ARTICLE IN PRESS

Journal of Magnetism and Magnetic Materials 272–276 (2004) 1798–1799

Lattice effect on ferromagnetic-metal phase transition in
Pr0:65Ca0:35ðMn1Z CoZ ÞO3 and Pr0:65Ca0:35ðMn1Z CrZ ÞO3
Manabu Ikebe , Hiroyuki Fujishiro*, Shingo Kanoh, Hajime Yamazaki
Faculty of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551, JapanAbstract
The lattice effects have been studied on the transition to ferromagnetic-metal state caused by Co, Cr and Ni doping in
Pr0:65 Ca0:35 MnO3 : The contrasting behavior of the thermal expansion LðTÞ=L20 and the phonon thermal conductivity
kph ðTÞ observed for Co and Cr (Ni) doping is attributable to the difference in the charge order (CO) states, i.e., longranged (Co-doping) CO or short-ranged (Cr-, Ni-doping) one. The nonmagnetic low spin state of doped Co3þ ions inthe insulating CO phase may be a possible origin to make the difference.
r 2003 Elsevier B.V. All rights reserved.
PACS: 75.30.Kz; 65.40.b; 66.60.þf
Keywords: Pr0:65 Ca0:35 MnO3 ; Co and Cr doping; Charge order; Thermal expansion; Thermal conductivity

1. Introduction
In the perovskite-type manganites RE1X AEX MnO3
(RE ¼ La; Pr, Nd etc., AE ¼ Ba; Sr, Ca), the competition of the ferromagnetic-metal (FM-M) phase and thecharge-ordered (CO) insulator phase stages intriguing
physical properties such as the colossal magnetoresistance (CMR). Because of the narrow electron bandwidth W due to the small ionic radii of Pr and Ca, theCO phase is stabilized in Pr1X CaX MnO3 over a wide
range of the carrier concentration X ð0:30oX p0:75Þ
[1,2] and the ferromagnetic insulating (FM-I) phaseappears for X p0:30: The CO state, however, is not quite
stable and the FM-M phase is realized for 0:30X p0:50
by applying the magnetic ﬁeld H or by doping asmall amount (2–4%) of other 3d-transition metalelement (M) at Mn sites. In this note, we study
the induced transition to the FM-M phase in
Pr0:65 Ca0:35 ðMn1Z MZ ÞO3 (M ¼ Co; Cr, Ni). Because
the Jahn–Teller (J–T) lattice distortions around Mn3þ
spins are considered to be an important key factor to*Corresponding author. Tel.: +81-19-621-6362; fax: +8119-621-6373.
E-mail addresses: ikebe@iwate-u.ac.jp (M. Ikebe),
fujishiro@iwate-u.ac.jp (H. Fujishiro).

determine the physical properties of the present system,
we investigate the lattice effect by measuring the thermal
expansion and the phonon thermal conduction.

2. Results and discussion
Pr0:65 Ca0:35 ðMn1Z MZ ÞO3 polycrystals were preparedfrom stoichiometric mixtures of Pr6 O11 ; CaCO3 ; Mn3 O4and CoO (CrO, NiO) powders by a standard solid-state
reaction method [3]. The electrical resistivity rðTÞ wasmeasured by a four-terminal method and the magnetization MðTÞ was measured by a SQUID magnetometer.
The thermal expansion LðTÞ=L20 (¼ the sample length
at temperature T normalized by that at 20 K) wasmeasured by a strain gauge method. The thermalconductivity kðTÞ was measured by a continuous heat
ﬂow method.
Fig. 1(a) shows MðTÞ of Pr0:65 Ca0:35 ðMn0:96 M0:04 ÞO3(PCMO(M)) under the ﬁeld of 0:5 T: The MðTÞ curves
for PCMO(Cr) and PCMO(Ni) gradually increases
below Tc like a usual ferromagnet with second-order
FM transition. In contrast, MðTÞ of PCMO(Co) almost jumps up at Tc with decreasing T; which isindicative of a typical ﬁrst-order transition. Fig. 1(b)presents rðTÞ of respective samples. All the samples

0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2003.12.1060

ARTICLE IN PRESS
M. Ikebe et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 1798–1799
4Tc

3

2

M=Co (5T)
M=Cr (0T)
M=Cr (5T)1µ0H=0.5T(a)~10-3(a)

