice distortions coupled to thermally hopping of
localized carriers at Mn sites 共as discussed later兲.
We discuss the relationship between local lattice distortions and thermal conductivity in bilayer manganites. Figures
3共a兲 and 3共b兲 show the anisotropic lattice striction and volume striction for the z⫽0, 0.2, and 0.4 samples, respectively. The anomaly in anisotropic lattice striction reverses
sign near z⫽0.2 but the volume of all samples rapidly
shrinks upon crossing T C . These findings have been discussed in Ref. 21 on the basis of different relaxation models
of local lattice distortions in metal and insulating states proposed by Medarde et al.15 The authors tried to explain the
different behaviors of average and local lattice distortions
observed in neutron powder-diffraction experiments on
La2⫺2x Sr1⫹2x Mn2 O7 (0.32⭐x⭐0.4). Based on their expla-

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M. MATSUKAWA et al.

FIG. 3. 共a兲 Anisotropic lattice striction and 共b兲volume striction,
as a function of temperature, up to 300 K, for(La1⫺z Prz ) 1.2Sr1.8Mn2 O7 (z⫽0, 0.2, 0.4, and 0.6兲 single crystals.
The arrows denote the PI to FM transition temperature.

nation, the observed volume shrinkage near T C seems toarise from a strong suppression in the local lattice disordermanifested by Mn3⫹ -O6 and Mn4⫹ -O6 octahedra with the JT
distorted and undistorted sites when the system is going towards the metallic state from the insulating state. The Mn-O
bond-length distribution becomes narrower below T C because of a screening effect due to itinerant carriers. Accordingly, the phonon conduction is limited by the local latticedisorder accompanying a polaron hopping in the insulatingstate. However, in the metallic region, it is expected that thehomogenous structure of the local lattice associated with carrier delocalization causes an upturn in the ab-plane thermal
conductivity below T C . It should be noted that this conclusion is reached from the lattice striction and thermal data of
the same samples, combined with the preceding model. Furthermore, in comparison with the anisotropic Debye-Waller
共DW兲 factor of Sr3 Mn2 O7 , the anisotropic DW data of
La2⫺2x Sr1⫹2x Mn2 O7 (0.32⭐x⭐0.4) show that even in themetallic state of the latter, the inhomogeneities in the local
lattice structure still remain. This finding is probably related
not only with a small upturn in ␬ , but also to the low valuesof ␬ . On the other hand, the out-of-plane phonon conduction
across the MnO double layers is strongly disturbed fromstacking faultlike scattering of the layered structures. Phonon

FIG. 4. Normalized magnetothermal conductivity 共NMTC兲关 ␬ ab (H)/ ␬ ab (0) 兴 of (La1⫺z Prz ) 1.2Sr1.8Mn2 O7 (z⫽0, 0.2, 0.4, and0.6兲 single crystals. 共a兲z⫽0.2, 共b兲 z⫽0.4, and 共c兲 z⫽0.6. The field
was applied in the ab plane, parallel to the direction of the heatcurrent.

scattering due to stacking faults dominates thermal conduction along the c axis, masks some contribution of the local
lattice distortion associated with the insulator to metal transition and results in to the anisotropy of the thermal conductivity.
We discuss next the normalized magnetothermal conductivity 共NMTC兲 关 ␬ ab (H)/ ␬ ab (0) 兴 of the Pr-substituted crys-104433-4

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ANISOTROPIC PHONON CONDUCTION AND LATTICE . . .

FIG. 5. Normalized magnetothermal resistivity 关 ␬ ab (M )/ ␬ ab (0) 兴 ⫺1 of (La1⫺z Prz ) 1.2Sr1.8Mn2 O7 (z⫽0, 0.2, 0.4, and 0.6兲 single crystals
as a function of magnetization, at selected temperature. 共a兲z⫽0, 共b兲 z⫽0.2, and 共c兲 z⫽0.4 and 0.6. The insets in 共a–c兲represent M ab -H
curves at the corresponding temperatures for the samples with z⫽0, 0.2, and 0.6, respectively. 共d兲z dependence of coefficient A and lattice
parameter c/atals at z⫽0.2, z⫽0.4, and z⫽0.6 共Fig. 4兲. The field was in
the ab plane and parallel to the direction of the heat current.
Our data reveal several interesting features. First, a giant
magnetothermal conductivity was observed in association
with the occurrence of the CMR effect and the NMTC
reached about 30%, up to 8 T, for all samples in spite of alower T C . Here, it should be noted that ␬ c (H)/ ␬ c (0) is almost negligible in contrast with a rapid enhancement of␬ ab (H)/ ␬ ab (0), which is consistent with the absence of
anomalies observed in ␬ c (T). 10 Second, accompanying thefield-induced first-order PI to FM transition of the insulating
sample, z⫽0.6, a clear hysteresis in the magnetothermal
conductivity was observed. The remnant NMTC at 4.2 K
reached nearly the same value of ⬃10%, both in first andsecond scans, where after the first scan, the sample was
warmed up to high temperatures in order to demagnetize it.
The value of NMTC of the z⫽0.6 sample exhibited a steplike behavior at 4.2 K, while it showed a smooth rise withincreasing temperature. As previously pointed out, electronic
contribution from the WF law estimation using the CMR
data reproduces neither an upturn in ␬ ab nor a giant thermal
effect. Magnetostriction data around T C showed a volume
shrinkage upon application of a magnetic field, up to 8 T, as
well as a spontaneous striction (⬃0.1%) upon crossing
T C . 21,22 The negative magnetovolume effect indicates a suppression in local lattice disorder; the reduction in phonon
scattering due to structural disorder leads to a giant magne-

