Physica B 291 (2000) 225}227

Anisotropic magnetization in RTe2

(R: Ce, Pr, Gd and Sm)q

Y.S. Shin!, C.W. Han", B.H. Min!, H.J. Lee!, C.H. Choi#, Y.S. Kim#, D.L. Kim#,Y.S. Kwon!,",*

!Department of Physics and Institute of Basic Science, Sung Kyun Kwan University, 300, Cheoncheondong, Jangangu,Suwon 440-746, South Korea

"Center for Strongly Correlated Materials Research, Seoul National University, Seoul, South Korea#Korea Basic Science Institute, Taejeon 305-333, South Korea

Received 6 December 1999

Abstract

The magnetic susceptibility and the magnetization were measured for CeTe2

(d2), PrTe2, SmTe

2and GdTe

2with

HDDab-plane and HDDc-axis. All except for GdTe2

have a strong anisotropy due to their crystalline "elds in paramagneticregion. A few magnetic phase transitions in all, except for PrTe

2, are observed in low-temperature region. Especially, the

various magnetic-phase transitions are found in CeTe2

and SmTe2. ( 2000 Elsevier Science B.V. All rights reserved.

Keywords: Rare-earth ditellurides; Magnetic anisotropy; Magnetization

Rare-earth ditellurides have a strong anisotropyin various physical properties for a two-dimen-sional crystalline structure and thus have attractedgreat interest in the "eld of condensed matter phys-ics. CeTe

2among rare-earth ditellurides was the

most investigated and most of its studies have beencarried out in transport [1], speci"c heat [2] andelectron microprobe analysis [3]. Though the ex-perimentally evaluated number of carriers is verysmall, &1015/cm3, it behaves as typical heavy fer-mion materials. It has also been found to showa magnetic transition around 4.5K from previousmeasurements such as resistivity and speci"c heat.From the electron microprobe analysis, it is foundthat LaTe

2has a charge density wave (CDW).

Though many interesting phenomena have been

qPresented at SCES'99, 24}28 August 1999, Nagano, Japan.*Corresponding author. Tel.: #82-331-290-7049; fax: #82-

331-290-7055.E-mail address: yskwon@yurim.skku.ac.kr (Y.S. Kwon).

observed in these samples, they have a strongdependence on sample's stoichiometry. Therefore,we manufacture single crystals of these samples andinvestigate their magnetic structures by measuringmagnetization and magnetic susceptibility in thepresent work.

The preparation of samples was referred in Ref.[4]. Using a SQUID magnetometer established inKorea Basic Science Institute (KBSI), we have mea-sured the magnetization and magnetic susceptibil-ity. These measurements were carried out intemperature regions from 2 to 300K under appliedmagnetic "elds up to 70 kOe.

The temperature dependence of the magneticmoments in low-temperature regions and the mag-netic susceptibilities in the paramagnetic regions atan applied "eld of H"500 Oe and the magnetiz-ation curves at several temperatures are shown inFigs. 1}3 for CeTe

2(d2), PrTe

2, SmTe

2and

GdTe2, respectively. The H/M, which means 1/s, in

the paramagnetic regions of CeTe2, PrTe

2and

0921-4526/00/$ - see front matter ( 2000 Elsevier Science B.V. All rights reserved.PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 2 8 3 - 8

Fig. 1. Temperature dependence of the magnetic moments inlow-temperature regions for CeTe

2(d2), PrTe

2, SmTe

2and

GdTe2.

Fig. 2. Magnetic susceptibilities in the paramagnetic regions atan applied "eld of H"500 Oe for CeTe

2(d2), PrTe

2, SmTe

2and GdTe

2.

Fig. 3. Magnetization curves at several temperatures for CeTe2

(d2), PrTe2, SmTe

2and GdTe

2.

GdTe2

are linear to temperature. Their e!ectivemagnetic moments per rare-earth ion evaluated bythe slopes of the averaging H/M, which is de"nedas the inverse of (s

##2s

!")/3, above 150K amount

to 2.59, 4.07 and 8.18kB, respectively. It means that

each rare-earth ion has three valence. In SmTe2,

however, the H/M value gets saturated in high-temperature, which seems to be due to the vanVleck term of J"7/2. The M/H data in CeTe

2,

PrTe2

and SmTe2

show a large anisotropy andtheir c-axis are easy axes. In GdTe

2with very weak

crystal "eld, however, the anisotropy hardly ap-

pears in M/H. Therefore, the anisotropy is thoughtto be caused by the contribution of the crystal "eld.CeTe

2has three magnetic transitions at about 5.3,

4.1 and 3.5K. Two magnetic transitions in SmTe2

appear at about 4 and 3.5K. The magnetictransitions in GdTe

2occurs at about 9.8K. How-

ever, PrTe2

has no magnetic transition in the tem-perature down to 2K. The value of M/H in low-temperature region below 10K is smaller than thatof Curie}Weiss law. It means that the ground statein PrTe

2is the singlet split from J"4 multiplet

caused by the e!ect of crystal "eld. As shown inFig. 1, the magnetization M in CeTe

2at 2 K with

Hoab-plane suddenly increases at about 600 Oeand is saturated to about 1.2k

B, which seems to be

the magnetic moment of the ground doublet con-sidering the e!ect of orthorhombic crystal "eld.M increases gradually with increasing temperatureand approaches to 1.2k

Bwith increasing magnetic

"eld. On the other hand, M with HDDab-plane at alltemperatures gradually increase with increasingmagnetic "eld and reach at 60% of 1.2k

B.

This indicates that the CeTe2

is ferromagnet or

226 Y.S. Shin et al. / Physica B 291 (2000) 225}227

ferrimagnet in higher magnetic "eld than about 600Oe. An interesting point is that a small magneticmoment (0.1k

Bin Hoab-plane and 0.01k

Bin

HDDab-plane) as even H"0 is retained in lower-temperature regions than 5K. This indicates thatthe magnetic structure in low-temperature regionsis a small canted antiferromagnetic. In SmTe

2,

M simply increases with increasing magnetic "eldat all temperatures except 2K. At ¹"2 K a meta-magnetic transition is observed at H"3.5T. Incase of GdTe

2, since the magnetic moments in both

magnetic "eld directions below 9.8K decreasewith decreasing temperature and the spontaneousmagnetization is not observed, the magnetic phasebelow the temperature is thought to be antifer-romagnetic. Furthermore, the di!erence of M be-tween Hoab- and HDDab-plane below the temper-ature is small as about 10% and M in bothdirections is almost in the ratio with increasingmagnetic "eld. This suggests that the antiferromag-

netic spins are not aligned to the crystal axes andthe magnetocrystalline anisotropy is small.

Acknowledgements

This paper was supported by the Korea Scienceand Engineering Foundation through Grant Nos.96-0702-02-01-3, and 961-0210-147-2 and Centerfor Strongly Correlated Materials Research(CSCMR) at Seoul National University.

References

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Suzuki, J. Magn. Magn. Mater. 140}144 (1995) 1173.[3] E. DiMasi, B. Foran, M.C. Aronson, S. Lee, Phys. Rev. B 57

(1996) 13587.[4] Y.S. Kwon, B.H. Min, Physica B 281&282 (2000) 120.

Y.S. Shin et al. / Physica B 291 (2000) 225}227 227