Crystal structure and ferromagnetic ordering of REPt3 (RE = Gd, Tb) compounds
Sudipta Mondal , Chandan Mazumdar*, R. Ranganathan
ECMP Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata - 700064
E-mail: *chandan.mazumdar@saha.ac.in
Abstract: Two compounds, GdPt3 and TbPt3 have been synthesized and characterized by the powder X-ray
diffraction at room temperature. The compounds form essentially in the C15b structure. The dc magnetization
measurements show that GdPt3 and TbPt3 order ferromagnetically at about T C ~36 K and 16 K respectively.
1. INTRODUCTION
The Rare Earth (RE) and Transition metal (M)
based binary compounds of the general formula REM3
exhibits various interesting physical properties such as
superconductivity [1], magnetocaloric effects [2] etc.
One of such series is REM3 compounds. These
compounds actually form in different crystal
structures for different transition metals. For instance,
the REPd3 series crystallize in the AuCu3 structure [3]
with the Pm-3m space group symmetry, whereas the
REPt3 compounds with light RE metals (La-Tb) have
the disordered C15b type Laves phase structure (space
group F-43m) [4]. The TbPt3 can also be obtained in
the AuCu3 type structure after annealing at 1173 K for
2 hrs. Although the preliminary magnetic properties of
some members of the REPt3 series have been reported
earlier [5], the detail magnetic properties of this series
are yet to be investigated. In this work, we report the
magnetic properties of GdPt3 and TbPt3, beyond
which the series ceased to form in C15b type
structure.
respectively. These values are close to the theoretical
free ion values 7.94 µB/f.u and 9.72 µB/f.u of Gd3+ and
Tb3+ ions. The paramagnetic Curie temperatures (θp)
are 40.6 K and 17 K for GdPt3 and TbPt3 respectively
which are very close to their TC. The positive values
of θp indicate presence of ferromagnetic type of
interactions in these compounds. The field dependent
magnetization behaviour reveal that the magnetization
value at 2 K reaches about 7.16 µB/f.u for GdPt3 and
5.87 µB/f.u for TbPt3 in 9T field. For GdPt3 this value
matches with the theoretical saturated state magnetic
moment (7 µB) of Gd3+ ion. However, 5.87 µB/f.u is
much smaller compared with the theoretical value (9
µB/f.u) of Tb3+ ion. This reduction may be due to the
presence of crystal field effects and magnetic
anisotropy. In the field dependence magnetization,
GdPt3 does not show any hysteresis, even at 2K.
However, in the TbPt3 compound there exists a
hysteresis loop at low field regions at 2K which is also
consistent with the divergence between the ZFC and
FC magnetization. The existence of ferromagnetism is
also confirmed by the Arrott plot.
2. EXPERIMENTAL DETAILS
The polycrystalline samples of GdPt3 and TbPt3 are
synthesized by arc melting and characterized by the
powder X-ray diffraction (XRD) technique at room
temperature. The zero-field cooled (ZFC) and field
cooled (FC) dc magnetization was measured in the
temperature range 2-300 K at various applied
magnetic fields.
3. RESULTS AND DISCUSSIONS
The powder XRD patterns at room temperature
reveal that the compounds essentially form in single
phase having the C15b type crystal structure. The
cubic lattice parameters of GdPt3 and TbPt3 are
7.561Å and 7.541Å respectively, in good agreement
with the previously reported data.
The GdPt3 and TbPt3 appear to order
ferromagnetically at about T C ~36K and ~16K
respectively [Fig.1]. In case of TbPt3, the ZFC and FC
magnetization do not follow the same path below T C.
The divergence between ZFC and FC magnetization
could be attributed to the magnetic anisotropy in this
compound. On the other hand GdPt3 does not show
any such divergence as Gd has no magnetic
anisotropy (angular momentum, L= 0). The CurieWeiss fit of the inverse paramagnetic susceptibility
yield the effective magnetic moment (µeff) value of
GdPt3 and TbPt3 to be 8.16 µB/f.u and 9.75 µB/f.u
Fig.1. ZFC and FC magnetization at 1000 Oe applied
field of GdPt3 and TbPt3 compounds.
4. CONCLUSIONS
The two compounds, GdPt3 and TbPt3, form in the
C15b type structure and order ferromagnetically at
about 36 K and 16 K respectively.
REFERENCES
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