tothermal effect in the same way as the upturn in ␬
below T C .
The normalized magnetothermal resistivity 关 ␬ ab (M )/␬ ab (0) 兴 ⫺1 of our samples is plotted as a function of magnetization at selected temperatures in Figs. 5共a–c兲, where theinsets in Figs. 5共a–c兲 represent M ab -H curves at the corresponding temperatures for the samples with z⫽0, 0.2, and0.6, respectively. It is easily found that the value of the magnetothermal resistivity is scaled with a parabolic function of
1⫺A(M /M s ), 2 as pointed out for cubic manganites, by
Cohn et al.6 Here, M s is taken as the value of 3.6␮ B per Mnsites. The coefficient A depends on the value of z and showsa monotonical decrease from 0.4 for z⫽0 down to 0.28 forz⫽0.6, as shown in Fig. 5共d兲. This finding suggests a suppression of the lattice-spin coupling in thermal CMR due toPr substitution and can be explained as follows. The Pr substitution had a strong effect on the magnetic anisotropies.
The low-temperature magnetic anisotropy M ab /M c in a fieldof 100 mT reduced from ⬃10 at z⫽0 to nearly 1 at z⫽0.2
and 0.4. For z⫽0.6, the easy axis of magnetization wasalong the c axis. On the other hand, the lattice parameters
vary with Pr substitution in such a manner that the c axis
expands but the a(b) axis shrinks 关see Fig. 5共d兲兴, which
results in a change of e g -electron character from planar
3d x 2 ⫺y 2 to linear 3d 3z 2 ⫺r 2 . Accordingly, such a variation of
the e g -electron character accompanies that of magnetic anisotropy, so that Pr substitution probably suppresses indi-

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M. MATSUKAWA et al.

rectly the lattice-spin coupling in thermal CMR through avariation of spin alignment, strongly coupled with orbital
states. In other words, a higher magnetothermal conduction
favors the occurrence of the easy axis of magnetization lying
in the ab plane. It is an interesting feature that a change ofe g -electron character due to Pr substitution appears in giant
magnetothermal effect involving heat carrying phonons.
Finally, we shall stress that at lower temperatures, farfrom T C , a finite increase of ␬ ab (⬃14% at 8 T兲 for the z⫽0.2 crystal was observed. If we accept the above explanation, this finding indicates that phonon scattering due to local
lattice disorder 共bond-length fluctuation兲 remains, even in themetallic state, which is consistent with the anisotropic DW
data of La2⫺2x Sr1⫹2x Mn2 O7 (0.32⭐x⭐0.4) in the metallic
state. Recently, Maezono and Nagaosa23 pointed out that inmanganite systems, the dynamic JT effect is more enhancedin the metallic region than in the insulating region because ofstrong electron correlations. Magnetothermal measurements
at low temperatures probe the lattice disorder not only in theinsulating region but also in the metallic region as the DW
factor does. Furthermore, it is desirable to clarify the crucialrole played by the dynamic local lattice distortion on phonon
conduction not only in the insulating phase, but also in themetallic phase through magnetothermal measurements on
high-quality single crystal of the highly doped bilayer compounds.
In summary, a systematic study of thermal conductivity as
a function of temperature and magnetic field of single crystals of the compound (La1⫺z Prz ) 1.2Sr1.8Mn2 O7 for z(Pr)⫽0.2, 0.4, and 0.6 was performed. The ab-plane phonon
conduction of the Pr-substituted x⫽0.4 samples is disturbed
by the dynamical lattice distortions associated with polaron
hopping on Mn sites. On the other hand, the typical phonon
behavior observed for the end member x⫽1 sample is probably attributed to a reduction of the inhomogeneities in thelocal lattice distortions strongly coupled with small polarons.
The giant magnetothermal effect has been explained taking
into account a systematic variation of the e g -electron orbital
states due to Pr substitution.

