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Spin-glass behaviour in CdFe1−xSbx system
Solid State Communications, Vol. 74, No. 11, pp. 1213-1216, 1990. Printed in Great Britain.
0038-1098/90 $3.00 + .00 Pergamon Press plc
SPIN-GLASS BEHAVIOUR IN CdFe~ xSb~ SYSTEM H. Mohan and R.G. Kulkarni Department of Physics, Saurashtra University, Rajkot 360 005, India
(Received 21 January 1990 by S. Amelinckx) The magnetic properties of the semimagnetic semiconductor CdFe~ _xSbx (x = 0, 0.2, 0.4, 0.6, 0.8) have been investigated experimentally using a.c.-susceptibility (xa.c), magnetization and M6ssbauer spectroscopic techniques. All samples exhibit sharp cusps at the freezing temperatures (Ts) in x,c - Tdata resembling those of spin-glasses. The observation of M6ssbauer spectra consisting of a quadrupole doulet superimposed on Zeeman split pattern and finite magnetic moments for x = 0 and 0.2 suggest that these materials behave like "cluster spin-glass", while for x = 0.4, 0.6 and 0.8, absence of Mossbauer spectra and zero magnetic moments indicate that the spin-glass type of freezing is due to Van Vleck type paramagnetic ion clusters.
1. INTRODUCTION SPIN-GLASS transitions in magnetic conductors and magnetic insulators have received much attention in recent years mainly because of their great potential in the research on the microscopic mechanisms involved in the spin-glass behaviour [1]. Bond frustration [2], i.e. the impossibility of satisfying all the magnetic interactions simultaneously, is the main cause for spin-glass behaviour. A prerequisite for the spinglass type of frozen spins to occur is the presence of random competition between ferromagnetic and anti-ferro magnetic interactions. CUMn [3], AUFe [4], Cd~_xMnxTe [5], Hej_xMnxTe [6], etc. are called typical spin-glass systems which are prepared by introducing magnetic 3d-transition metal impurities into nonmagnetic matrices. Extensive studies have been done on spin-glass (SG) in the last decade. One of the most interesting problems in this field has been whether an equilibrium phase transition does exist in SG or not. Various kinds of SG materials have been reported that are characterized with a.c. susceptibility (appearance of a cusp at the freezing temperature, TI) and/or magnetization (presence of remanence below TI) measurements. The intermetallic compound CdFe is a binary alloy system, whose behaviour is very similar to the typical spin-glass systems. This is because of the fact that an exactly equiatomic CdFe alloy (1 : l) is a ferromagnet. Antimony (Sb) is a nonmagnetic. The substitution of Sb for Fe in CdFe denoted as CdGe~_xSbx leads to two distinct kinds of SG materials for x = 0.2, 0.4. 0.6, 0.8 and x = 0.1, 0.3, 0.5, 0.7, 0.9, respect-
ively. The increase of Fe dilution, x, in CdFe~ xSbx reduces ferromagnetic interactions and enhanced antiferromagnetic interactions. In this paper we present results of the low field a.c.-susceptibility upto 700 K, magnetization and M6ssbauer measurements on the CdFet_xSbx system for x = 0, 0.2, 0.4, 0.6 and 0.8. The system under investigation CdFeT_xSbx is known as semimagnetic semiconductor (SMSC) II-V containing Fe 2+ ions for which no measurements have been reported so far. 2. EXPERIMENTAL The CdFej_xSb x alloys were prepared by appropriately mixing the stoichiometric amounts of high purity (99.9%) constituent elements. The mixed powders were sealed under high vacuum in a quartz ampoule. Five samples with x = 0.0, 0.2, 0.4, 0.6, and 0.8 were synthesized by induction melting. Powder X-ray diffraction patterns were recorded on a philips diffractometer using FeK~ radiation to characterize the samples. The a.c.-susceptibility measurements on powdered samples were made in the temperature range 77 K to 700 K using the double coil set up [7] operating at a frequency of 263 Hz and in r.m.s, field of 0.5 Oe. Magnetization measurements at room temperature and 77 K were carried out using the high field hysteresis loops technique [8]. The M6ssbauer spectra were obtained with a constant acceleration transducer and a 256 multi-channel analyser operating in time mode. A gamma source 57Co (pd) of a specific activity of 10 mCi was used. All spectra were obtained at room temperature (300 K) in transmission geometry.
