Magnetic properties of two new compounds: Gd2Ni3Si5 and Sm2Ni3Si5
Chandan Mazumdar, R. Nagarajan, L. C. Gupta, R. Vijayaraghavan, C. Godart et al.
Citation: J. Appl. Phys. 75, 7155 (1994); doi: 10.1063/1.356709
View online: http://dx.doi.org/10.1063/1.356709
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Published by the American Institute of Physics.
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Magnetic properties
of two new compounds:
G&Ni&i,
and Sm2Ni3Si5
Chandan Mazumdar
Indian Institute of Technology, Bombay, India 400 076
R. Nagarajan,
L. C. Gupta, and R. Vijayaraghavan
Tata Institute of Fundamental Research, Bombay, India 400 005
C. Godart
UPR-209, C.N.R.S., 92195 Meudon Cedex, France
B. D. Padalia
Indian Institute of Technology, Bombay, India 400 076
The formation of two new materials, SmzNisSi, and Gd,Ni,Si,, of the rare-earth series R,M,Si, (R
denotes rare earth and Y) and their magnetic and transport properties are reported here. These
materials crystallize in the orthorhombic U&o&-type
structure (space group Ibam). The magnetic
susceptibility of GdaNiaSis follows a Curie-Weiss behavior with an effective magnetic moment
8.1&Gd ion. The material orders antiferromagnetically at -15 K. The magnetic susceptibility of
Sm2Ni3Si5 exhibits a deviation from the Curie-Weiss behavior which is attributed to the low-lying
excited state of Sm3+ ions and also to crystal-field effects. This material also orders
antiferromagnetically, but at -11 K. This value of the ordering temperature does not seem to follow
the de Gennes scaling with respect to that of Gd,Ni&.
I. INTRODUCTION
Rare-earth (R) intermetallic materials have been of interest both in the area of fundamental physics and in application
areas. Rare-earth-based materials have interested physicists
because of the localized f-electron core and the related systematics emerging in the properties of the rare-earth series of
a system. The well-known example is the lanthanide contraction often observed in the lattice parameters of isotypic compounds of a rare-earth series. However, the electronic properties of compounds within a series do get modified in the
presence of other elements and deviations occur in the expected gradation of the properties with respect to the number
of f electrons. These deviations provide us the means to
study the physical mechanisms taking place in these materials and solids in general. For example, Ce compounds tend
to exhibit anomalous phenomenon due to hybridization of
the 4f electronic level with the 3d electronic level. This
results in the phenomenon of heavy fermion behavior, valence fluctuation (VF), Kondo effect, etc. The effects of hybridization can also modify the magnetic interactions. In
view of this, we are carrying out a program of synthesis and
study of the physical properties of new rare-earth intermetallit compounds. We initiated the study of the series of compounds R2Ni3Si5. In an earlier study, we showed the VF
behavior of Ce and Eu in Ce,Ni&
(Ref. 1) and Eu,Ni3Si,,*
respectively. The formation of Ce,Ni,Sis, Dy2Ni3Si5, and
Y2Ni3Sis has been reported in the literature.3 Here we report
the synthesis of the two new compounds, Gd,Ni,Si, and
Sm,Ni,Sis, and the preliminary results of magnetic susceptibility and resistivity studies on them.
II. EXPERIMENT
The compounds Gd,Ni,Si, and Sm,Ni,Si, were prepared
by the standard arc-melting technique using a water-cooled
copper hearth in a flowing argon atmosphere. The purity of
the starting materials was better than 99.9% for Sm, Gd, and
J. Appl. Phys. 75 (lo), 15 May 1994
Ni and better than 99.999% for Si. Each of the arc-melted
buttons was wrapped in tantalum foil, vacuum sealed in a
quartz capsule, and annealed at 1100 “C for 1 day and at
1000 “C for 7 days. The materials were characterized at
room temperature by powder-x-ray-diffraction using CuKa
radiation in a commercial x-ray diffractometer (Jeol, Japan).
Magnetic susceptibility studies were carried out using a
Faraday-type susceptometer (George Associates, U.S.A.).
The measurements were performed over the temperature
range from 4.2 to 300 K using a gas-flow-type helium cryostat. The temperature was measured by a gold-Chrome1
thermocouple.
Electrical resistivity studies over the temperature range
4.2-300 K were carried out using a home-built cryostat and
employing the standard four-probe dc method. Thin silver
wires were used as electrical leads and contacts to the
samples were made using conducting silver paint. Commercial units were used in the electrical measurements (Keithley
model 220 for current source and Keithley model 184 nanovoltmeter). In order to eliminate the effects of therm0 emf,
the resistance was first measured when the current was passing in one direction, then it was measured again with the
current passing in the reverse direction, and then the average
of these two readings was taken. The temperature was measured using a calibrated silicon diode.
Ill. RESULTS AND DISCUSSION
A. Structure
The room-temperature powder-x-ray-diffraction patterns
(Fig. 1) confirmed the formation of single-phase materials of
Gd2Ni3SiS and Sm,Ni,Sis in the orthorhombic U&o,Si,-type
crystal structure (space group Ibam) as is the case with other
known materials of this series of Ni compounds.‘-3 The unitcell parameters of the materials were determined by a leastsquares-fit procedure of the observed set of d spacing for
each material. The resulting parameters were: a=9.616 A,
0021-8979/94/75(10)/7155/3/$6.00
Q 1994 American Institute of Physics
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7155
10
20
30
40
20 in
FIG. 1. Powder-x-ray-diffraction
room temperature.