1

11

Colossal Magnetoresistance, Charge Ordering and Related Properties of Manganese Oxides, 共edited by C.N.R. Rao and B.
Raveau 共World Scientific, Singapore, 1988兲; Colossal Magnetoresistive Oxides, edited by Y. Tokura 共Gordon and Breach,
New York, 2000兲.
2
C. Zener, Phys. Rev. 82, 403 共1951兲; P.G. de Gennes, ibid. 118,
141 共1960兲.
3
A.J. Millis, P.B. Littlewood, and B.I. Shraiman, Phys. Rev. Lett.
74, 5144 共1995兲; A.J. Millis, B.I. Shraiman, and R. Mueller,
ibid. 77, 175 共1996兲.
4
For a recent review, see E. Dagotto, T. Hotta, and A. Moreo, Phys.
Rep. 344, 1 共2001兲.
5
D.W. Visser, A.P. Ramirez, and M.A. Subramanian, Phys. Rev.
Lett. 78, 3947 共1997兲.
6
J.L. Cohn, J.J. Neumeier, C.P. Popoviciu, K.J. McClellan, and Th.
Leventouri, Phys. Rev. B 56, R8495 共1997兲.
7
S. Uhlenbruck, B. Buchner, R. Gross, A. Freimuth, A. Maria deLeon Guevara, and A. Revcolevschi, Phys. Rev. B 57, R5571
共1998兲.
8
J. Hejtmanek, Z. Jirak, M. Marysko, S. Krupicka, C. Martin, A.
Maignan, M. Hervieu, and B. Raveau, Phys. Rev. B 60, 14 057
共1999兲.
9
Y. Moritomo, A. Asamitsu, H. Kuwahara, and Y. Tokura, Nature
共London兲 380, 141 共1996兲.
10
M. Matsukawa, H. Ogasawara, R. Sato, M. Yoshizawa, R. Suryanarayanan, G. Dhalenne, A. Revcolevschi, and K. Itoh, Phys.
Rev. B 62, 5327 共2000兲.

ACKNOWLEDGMENTS

The authors would like to thank Dr. H. Ogasawara for his
technical support. This work was supported by a Grant-inAid for Scientific Research from the Ministry of Education,
Science, and Culture, Japan.

J.S. Zhou and J.B. Goodenough, Phys. Rev. B 64, 024421 共2001兲.
H. Ogasawara, M. Matsukawa, S. Hatakeyama, M. Yoshizawa,
M. Apostu, R. Suryanarayanan, G. Dhalenne, A. Revcolevschi,
K. Itoh, and N. Kobayashi, J. Phys. Soc. Jpn. 69, 1274 共2000兲.
13
M. Apostu, R. Suryanarayanan, A. Revcolevschi, H. Ogasawara,
M. Matsukawa, M. Yoshizawa, and N. Kobayashi, Phys. Rev. B
64, 012407 共2001兲.
14
Y. Moritomo, Y. Maruyama, T. Akimoto, and A. Nakamura, Phys.
Rev. B 56, R7057 共1997兲.
15
M. Medarde, J.F. Mitchell, J.E. Millburn, S. Short, and J.D. Jorgensen Phys. Rev. Lett. 83, 1223 共1999兲.
16
N. Mizutani, A. Kitazawa, O. Nobuyuki, and M. Kato, J. Chem.
Soc. 共Japan兲 Ind. Ed. 73, 1097 共1970兲.
17J.F. Mitchell, J.E. Millburn, M. Medarde, D.N. Argyriou, and J.D.
Jorgensen, J. Appl. Phys. 85, 4352 共1999兲.
18
H. Meskine, Z.S. Popovic, and S. Satpathy, Phys. Rev. B 65,
094402 共2002兲.
19
A. Vasilev, T. Voloshok, M. Apostu, R. Suryanarayanan, A. Revcolevschi, JETP Lett. 73, 630 共2001兲.
20
C.N. Brosseau, M. Poirier, R. Suryanarayanan, G. Dhalenne, and
A. Revcolevschi, cond-mat/0012380 共unpublished兲.
21
M. Matsukawa, H. Ogasawara, T. Sasaki, M. Yoshizawa, M.
Apostu, R. Suryanarayanan, A. Revcolevschi, K. Itoh, and N.
Kobayashi, J. Phys. Soc. Jpn. 71, 1475 共2002兲.
22
T. Kimura, Y. Tomioka, A. Asamitsu, and Y. Tokura, Phys. Rev.
Lett. 81, 5920 共1998兲.
23
R. Maezono and N. Nagaosa, Phys. Rev. B 67, 064413 共2003兲.
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