1213
1214
SPIN-GLASS B E H A V I O U R IN CdFe~ xSbx SYSTEM
Vol. 74, No. 11
3. R E S U L T S A N D DISCUSSION X:O.O
From X-ray diffraction studies, all five samples (x = 0.0, 0.2, 0.4, 0.6, and 0.8) were found to be single phase metallic alloys. Figure 1 shows the temperature dependencies of a.c.-susceptibility (x,c) for CdFe~ ,Sb,~ alloys with x = 0.0, 0.2, 0.4, 0.6 and 0.8. All the x,c data presented here (Fig. 1) have been obtained on zero field cooled (ZFC) samples i.e. the samples were cooled to 77 K in zero applied field, the field desired is then turned on and held constant and Xac is recorded by slowly heating the sample to 700K. Measurements were also made by cooling the sample to 77 K in the presence of an externally applied low a.c. field. However, no appreciable difference was observed in the x,~. vs temperature curves obtained by heating and cooling the sample. This is consistent with the notion that x .... is a measure of the reversible part of the susceptibility. It is evident from Fig. 1 that the Xac. (T) data show sharp cusp like peaks at temperatures (Tt) defined as freezing temperatures and reproducible to within 0.5 K. The observed peaks in Xa.c.(T) data (Fig. 1) have a striking resemblance to those of spin-glass type of freezing. The :harpness and amplitude of the cusp and decrease with increasing "x". Tf varies linearly with x (Fig. 2). The Curie temperatures (TN) and the freezing temperatures (To) obtained from Fig. 1 for all samples are listed in Table 1. The saturation magnetization and the magneton number nB (the saturation magnetization per formula unit in Bohr magneton) at 300 K obtained from hysteresis loop technique for all samples are summarized in Table 1. From field dependence of magnetization and observed magnetic moments (Table 1), it is clear that the samples with x = 0.0 and 0.2 show ferromagnetic behaviour, while the samples with x = 0.4, 0.6 and 0.8 exhibit Van Vleck type paramagnetism (vanishingly small magnetic moments) or antiferromagnetism. All samples show no coercive field (He) at 77K. At 300K, Hc is absent for x = 0.0 and 0.2 samples and it is present for x = 0.4, 0.6 and
Table 1. Magnetic data for CdFel_xSbx system x
0.0 0.2 0.4 0.6 0.8
A.c.-susceptibility
Magnetization
TI (K)
TN (K)
a, (emu/g)
nB (#B)
453 461 451 442 433
535 563 543 503 503
91.6 4.7 0.0 0.0 0.0
2.74 0.16 0.00 0.00 0.00
+ 1 __+ 1 __ 1 ___+1 _____1
+ 1 _____1 ___+ 1 __ 1 _____1
2.7 2.3
1.9
1.5
1.1
O2 1.2
1.0
O.B
O.S 1.3
X=0.4
< N 0.9
0.5
0.1
0.9
--
0.7
--
05 . ~ 10 . 06 . 02 . ;-
~e
1.4
100
X O :8 .
I 200
300
z.O0
500
600
700
Temperature (T) K
Fig. 1. The temperature dependencies o f a.c.-susceptibility for CdFel_xSbx (x = 0.0, 0.2, 0.4, 0.6 and 0.8) system.
Vol. 74, No. I !
S P I N - G L A S S B E H A V I O U R IN CdFe~ ,Sb,. SYSTEM
1215
6/-. 62
/,6O X=~O
60
58
~-~~ 0 tn
½
~2o
X
0.2
O.t.
0.6
0.8
1.0
8/X
Fig. 2. Variation of freezing temperature (Ts) with Fe dilution (x).
82
_
~
)(=02 .
80
0.8 samples which increases to higher values for increasing temperatures. These H,. observations suggest that samples with x = 0.4, 0.6 and 0.8 are not anti-ferromagnetic. Figure 3 shows M6ssbauer spectra at 300 K for x = 0.0 and 0.2 At x = 0, the spectrum exhibits well defined six lines (magnetic) pattern with zero isomer and quadrupole shifts. For x = 0.2, the spectrum consists of a paramagnetic doublet superimposed on six line pattern. In order to fit such spectrum, it is necessary to allow the paramagnetic subspectrum (Hhf = 0) to have a quadrupole splitting different from the quadrupole shift (Q.S.) of the magnetic parts (Hhf > 0, Q.S. is zero in this case). As no M6ssbauer spectra were observed for x = 0.4, 0.6 and 0.8 at 300 K much below Ts, it is evident that these samples are not antiferromagnetic. From a.c.-susceptibility, magnetization, and M6ssbauer data, it is apparent that on increasing dilution of Fe or x, the collinear ferromagnetic phase breaks down before reaching the ferromagnetic percolation limit as a result of the presence of competing exchange interactions. In this dilution region (x = 0.0 and 0.2) there is a second transition, at Ti, to a spinglass-like (SGL) state, well below the ferromagnetic ordering temperature Tu. The observed maxima in Xa.c. -- T curve (Fig. 1) for x = 0.0 and 0.2 may be attributed to the single domain to superparamagnetic (SD-SP) transition and the decrease in xa.c at lower temperatures suggest that these materials behave like "cluster spin-glass" [9]. This is the usual behaviour met in systems having superparamagnetic ferromagnetic clusters with no long-range ferromagnetic order, which is further confirmed by observation of paramagnetic doublet in the hyperfine distribution of M6ssbauer spectrum for x = 0.2 (Fig. 3) at T < Tr.