0
M=non
M=Co
M=Cr
M=Ni106105M=non
M=Co
M=Cr20(mW/cmK)Resistivity (m Ωcm)

M=non
M=Co
M=Cr
M=Ni

M=Co (0T)

L(T)/L20

Magnetization (µB/Mn)

Pr0.65Ca0.35(Mn0.96M0.04)O3

1799

104103

1510Tc5102
TCO
1010(b)100200Temperature (K)

0300

(b)

0100
200
Temperature (K)300

Fig. 1. (a) MðTÞ and (b) rðTÞ for the Pr0:65 Ca0:35 ðMn1Z MZ ÞO3samples (M ¼ non; Co, Cr, Ni).

Fig. 2. (a) LðTÞ=L20 and (b) kðTÞ for the Pr0:65 Ca0:35
ðMn1Z MZ ÞO3 samples (M ¼ non; Co, Cr).

exhibit metal–insulator (M–I) transition, taking a rðTÞmaximum in the vicinity of Tc : The rðTÞ curves ofPCMO(Cr) and PCMO(Ni) are very much alike and theM–I transitions are rather gradual. It is to be noticed,
however, that rðTÞ exhibits a clear hysteresis between
cooling and heating scans. In contrast, PCMO(Co)shows a very sharp M–I transition, which is also
accompanied by a hysteresis.
Fig. 2(a) shows LðTÞ=L20 of PCMO(Co) andPCMO(Cr), where we notice much contrasting behaviours. With decreasing T; LðTÞ=L20 of PCMO(Co)exhibits a sharp shrink at Tc ; while the corresponding
shrink is absent for PCMO(Cr). The shrink is alsoabsent for PCMO(Ni). The sharp shrink of LðTÞ=L20
was observed for La1X CaX MnO3 at the ﬁrst order-like
M–I transition and was attributed to the release of theJ–T lattice distortions in the metallic phase [4]. Fig. 2(b)displays kðTÞ vs. T: The heat conduction in the present
specimens is overwhelmingly due to phonons because ofthe large rðTÞ: With decreasing T; kðTÞ of PCMO(Co) isenhanced step-like at Tc ; while very gradual k enhancement is barely noticeable for PCMO(Cr). The kenhancement in the FM-M phase has been explained
as to originate from the reduction of phonon scattering
by local J–T distortions [5].
Now, we brieﬂy discuss the origin of the difference in
the FM-M transitions. In the present PCMO system, theFM-M phase is realized at an expense of the CO statedamage caused by the 3d-element doping. By theelectron microscope measurement, Katsufuji et al. [6]observed the change of the long-ranged CO to the shortranged one as a result of Cr doping. The short-rangedCO is consistent with our observation for PCMO(Cr)and PCMO(Ni) but the present results for PCMO(Co)suggest that the long-ranged CO may survive after Codoping. It is widely accepted that the ground state ofCo3þ ions in insulating LaCoO3 is nonmagnetic lowspin state. The Co3þ low-spin state should be morestable in the PCMO system because of the stronger
crystalline ﬁeld due to the smaller lattice parameter. The
origin of the survival of long-ranged CO may beascribed to nonmagnetic Co3þ because the local(magnetic) interaction with neighbouring Mn spinsshould be then by far weaker. In the FM-M phase ofLa1X SrX CoO3 ; the intermediate Co spin state is known
to be stabilized. It is very intriguing to elucidate the Co
spin state in the FM-M phase of PCMO(Co). The larger
saturation moment of PCMO(Co) than PCMO(Cr) andPCMO(Ni) in Fig. 1(a) may imply the magnetic Co ionsin the FM-M phase. The microscopic study forPCMO(Co) is necessary.
This work was partially supported by a Grant-in-Aidfor Scientiﬁc Research from the Ministry of theEducation, Culture, Sports, Science and Technology,Japan (No. 14550661).

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[2] Y. Tomioka, et al., Phys. Rev. B 53 (1996) R1689.
[3] M. Ikebe, et al., J. Phys. Soc. Jpn. (Suppl.) 71 (2002)
145.
[4] M. Ikebe, et al., Physica B 316–317 (2002) 265.
[5] H. Fujishiro, et al., J. Phys. Soc. Jpn. 70 (2001) 2616.
[6] T. Katsufuji, et al., J. Phys. Soc. Jpn. 68 (1999) 1090.