Physica B 329–333 (2003) 924–925

Thermal conductivity of Pr0:65ðCa1Z SrZ Þ0:35MnO3 underapplied ﬁeld
Yohei Kashiwada, Hiroyuki Fujishiro*, Manabu Ikebe
Faculty of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551, JapanAbstract
The thermal conductivity kðTÞ of Pr0:65 ðCa1Z SrZ Þ0:35 MnO3 (0pZp1:0) has been measured under the applied ﬁeldof up to 5 T: For Z ¼ 0:3 and 0.4, where the ferromagnetic metal (FM-M) state is competitive with the charge/orbital
ordered (CO/OO) state, kðTÞ is enhanced and shows the hysteresis below the FM-M transition temperature Tc : Thehysteresis of kðTÞ is wiped out and Tc increases rapidly with the increase of the applied ﬁelds. These kðTÞ behaviors
originate from the stabilization of the FM-M state due to the rapid suppression of the CO/OO state.
r 2003 Elsevier Science B.V. All rights reserved.
Keywords: Pr0:65 ðCa1Z SrZ Þ0:35 MnO3 ; Thermal conductivity; Ferromagnetic metal; Charge/orbital order

1. Introduction

2. Experimental

In the RE1X AEX MnO3 manganites (RE and AE
being the trivalent rare-earth elements and divalent
alkaline-earth ones, respectively), the electrical andmagnetic properties are dependent on the hole concentration X (band ﬁlling) and the effective one-electron
bandwidth W [1]. If the average radius of RE1X AEX
ions decreases, W is reduced and the charge/orbitalordered (CO/OO) state becomes dominant over the
ferromagnetic-metal (FM-M) phase. By alloying a larger
AE ion at a constant X ; Pr0:65 ðCa1Z SrZ Þ0:35 MnO3
undergoes the transition from the CO/OO insulatingphase ðZp0:1Þ to the FM-M phase ðZX0:4Þ [2]. Thephonon component of the thermal conductivity kðTÞ ofLa1X AEX MnO3 systems ðAE ¼ Ca; Sr) shows acharacteristic enhancement below the FM-M transitiontemperature Tc [3,4]. The kðTÞ enhancement is also
observed at the ﬁeld-induced FM-M transition in
Pr0:65 Ca0:35 ðMn1Z CoZ ÞO3 system [5]. In this paper, we
report kðTÞ of the Pr0:65 ðCa1Z SrZ Þ0:35 MnO3 system
under the applied ﬁelds.

Thesingle-phase
Pr0:65 ðCa1Z SrZ Þ0:35 MnO3(0pZp1:0) polycrystals were prepared by a solid-state
reaction method. kðTÞ was measured by a steady-stateheat ﬂow method using an automated measuringapparatus [6]. The electrical resistivity rðTÞ was measured by a four-probe method. The magnetization MðTÞwas measured using a SQUID magnetometer under
0:5 T in the process of zero ﬁeld cooling (ZFC).

*Corresponding author. Fax: +81-19-621-6373.
E-mail address: fujishiro@iwate-u.ac.jp (H. Fujishiro).

3. Results and discussion
Fig. 1(a) shows MðTÞ as a function of temperature T:
The CO/OO insulating phase is stable for Zp0:1 andthe FM-M phase is stable for ZX0:6 at low temperatures. In the intermediate Z region ð0:2pZp0:4Þ; theCO/OO insulating phase is competitive with the FM-Mphase. Figs. 1(b) and (c) show rðTÞ of the Z ¼ 0:3 and0.4 samples, respectively. For Z ¼ 0:3; the characteristicrðTÞ upturn is observable below the CO/OO transition
temperature TCO ¼ 210 K and the FM-M state isinduced below TcðdownÞ ¼ 70 K and TcðupÞ ¼ 100 K inzero ﬁeld. In the 2 T ﬁeld, Tc increases rapidly withapplied ﬁelds and the hysteretic rðTÞ behavior is0921-4526/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0921-4526(02)02604-2

Y. Kashiwada et al. / Physica B 329–333 (2003) 924–925

925

Fig. 2. Magnetic ﬁeld dependence of kðTÞ for the (a) Z ¼ 0:3
and (b) Z ¼ 0:4 samples.
Fig. 1. (a) MðTÞ for the Pr0:65 ðCa1Z SrZ Þ0:35 MnO3 samples
ð0:1pZp0:6Þ: The electrical resistivity rðTÞ of the (b) Z ¼ 0:3
and (c) 0.4 samples under the magnetic ﬁelds.

completely wiped out at 5 T: For Z ¼ 0:4; the hysteresisof rðTÞ can be seen at 0 T; which is completely wipedout for BX2 T: The hysteresis suggests the survival ofthe CO/OO order at 0 T:Figs. 2(a) and (b) show kðTÞ of the Z ¼ 0:3 and 0.4
samples under the applied ﬁelds. In both samples, kðTÞis overwhelmingly due to phonons. In Fig. 2(a), at 0 T
on the cooling run, kðTÞ is enhanced below TcðdownÞ ¼
70 K and then reaches a maximum at 40 K anddecreases with decreasing T: On the subsequent heatingrun, kðTÞ is drastically reduced at TcðupÞ ¼ 90 K andmonotonously increases with the further increase of T:
When the 2 T ﬁeld is applied, the hysteretic kðTÞbehavior becomes broarder and TcðdownÞ and TcðupÞ
rapidly increase to B200 K: For the applied ﬁeld of
5 T; kðTÞ does not show the hysteresis and Tc increases
to 220 K: In Fig. 2(b), the absolute values of kðTÞ arelarger than those for Z ¼ 0:3 and the hysteresis isobservable only at 0 T: These hysteretic kðTÞ behaviors
are consistent with those of rðTÞ as shown in Fig. 1. In
accord with rðTÞ and kðTÞ behaviors, the thermalexpansion dLðTÞ=L of the Z ¼ 0:3 sample (not shown)shows a clear contraction below Tc accompanying alarge hysteresis in 0 and 2 T:

With increasing mobility of the charge carriers due tothe metallic conduction, the local Jahn–Teller (JT)lattice distortion is relaxed in the FM-M phase as theobserved contraction of dL=L indicates [4]. The kðTÞenhancement below Tc is considered to originate fromthe reduced phonon scattering as a result of the relaxed
local JT distortion. The disappearance of the hysteresisin kðTÞ suggests that the CO/OO phase gives place to theFM-M phase in the applied ﬁeld and the existence of theCO/OO phase brings about the rapid increase of Tc inthe applied ﬁeld.

References[1] A. Asamitsu, Y. Moritomo, Y. Tomioka, T. Arima, Y.
Tokura, Nature 373 (1995) 407.
[2] M.R. Lees, J. Barratt, G. Balakrishnan, D. McK. Paul, C.
Ritter, Phys. Rev. B 58 (1998) 8694.
[3] M. Ikebe, H. Fujishiro, Y. Konno, J. Phys. Soc. Japan 67(1998) 1083.
[4] H. Fujishiro, M. Ikebe, in: H. Ohyanagi, A. Bianconi (Eds.),
Physics in Local Lattice Distortions, AIP, New York, 2001,
p. 433.
[5] H. Fujishiro, S. Kanoh, H. Yamazaki, M. Ikebe, J. Phys.
Soc. Japan 70 (2001) 2616.
[6] M. Ikebe, H. Fujishiro, T. Naito, K. Noto, J. Phys. Soc.
Japan 63 (1994) 3107.