78
0
30
60 90 120 Chonne[Number
Fig. 3. M6ssbauer spectra of CdFe~ xSb,. system for x = 0.0 and 0.2 at 300K.
One would also observe similar M6ssbauer spectrum f o r x = 0 a t T w i t h Tf > T > 300K. Absence of magnetization (magnetic moments) and quadrupole doublet in M6ssbauer spectra for x = 0.4, 0.6 and 0.8 samples, it is suggestive that these samples are neither anti-ferromagnetic nor ferromagnetic. Therefore, it is totally ruled out that the peaks observed in x .... - T curve (Fig. 1) for these samples are not due to the N6el type of a material ordering anti-ferromagnetically. Much interest has recently been attracted by SMSC's containing Fe 2+ ions incorporated in I I - I V semiconductor matrices [10] such as Znl_xFexSe, Znl xFexTe, or Cd~_xFexSe. The Fe 2+ ion possesses in these alloys a non-magnetic ground state and exhibits Van Vleck paramagnetism. This fact is related to the presence of a non-vanishing orbital momentum in the 3d 6 configuration of the Fe 2+ ion (L -- 2, S -- 2). In particular, we believe that the CdFe~_xSbx system for x = 0.4, 0.6 and 0.8 contains Fe 2+ ions in non-magnetic ground state and exhibits Van Vleck type paramagnetism as demonstrated by magnetization and M6ssbauer measurements (zero magnetic moments and absence of M6ssbauer spectrum) at 300 K. Further the spin-glass type of freezing observed in x .... - T curves (Fig. 1) as peaks for x = 0.4, 0.6 and 0.8 are due to Van Vleck type paramagnetic ion clusters or spin clusters, an exact physical mechanism for this phenomenon is rather difficult to comprehend at present.
1216
SPIN-GLASS BEHAVIOUR IN CdFe~_xSbx SYSTEM
The use of M6ssbauer spectroscopy, as we have reported here, has the advantage of measuring a local property, while the susceptibility and magnetization are of course global measurements for studying ferromagnetic spin-glass mixed system. Further work is necessary to elucidate the nature of the Van Vleck type of paramagnetic ion cluster spin-glass. Acknowledgements - The authors are thankful to Drs R.V. Upadhyay, H.H. Joshi, S.N. Rao, H.N. Pandya and G.J. Baldha for fruitful discussions. One of the authors (H.M.) is grateful to the University Grants Commission, New Delhi, for providing financial support in the form of a Fellowship.
2. 3. 4. 5. 6. 7. 8. 9. 10.
REFERENCES 1.
C.Y. Huang, J. Magn. Magn. Mater. 51, 1 (1985).
Vol. 74, No. I I
G. Toulouse, Commun. Phys. 2, 115 (1977). O.S. Lutes & J.L. Schmit, Phys. Rev. 125, 433 (1962). R.A. Brand, J. Lauer & D.M. Herlach, J. Phys. F: Met Phys. 13, 675 (1983). M. Escorne, A. Mauger, R. Triboulet & J.L. Tholence, Physica 107B, 309 (1981). S. Nagata, R.R. Galazka, D.P. Mullin, H. Akbarzadh, G.D. Khattak, J.K. Furdyna & P.H. Keesom, Phys. Rev. B22, 3331 (1980). C. Radhakrishnamurty, S.D. Likhite & P.W. Sahasrabudhe, Proc. Indian Acad. Sci. 87A, 245 (1978). C. Radhakrishnamurty, S.D. Likhite & N.P. Sastry, Philos. Mag. 23, 503 (1971). A.P. Murani, J. Phys. F4, 757 (1974). A. Mycielski, J. Appl. Phys. 63, 3279 (1988).
