Inverse Magnetocaloric Effect in TbNiGe2
Sachin Gupta,* Lakhan Bainsla and K. G. Suresh
*
Department of Physics, Indian Institute of Technology Bombay, Mumbai-400076, India
Corresponding author’s e-mail: sachingupta@iitb.ac.in, Tel.: +91-9930115209; Fax: +91-22-25723480
Abstract
The TbNiGe2 compound crystallizes in CeNiSi2 type
orthorhombic crystal structure and shows antiferromagnetic
ordering below 39 K. Magnetization isotherms shows linear
dependence with field, which confirms antiferromagnetic
ordering in the compound. The compound shows inverse
magnetocaloric effect, which is attributed to antiferromagnetic
interactions between the magnetic moments in this compound.
Keywords: antiferromagnet, magnetocaloric effect.
Introduction
The rare earth intermetallic compounds with a
general formula RTX2 (R=rare earth, T=transition metal
and X=Si, Ge) and crystal structure CeNiSi2 type have
attracted considerable attention of researcher because of
its interesting magnetic and electrical properties. It has
been observed that the compounds of RTGe2 series
show different magnetic properties in a wide
temperature range [1]. Neutron diffraction carried out
for TbNiGe2 shows collinear antiferromagnetic
magnetic structure in this compound [2]. It has also
been observed that only rare earth atom in this series has
magnetic moment. There is no magnetic moment on Ni
atom. In this paper, we study structural, magnetic,
thermal and magnetocaloric properties of TbNiGe2
compound.
in the susceptibility data shows that compound
undergoes an antiferromagnetic ordering below 39 K.
the magnetization isotherms were collected in the field
up to 90 kOe. All the magnetization isotherms show
linear dependence with field, which confirms
antiferromagnetic nature of the compound. The
magnetocaloric effect (MCE) manifests as isothermal
magnetic entropy change (ΔSM) is estimated from
magnetization data using Maxwell’s relation
 M 
.
S M   
 dH

T


0
H
H
The compound shows inverse MCE (positive ΔSM)
around its ordering temperature. The negative MCE in
confirms strong antiferromagnetic ordering in this
compound. The full discussion of these results will be
given in paper later.
Experimental Details
The polycrystalline sample was prepared by arc
melting technique of the constituent elements with
purity at least 99.9 % in a water cooled copper hearth.
The formed ingot was flipped up and melted several
times for better homogeneity. Then the sample was
sealed in evacuated quartz tube and annealed for 7 days
at 800 C followed by furnace cooling. The X-ray
diffraction (XRD) pattern was obtained from X’Pert Pro
diffractometer. Magnetization M(T,H) and heat capacity
measurements were performed on physical property
measurement system (PPMS-6500).
Results and discussion
The Rietveld refinement of XRD pattern at room
temperature shows CeNiSi2 type orthorhombic crystal
structure with space group Cmcm. No detectable
impurity was seen in XRD pattern, which suggests
single-phase nature of compound.
The susceptibility data obtained in temperature range
1.8-300 K in zero field cooled (ZFC) and field cooled
(FC) mode in 500 Oe field is shown in Fig. 1. The cusp
Fig.1.Temperature
dependence
of
magnetic
susceptibility (left-hand scale) and inverse susceptibility
along with Curie-Weiss fit (right-hand scale) at 500 Oe
field.
Acknowledgment
SG thanks CSIR, Govt. of India for providing senior
research fellowship.
References
[1] A. Gill, et al., J. Magn. Magn. Mater. 129 (1994)
271.
[2] W. Bazela, et al., J. Magn. Magn. Mater 109 (1992)
305.