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Physica B 383 (2006) 22–23

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Specific heat of CuCrZrS4

M. Itoa,�, H. Yamamotob, S. Nagatab, T. Suzukia

aADSM, Hiroshima University, Higashi-Hiroshima 739-8530, JapanbDepartment of Materials Science and Engineering, Muroran Institute of Technology, Muroran, 050-8585, Japan

Abstract

We have carried out the specific heat CP measurements on thiospinel CrZrS4 which has been reported as the material shows the

ferromagnetic ordered transition at T f ¼ 60K and spin-glass freezing at T f ¼ 10K. A broad hump of CP due to spin-glass freezing is

observed around T f . We found out that there is no discontinuity as a peak or step in CP around TC.

r 2006 Elsevier B.V. All rights reserved.

PACS: 75.50.�y; 75.60.Ej; 65.40.Ba; 75.10.Nr

Keywords: Spinel compound; Spin glass; Ferromagnetic; Specific heat

1. Introduction

Thiospinel CuCr2S4 is well known that the metalliccompound which shows a ferromagnetic transition at aCurie temperature TC ¼ 377K [1–4]. The Cr ions inCuCr2S4 are in a mixed valence state with Cr3þ andCr4þ. The ferromagnetism of this compound is attributedto the double exchange interaction between Cr3þ and Cr4þ

via the conduction electrons. Padiou et al. first preparedthe CuCrZrS4 which is chemically modified compoundfrom CuCr2S4 and suggested that CuCrZrS4 also showsferromagnetic behavior [5]. High-purity specimens ofCuCrZrS4 were recently synthesized and investigated thetransport and the magnetic properties by Iijima et al. [6].They reported that the electric resistivity changes tosemiconducting and TC decreases to �60K by substitutionZr ions for half of Cr ions. In addition, a re-entrant spin-glass freezing from the ferromagnetic ordered phase isobserved at T f ’ 10K as temperature decreases.

In order to investigate the thermodynamic propertiesof CuCrZrS4, we carried out the specific heat measure-ments.

front matter r 2006 Elsevier B.V. All rights reserved.

ysb.2006.03.039

ng author. Tel.: +81824 24 7042; fax: +81 824 24 7044.

ss: showa@hiroshima-u.ac.jp (M. Ito).

2. Experimental

A polycrystalline CuCrZrS4 was prepared by a directsolid-state reaction [6]. High purity fine powders of Cu(99.99%), Cr (99.99%), Zr (99.9%) and S (99.999%) weremixed in stoichiometric ratio and were reacted in a sealedquartz tube at 750 �C for 7 days. After being pulverized, thespecimen was pressed into rectangular bars and sintered at750 �C for 2 days. Specific heat CPðTÞ were measured by arelaxation method using the commercial calorimeter(Quantum Design, PPMS).

3. Results

Fig. 1 shows temperature T dependence of specific heatCPðTÞ of CuCrZrS4 in 1:8pTp80K. Remarkably, noanomaly is observed in CPðTÞ around the Curie tempera-ture TC ’ 60K which was determined from the magnetiza-tion measurements in the previous report [6]. The reason ofno anomaly in CPðTÞ around TC is still unclear. We arenow considering the two possibilities. One is that thespin-glass like phase transition occurs at TC. The other isthat the localized spins are strongly polarized by theconduction electrons even above TC as seen in LaCrSb3 [7].In order to clarify this amazing behavior, detail study isneeded.

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80

60

40

20

0

CP (

J/K

mol

)

806040200

T C

0.4

0.3

0.2

0.1

0

CP /T

(J/

K2 m

ol)

20151050

T f

T (K)

CuCrZrS4

T (K)

Fig. 1. Temperature T dependence of specific heat CP of CuCrZrS4. An

inset is the plot of CP=T as a function of T. Curie temperature TC and

spin-glass freezing temperature T f were determined by the magnetization

measurements [6].

M. Ito et al. / Physica B 383 (2006) 22–23 23

As shown in the inset of Fig. 1, a broad hump appearsaround 10K in the CPðTÞ=T plot as a function of T. Thistemperature coincides with the re-entrant spin-glass transi-tion temperature T f obtained from the magnetizationmeasurements [6]. It is well known that specific heat ofspin-glass system, for example AuFe [8], shows the broadhump around the spin-glass freezing temperature. Ourresult suggests that the spin-glass phase exists below T f .

4. Conclusion

We have studied thermodynamic properties of thiospinelcompound CuCrZrS4 which was reported as the re-entrantspin-glass material with Curie temperature TC ’ 60K andspin-glass freezing temperature T f ’ 10K. The broadhump suggesting spin-glass freezing and no anomaly inCPðTÞ are observed at T f and TC, respectively.

Acknowledgments

This work was partially supported by a Grant-in-Aidsfor COE Research (No. 13CE2002), the Scientific Research(No. 16740205) and (No. 17340113) fromMEXT Japan, anaid fund from Energia (Hiroshima) and the Asahi GlassFoundation (Tokyo).

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