0038-1098/90 $3.00 + .00 Pergamon Press plc
SPIN-GLASS BEHAVIOUR IN CdFe~ xSb~ SYSTEM H. Mohan and R.G. Kulkarni Department of Physics, Saurashtra University, Rajkot 360 005, India
(Received 21 January 1990 by S. Amelinckx) The magnetic properties of the semimagnetic semiconductor CdFe~ _xSbx (x = 0, 0.2, 0.4, 0.6, 0.8) have been investigated experimentally using a.c.-susceptibility (xa.c), magnetization and M6ssbauer spectroscopic techniques. All samples exhibit sharp cusps at the freezing temperatures (Ts) in x,c - Tdata resembling those of spin-glasses. The observation of M6ssbauer spectra consisting of a quadrupole doulet superimposed on Zeeman split pattern and finite magnetic moments for x = 0 and 0.2 suggest that these materials behave like "cluster spin-glass", while for x = 0.4, 0.6 and 0.8, absence of Mossbauer spectra and zero magnetic moments indicate that the spin-glass type of freezing is due to Van Vleck type paramagnetic ion clusters.
1. INTRODUCTION SPIN-GLASS transitions in magnetic conductors and magnetic insulators have received much attention in recent years mainly because of their great potential in the research on the microscopic mechanisms involved in the spin-glass behaviour [1]. Bond frustration [2], i.e. the impossibility of satisfying all the magnetic interactions simultaneously, is the main cause for spin-glass behaviour. A prerequisite for the spinglass type of frozen spins to occur is the presence of random competition between ferromagnetic and anti-ferro magnetic interactions. CUMn [3], AUFe [4], Cd~_xMnxTe [5], Hej_xMnxTe [6], etc. are called typical spin-glass systems which are prepared by introducing magnetic 3d-transition metal impurities into nonmagnetic matrices. Extensive studies have been done on spin-glass (SG) in the last decade. One of the most interesting problems in this field has been whether an equilibrium phase transition does exist in SG or not. Various kinds of SG materials have been reported that are characterized with a.c. susceptibility (appearance of a cusp at the freezing temperature, TI) and/or magnetization (presence of remanence below TI) measurements. The intermetallic compound CdFe is a binary alloy system, whose behaviour is very similar to the typical spin-glass systems. This is because of the fact that an exactly equiatomic CdFe alloy (1 : l) is a ferromagnet. Antimony (Sb) is a nonmagnetic. The substitution of Sb for Fe in CdFe denoted as CdGe~_xSbx leads to two distinct kinds of SG materials for x = 0.2, 0.4. 0.6, 0.8 and x = 0.1, 0.3, 0.5, 0.7, 0.9, respect-
ively. The increase of Fe dilution, x, in CdFe~ xSbx reduces ferromagnetic interactions and enhanced antiferromagnetic interactions. In this paper we present results of the low field a.c.-susceptibility upto 700 K, magnetization and M6ssbauer measurements on the CdFet_xSbx system for x = 0, 0.2, 0.4, 0.6 and 0.8. The system under investigation CdFeT_xSbx is known as semimagnetic semiconductor (SMSC) II-V containing Fe 2+ ions for which no measurements have been reported so far. 2. EXPERIMENTAL The CdFej_xSb x alloys were prepared by appropriately mixing the stoichiometric amounts of high purity (99.9%) constituent elements. The mixed powders were sealed under high vacuum in a quartz ampoule. Five samples with x = 0.0, 0.2, 0.4, 0.6, and 0.8 were synthesized by induction melting. Powder X-ray diffraction patterns were recorded on a philips diffractometer using FeK~ radiation to characterize the samples. The a.c.-susceptibility measurements on powdered samples were made in the temperature range 77 K to 700 K using the double coil set up [7] operating at a frequency of 263 Hz and in r.m.s, field of 0.5 Oe. Magnetization measurements at room temperature and 77 K were carried out using the high field hysteresis loops technique [8]. The M6ssbauer spectra were obtained with a constant acceleration transducer and a 256 multi-channel analyser operating in time mode. A gamma source 57Co (pd) of a specific activity of 10 mCi was used. All spectra were obtained at room temperature (300 K) in transmission geometry.
