ARTICLE IN PRESS

Physica B 378–380 (2006) 499–500
www.elsevier.com/locate/physb

Thermal conductivity anomaly in La0.52Ca0.48MnO3 under applied ﬁeld
Hiroyuki Fujishiro, Manabu Ikebe
Faculty of Engineering, Iwate University, Morioka, 020-8551, Japan

Abstract
The temperature and magnetic ﬁeld dependences of the thermal conductivity k(T, B) have been investigated for La0.52Ca0.48MnO3.
k(T, B) markedly changes at the phase transition between the charge-orderd antiferromagnetic (CO-AFM) state and the ferromagnetic(FM) metal state. k(T, B) is enhanced in the FM state because the phonon scattering by the local Jahn–Teller strain around Mn3+ spinsis released in the metallic phase. The k(T, B) behaviors can be understood on the basis of the volume fraction ratio of the FM and COAFM phases.
r 2006 Elsevier B.V. All rights reserved.
PACS: 65.40.b; 66.30.Xj; 75.47.Lx
Keywords: Thermal conductivity; Manganites; Charge order; Ferromagnetic order; Phonon scattering

1. Introduction
In the perovskite manganite La1-XCaXMnO3 system,
where the lattice, charge and spin are closely andcomplicatedly correlated with each other, a variety ofdramatic phenomena such as the colossal magnetoresistance (CMR) and the insulator–metal (IM) transition takeplace. The thermal conductivity k(T) measurement can be auseful tool to investigate the effect of the lattice dynamics
on the phase transitions. For 0.19pXp0.45, k(T) increases
abruptly at the onset of metallic phase below theferromagnetic (FM) transition temperature Tc mainly due
to the reduction of the local lattice distortion. For X0.50,
where the Mn3+ and Mn4+ ions exist in nearly equal
number, the charge-ordered antiferromagnetic (CO-AFM)
state competitive to the FM state appears. The k(T)reduction is observable around the CO transition temperature TCO, which originates from the locking of the local
strain as a result of reduced charge carrier hopping [1]. The
coexistence of the CO-AFM phase and the FM orparamagnetic phase for X ¼ 0:47 and 0.49 in our sample
was conﬁrmed by the X-ray diffraction under applied ﬁelds

Corresponding author. Tel.: +81 19 621 6363; fax: +81 19 621 6363

E-mail address: fujishiro@iwate-u.ac.jp (H. Fujishiro).
0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2006.01.216

and the volume fraction VFM of the FM-phase wasestimated [2].
In this paper, we investigate the temperature andmagnetic ﬁeld dependences of the thermal conductivityk(T, B) for La0.52Ca0.48MnO3 sample and discuss the k(T, B) anomalies around these phase boundaries.
2. Results and discussion
The La0.52Ca0.48MnO3 polycrystal was fabricated by astandard solid-state reaction method [1]. The thermalconductivity k(T, B) was measured by a steady-state heat
ﬂow method from 10 to 300 K applying a magnetic ﬁeld up
to 5 T parallel to the heat ﬂow direction in the processes ofzero ﬁeld cooling (ZFC), ﬁeld cooling (FC) and ﬁeldwarming (FW). The measurement error in k due to theradiation loss is within 10% at 300 K The magnetization
M(T, B) was measured using a SQUID magnetometer.
Fig. 1(a) shows k(T) in various magnetic ﬁelds and Fig.
1(b) shows k(T) in B ¼ 5 T in the ZFC, FC and FW runs.
Fig. 1(c) presents M(T, B). The FM and the CO-AFM
transition temperatures were determined as T c ¼ 230 K
and T CO ¼ 160 K in B ¼ 0:05 T, respectively. Because ofthe high electrical resistivity, the heat conduction is almost
due to phonons (k ¼ kph). k(T,0) in zero ﬁeld monotonically decreases with decreasing T and then shows a plateau

ARTICLE IN PRESS
H. Fujishiro, M. Ikebe / Physica B 378–380 (2006) 499–500

500

40
X=0.46 (0T)

3M (µB /Mn)