50
degree
0.004
70
60
pattern for GdzNi,Si, and Sm,Ni,Si,
at
b=11.292 A, c=5.705 8, for Sm2Ni3Si,; and a =9.560 A,
b = 11.197 A, c =5.665 A for Gd2Ni3SiS. It is pointed out that
the unit-cell parameters of Sm,Ni,Si, are smaller than those
of Gd,Ni,Si, as it should be on the basis of “lanthanide
contraction,” in which one expects the unit cell to contract as
the number of f electrons increase in a rare-earth series of
compounds.
6. Magnetic
and reslstlvlty
measurements
1. Gd&!$,
The dc magnetic susceptibility result of Gd,Ni,Si, as a
function of temperature is shown in Fig. 2. The material
appears to order magnetically, TN-15 K. From the cusplike
behavior of the susceptibility peak we infer the nature of the
ordering to be antiferromagnetic. The temperature dependence of the inverse susceptibility of %d,Ni,Si, is linear
above TN (Fig. 2). A Curie-Weiss fit to this data yielded the
magnetic moment per Gd ion to be 8.1~~. Generally, it is
believed that in materials of this structure, the transitionmetal ion does not carry the magnetic moment. In such a
case, the entire observed moment would be attributed to the
Gd ion. The moment per Gd ion in this case is slightly higher
0.5
c
15;
\
10J0
.!i
5$
0 0.4
a
g 0.3
a
L
0.2
F
= 0.1
0.0
0
0
100
Temperature
200
200
300
(K)
PIG. 3. The thermal variation of resistance (in ma) for GdzNi,Si5
than the free-ion value of Gd3’. At present we are not sure if
this slightly higher value is due to any small impurity phase
or due to intrinsic effects such as contribution from conduction electrons. We would like to point out that we synthesized and measured the magnetic susceptibility of Y,Ni,Si,
also. It was found to behave in a Curie-Weiss manner with a
magnetic moment of 0.27,qJformula unit.’ Since the Y ion is
not expected to carry any magnetic moment, if we assume
that all the moment belongs to Ni and not to any impurity
phase, then the observed moment indicates a value of
O.l6cL,/Ni ion in Y,Ni,S&.
The temperature dependence of the electrical resistance
of Gd2Ni3Si, is shown in Fig. 3. It shows a typical metallic
behavior. The reduction in the magnetic scattering of electrons below the magnetically ordered state is clearly seen.
The transition temperature seen here is consistent with that
observed through magnetic susceptibility.
2. Sm&S&.
The magnetic susceptibility of Sm2Ni3Si, is shown in
Fig. 4 as a function of temperature. An antiferromagnetic
transition is clearly seen at -11 K. It is interesting to note
that the well-known de Gennes scaling seems to be breaking
down here. The de Gennes factor for Sm with respect to Gd
is 0.28. From this one would have expected an ordering tem-
6
5.
a
-P
a
ma0
4
‘0
=3
Y
=2
300
(K)
FIG. 2. dc magnetic susceptibility and its reciprocal for the compound
GdaNi$i,. The solid line is a fit to the Curie-Weiss formula. The expanded
region near TN is shown in the inset.
7156
100
Temperature
0
100
Temperature
200
(K)
300
FIG. 4. dc magnetic susceptibility and its reciprocal for the compound
Sm,Ni&.
The expanded region near TN is shown in the inset.
J. Appl. Phys., Vol. 75, No. 10, 15 May 1994
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Mazumdar et
al.
perature of =4 K. The observed value of TN (-11 K) is
much higher than this. We believe that the small anomaly
observed in the susceptibility near 55 K is due to a small
impurity phase which is below the limit of detection in the
x-ray-diffraction pattern. The temperature dependence of inverse susceptibility is not linear. This is not unexpected in a
Sm-based material. This is primarily due to the fact that the
ionic excited states are at a rather low level and, hence, they
are also populated at moderate temperatures resulting in a
effective value of magnetic moment which is different from
that of the free Sm3’ ion in ground state. It is quite likely
that at low temperatures, crystal-field effects also contribute
to the deviation from the Curie-Weiss behavior.
IV. CONCLUSION
We have synthesized two new materials, GdaNi&
and
Sm,Ni,Si,, and shown that they form in orthorhombic
J. Appl. Phys., Vol. 75, No. 10, 15 May 1994
U,Co,Si,-type structure similar to other members of this
rare-earth series. Both the materials seems to order antiferroand
magnetically (TN=15 and ~11 K for Gd,Ni,Si,
respectively).
The
ordering
temperature
of
Sm,Ni,Si, ,
Sm,Ni,Si, does not follow the de Gennes scaling with respect to that of Gd,Ni,Si,.
ACKNOWLEDGMENT
Part of this work was supported by Project No. 509-l of
Indo-French Centre for Promotion of Advanced Research,
New Delhi, India.
‘C. Mazumdar, R. Nagarajan, S. K Dhar, L. C. Gupta, R. Wjayaraghavan,
and B. D. Padalia, Phys. Rev. B 46, 9009 (1992).
‘S. Patil, R. Nagarajan, L. C. Gupta, C. Godart, R. Vijayaraghavan, and B.
D. Padalia, Phys. Rev. B 37, 7708 (1988).
3B. Chabot and E. Parthe, J. Less-Common Met., 97, 285 (1984).
Mazumdar et al.
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7157