1213
1214
SPIN-GLASS B E H A V I O U R IN CdFe~ xSbx SYSTEM
Vol. 74, No. 11
3. R E S U L T S A N D DISCUSSION X:O.O
From X-ray diffraction studies, all five samples (x = 0.0, 0.2, 0.4, 0.6, and 0.8) were found to be single phase metallic alloys. Figure 1 shows the temperature dependencies of a.c.-susceptibility (x,c) for CdFe~ ,Sb,~ alloys with x = 0.0, 0.2, 0.4, 0.6 and 0.8. All the x,c data presented here (Fig. 1) have been obtained on zero field cooled (ZFC) samples i.e. the samples were cooled to 77 K in zero applied field, the field desired is then turned on and held constant and Xac is recorded by slowly heating the sample to 700K. Measurements were also made by cooling the sample to 77 K in the presence of an externally applied low a.c. field. However, no appreciable difference was observed in the x,~. vs temperature curves obtained by heating and cooling the sample. This is consistent with the notion that x .... is a measure of the reversible part of the susceptibility. It is evident from Fig. 1 that the Xac. (T) data show sharp cusp like peaks at temperatures (Tt) defined as freezing temperatures and reproducible to within 0.5 K. The observed peaks in Xa.c.(T) data (Fig. 1) have a striking resemblance to those of spin-glass type of freezing. The :harpness and amplitude of the cusp and decrease with increasing "x". Tf varies linearly with x (Fig. 2). The Curie temperatures (TN) and the freezing temperatures (To) obtained from Fig. 1 for all samples are listed in Table 1. The saturation magnetization and the magneton number nB (the saturation magnetization per formula unit in Bohr magneton) at 300 K obtained from hysteresis loop technique for all samples are summarized in Table 1. From field dependence of magnetization and observed magnetic moments (Table 1), it is clear that the samples with x = 0.0 and 0.2 show ferromagnetic behaviour, while the samples with x = 0.4, 0.6 and 0.8 exhibit Van Vleck type paramagnetism (vanishingly small magnetic moments) or antiferromagnetism. All samples show no coercive field (He) at 77K. At 300K, Hc is absent for x = 0.0 and 0.2 samples and it is present for x = 0.4, 0.6 and
Table 1. Magnetic data for CdFel_xSbx system x
0.0 0.2 0.4 0.6 0.8
A.c.-susceptibility
Magnetization
TI (K)
TN (K)
a, (emu/g)
nB (#B)
453 461 451 442 433
535 563 543 503 503
91.6 4.7 0.0 0.0 0.0
2.74 0.16 0.00 0.00 0.00
+ 1 __+ 1 __ 1 ___+1 _____1
+ 1 _____1 ___+ 1 __ 1 _____1
2.7 2.3
1.9
1.5
1.1
O2 1.2
1.0
O.B
O.S 1.3
X=0.4
< N 0.9
0.5
0.1
0.9
--
0.7
--
05 . ~ 10 . 06 . 02 . ;-
~e
1.4
100
X O :8 .
I 200
300
z.O0
500
600
700
Temperature (T) K
Fig. 1. The temperature dependencies o f a.c.-susceptibility for CdFel_xSbx (x = 0.0, 0.2, 0.4, 0.6 and 0.8) system.
Vol. 74, No. I !
S P I N - G L A S S B E H A V I O U R IN CdFe~ ,Sb,. SYSTEM
1215
6/-. 62
/,6O X=~O
60
58
~-~~ 0 tn
½
~2o
X
0.2
O.t.
0.6
0.8
1.0
8/X
Fig. 2. Variation of freezing temperature (Ts) with Fe dilution (x).
82
_
~
)(=02 .
80
0.8 samples which increases to higher values for increasing temperatures. These H,. observations suggest that samples with x = 0.4, 0.6 and 0.8 are not anti-ferromagnetic. Figure 3 shows M6ssbauer spectra at 300 K for x = 0.0 and 0.2 At x = 0, the spectrum exhibits well defined six lines (magnetic) pattern with zero isomer and quadrupole shifts. For x = 0.2, the spectrum consists of a paramagnetic doublet superimposed on six line pattern. In order to fit such spectrum, it is necessary to allow the paramagnetic subspectrum (Hhf = 0) to have a quadrupole splitting different from the quadrupole shift (Q.S.) of the magnetic parts (Hhf > 0, Q.S. is zero in this case). As no M6ssbauer spectra were observed for x = 0.4, 0.6 and 0.8 at 300 K much below Ts, it is evident that these samples are not antiferromagnetic. From a.c.-susceptibility, magnetization, and M6ssbauer data, it is apparent that on increasing dilution of Fe or x, the collinear ferromagnetic phase breaks down before reaching the ferromagnetic percolation limit as a result of the presence of competing exchange interactions. In this dilution region (x = 0.0 and 0.2) there is a second transition, at Ti, to a spinglass-like (SGL) state, well below the ferromagnetic ordering temperature Tu. The observed maxima in Xa.c. -- T curve (Fig. 1) for x = 0.0 and 0.2 may be attributed to the single domain to superparamagnetic (SD-SP) transition and the decrease in xa.c at lower temperatures suggest that these materials behave like "cluster spin-glass" [9]. This is the usual behaviour met in systems having superparamagnetic ferromagnetic clusters with no long-range ferromagnetic order, which is further confirmed by observation of paramagnetic doublet in the hyperfine distribution of M6ssbauer spectrum for x = 0.2 (Fig. 3) at T < Tr.