(a)

20

X=0.50 (0T)10

La0.52Ca0.48MnO3210K

1100K(b)0(b)
 (mW/cmK)

200T
1T-FC
3T-FC
3T-FW
5T-FC

TCO(0T)

T (5T)c

200T
5T-ZFC
5T-FC
5T-FW
100T (K)

200

4300

0.05T-FC
1T-FC
3T-FC
3T-FW
5T-FC
5T-FW
5T-FC

(c)
3FC-5T2

1FW-5T
ZFC-5Tx100030

201030100

M (µB /Mn)

170K

Tc(0T)

 (mW/cmK)

 (mW/cmK)30(a)100200300

T (K)Fig. 1. (a) k(T) for the La0.52Ca0.48MnO3 sample in the magnetic ﬁelds. (b)k(T) in B ¼ 5 T in ZFC, FC and FW runs. (c) M(T) in the magnetic ﬁelds.

below 200 K. For B ¼ 1 and 3 T in the FC run, k(T) isenhanced below Tc and shows a local maximum. Below
TCO, k(T) is suddenly reduced and then approaches thek(T,0) curve. k(T) shows a large hysteresis around TCO
similar to M(T) shown in Fig. 1(c), which suggests that aﬁrst-order phase transition between FM and CO-AFM
state takes place. k(T) in B ¼ 5 T is enhanced at low
temperatures compared with that for B ¼ 3 T, but issmaller than that for the X ¼ 0:46 sample. The FM stateis fully present in the X ¼ 0:46 specimen and the CO-AFMstate is fully present in the X ¼ 0:50 specimen. The FM
volume fraction VFM at low T estimated from the210K
170K100K
0

1

23Field (T)45Fig. 2. The magnetic ﬁeld dependences of (a) M(B) and (b) k(B) for theLa0.52Ca0.48MnO3 at T ¼ 210, 170 and 100 K.

measured M value increases with increasing applied ﬁeldand reaches about 35% in B ¼ 5 T.
The magnitude of k changes depending on the VFMvalue. It should be noted that the k(T) in the CO-AFM
phase is smaller than that in the FM phase. These results
suggest that the phonon scattering is enhanced in the COAFM phase due to the increase of local lattice distortion
below TCO as observed by the thermal dilatation [3].
In Fig. 1(b), k(T), in B ¼ 5 T shows a relatively small
hysteresis around TCO for the FC and FW runs in contrast
to M(T). In the 5 T-ZFC run, k(T) remains at the low value
below T CO ¼ 130 K but suddenly jumps to the high value
just above TCO.
Fig. 2 shows the magnetic ﬁeld dependence of (a) M(B)and (b) k(B) at T ¼ 210, 170 and 100 K. M(B) and k(B)increase with increasing applied ﬁeld at T ¼ 210 and
170 K. On the other hand, at T ¼ 100 K, these quantities
show no ﬁeld dependence up to 5 T which suggests thestable CO-AFM phase.
In summary, the thermal conductivity k(T, B) of theLa0.52Ca0.48MnO3 sample changes depending on the charge
and magnetic order. The phonon thermal conductivity kph
is enhanced in the FM-metal phase, while it is reduced in
the CO-AFM phase. The novel k(T, B) behaviors can beunderstood on the basis of the volume fraction VFM of theFM phase in accord with the previous results of the X-raydiffraction.
References[1] H. Fujishiro, M. Ikebe, in: H. Oyanagi, A. Bianconi (Eds.), Physics in
Local Lattice Distortions, American Institute Physics, 2001, p. 443.
[2] Y. Watanabe, K. Takahashi, S. Awaji, K. Watanabe, H. Fujishiro,
M. Ikebe, J. Phys. Soc. Japan 72 (2003) 817.
[3] H. Fujishiro, T. Fukase, M. Ikebe, J. Phys. Soc. Japan 70 (2001) 628.