78
0
30
60 90 120 Chonne[Number
Fig. 3. M6ssbauer spectra of CdFe~ xSb,. system for x = 0.0 and 0.2 at 300K.
One would also observe similar M6ssbauer spectrum f o r x = 0 a t T w i t h Tf > T > 300K. Absence of magnetization (magnetic moments) and quadrupole doublet in M6ssbauer spectra for x = 0.4, 0.6 and 0.8 samples, it is suggestive that these samples are neither anti-ferromagnetic nor ferromagnetic. Therefore, it is totally ruled out that the peaks observed in x .... - T curve (Fig. 1) for these samples are not due to the N6el type of a material ordering anti-ferromagnetically. Much interest has recently been attracted by SMSC's containing Fe 2+ ions incorporated in I I - I V semiconductor matrices [10] such as Znl_xFexSe, Znl xFexTe, or Cd~_xFexSe. The Fe 2+ ion possesses in these alloys a non-magnetic ground state and exhibits Van Vleck paramagnetism. This fact is related to the presence of a non-vanishing orbital momentum in the 3d 6 configuration of the Fe 2+ ion (L -- 2, S -- 2). In particular, we believe that the CdFe~_xSbx system for x = 0.4, 0.6 and 0.8 contains Fe 2+ ions in non-magnetic ground state and exhibits Van Vleck type paramagnetism as demonstrated by magnetization and M6ssbauer measurements (zero magnetic moments and absence of M6ssbauer spectrum) at 300 K. Further the spin-glass type of freezing observed in x .... - T curves (Fig. 1) as peaks for x = 0.4, 0.6 and 0.8 are due to Van Vleck type paramagnetic ion clusters or spin clusters, an exact physical mechanism for this phenomenon is rather difficult to comprehend at present.
1216
SPIN-GLASS BEHAVIOUR IN CdFe~_xSbx SYSTEM
The use of M6ssbauer spectroscopy, as we have reported here, has the advantage of measuring a local property, while the susceptibility and magnetization are of course global measurements for studying ferromagnetic spin-glass mixed system. Further work is necessary to elucidate the nature of the Van Vleck type of paramagnetic ion cluster spin-glass. Acknowledgements - The authors are thankful to Drs R.V. Upadhyay, H.H. Joshi, S.N. Rao, H.N. Pandya and G.J. Baldha for fruitful discussions. One of the authors (H.M.) is grateful to the University Grants Commission, New Delhi, for providing financial support in the form of a Fellowship.
2. 3. 4. 5. 6. 7. 8. 9. 10.
REFERENCES 1.
C.Y. Huang, J. Magn. Magn. Mater. 51, 1 (1985).
Vol. 74, No. I I
G. Toulouse, Commun. Phys. 2, 115 (1977). O.S. Lutes & J.L. Schmit, Phys. Rev. 125, 433 (1962). R.A. Brand, J. Lauer & D.M. Herlach, J. Phys. F: Met Phys. 13, 675 (1983). M. Escorne, A. Mauger, R. Triboulet & J.L. Tholence, Physica 107B, 309 (1981). S. Nagata, R.R. Galazka, D.P. Mullin, H. Akbarzadh, G.D. Khattak, J.K. Furdyna & P.H. Keesom, Phys. Rev. B22, 3331 (1980). C. Radhakrishnamurty, S.D. Likhite & P.W. Sahasrabudhe, Proc. Indian Acad. Sci. 87A, 245 (1978). C. Radhakrishnamurty, S.D. Likhite & N.P. Sastry, Philos. Mag. 23, 503 (1971). A.P. Murani, J. Phys. F4, 757 (1974). A. Mycielski, J. Appl. Phys. 63, 3279 (1988).