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Structural and magnetic properties of some mixed Li-Cd ferrites
FAaterials
ELSEVIER
Chrmibtry
and Physics 52 ( 1998)
166-169
Structural and magnetic properties of some mixed Li-Cd ferrites S.S. Bellad *, R.B. Pujar, B.K. Chougule h4oterials
S&me
Lnbomtorv,
Deparinwnt
of Pi+-isius,
Shivirji
University,
K01Imp:w
416004,
Indin
Received 3 June 1997: received in revised form 15 July 1997; accepted 20 August 1997
Abstract Polycrystalline L&Cd ferrites with the general formula Li,,,-,,, Cd,, Fe2,5--.r,204 are preparedby the standard ceramic technique. The Xray analysis reveals single phase formation of ferrite samples. The lattice parameter increases linearly with Cd’+ content, which can be attributed to ionic volume differences of the component cations involved. The bondlengths R, and R, increases as Cd content increases. The increase in bondlength R, with Cd content suggests that the iono-covalent character of the spine1 decreases. The magnetic moment (np) increases with Cd content up to s = 0.3, and then decreases with a further increase in X. The increase in magnetization can be explained on the basis of Neel’s two sublattice model whereas decrease in magnetization is attributed to the presence of a triangular arrangement of spins on 0 1998 Elsevier Science %A. the B-site and hence can be explained on the three sublattice model as suggested by Yafet and Kittel. Kqsrx~ds:
Magnetic
propcrtics;
Lithium
k&es;
Structural
properties
1. Introduction Lithium ferrites have become very altractive for microwave applications especially as a replacement for garnets owing to their low cost. Squareness of the hysteresis loop along with superior temperature performance due to a high Curie temperatureare other prominent properties that have tnade them very promising candidates for microwave devices. Several studieshave beenreportedwith the addition of divalent, trivalent and tetravalent ions in lithium ferrite [ l&4]. In fact, cadmium is substitutedto study a wide range of saturation magnetization values. Ravinder and Seshagiri Rao [S] studied the electrical and thermoelectric power of Li-Cd ferrites andfound n-type conduction. RadhaandRavinder [ 61 also studiedthe Li-Cd ferrites for their frequency andcompositionaldependenceof dielectric behaviour. However, no reports have beenfound in the literature regarding structural and magnetic properties in general and lattice parameter, bond lengths, saturation magnetization, Y-K anglesin particular in the mixed L&Cd ferrites sintered at 1000°C.Therefore in this communication,we report on compositional variation of lattice parameter.bond lengths,Bohr magneton,Curie temperatureetc. of Li-Cd ferrites. 2. Experimental The Li-Cd ferrite having the general formula Li0.5-s,2Fe,,,-,,zCd,rO, (where .u=O, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and * Corresponding
author.
OX&0584/98/$19.00 PII s0253-0584(97)02022-
0
1998 Ekvier 1
Science
S.A. All rights
reserved
0.7) were preparedby standardceramic technique usingAR grade oxides as starting materials.The oxides were mixed in stoichiometric proportions and the mixture was presintered at 750°C for 10 h. The resultant powder was used to make pellets (diameter= 1 cm, thickness= 0.3 cm) for magnetic hysteresisloop measurements,which were finally sinteredat 1000°Cfor 24 h and slowly cooledto room temperature.The final sintering temperaturewas fixed to 1000°Cby considering the volatility of lithium above this temperatureand to get fine particles. The completion of the solid state reaction wasconfirmed by X-ray diffraction studiescarried out on the powder sampleswith a PHILIPS PW-1710 diffractometer usingCuKol radiation (A = 1.5418A). All the samplesshow singlephaseformation.
3. Resultsand discussion Fig. 1 showsthe variation of lattice parametern with the content of cadmium in the presentL& -,,2Fe,,S -.~&d.~Ol ferrite system.It can be seenthat, with increasingthe content of cadmium, the lattice parameterincreasesmonotonically. The linear variation of lattice parameterwith the content of cadmium
shows that the system obeys the Vegard’s
law. This
be explained on the basisof the ionic volume differences between the comp?nent ions. Sinct the ionic radii of Cd’+ andLi ’ + are0.99 A [ 121and 0.70 A [ 131,respectively, and the content of Cd’+ increaseswhile that of Li’ + along with can
L67
8.*08
00 01
Fig. I. Variation
I 0.0
02
Ob
05
06
Cd CONTENT (X) of lattice parameter tz with content of cadmium
/ 0.1
I 0.2 Cd
Fig. 2. Variation
03
of bondlrngtha
I 0.3
I 04
CONTENT (X) -, (R,, R,) with content
the Fe3 + ions decrease, it is expected that the lattice parameter should increase with the cadmium substitution. Fig. 2 shows the compositional variation of bondlengths R, and R, with cadmium content. The bond lengths R, and R, were calculated using the relations
I 0.5
(s),
I 0.6
of cadmium
I
(1).
R,=aJ3(6+1/8)
(1)
R,=a(36’-6/2+1/16)“’
(2)
and 6= U-O.375 is the deviation from the u-parameter. The value of L[= 0.380 for pure lithium ferrite was taken. R, is
168 Table I Compositional Sr. No.
1 2 3
4 5 6 7
S.S. Beilod
variations
of different
et nl. /Muterials
Chemistq
52 (I 998) 166-169
parameters
Composition
Lattice parameter
Y-K
x
a ch 8.282
Lie J-h Lb J-b LL Lb, Lb
and Physics
sFez.s04 4sFe2.45Cdo ,04 J~~~~CCIO dh &%.&do 3% 3oFez.30C4 4, 25Fe2.&d0.50J d~dXd&
8.325 8.379 8.384
angles
4TrMs
Curie temperature
%I.
(G)
Perm.
0 0 0 0
3514
2.59
4214 4135 5176
3.20 3.65 3.79
350
502 402 327
4437
3.32
250
252
3548
2.79
152
2112
1.63
155 82
8.351
18"31'
8.487 8.523
35%
’
W36'
the shortest distance between A-site cation and oxygen ion and Rn is the shortest distance between B-site cation and oxygen ion. It is dear from Fig. 2 that both R, and RB increase linearly with content ofcadmium in the samples. The increase of average bondlength R, with Cd content can be associated with the increase in the lattice parameter. Since n increases with Cd content (Fig. 1)) the increase in R, with Cd content is anticipated. Levine [7], in his work on bond susceptibility in spinels, has shown that there exists an inverse relationship between the covalent character of spine1 and bond length. From Fig. 2 it is seen that as the content of Cd in the ferrite increases, the bond length RB also increases, indicating the decrease of iono-covalent character with increase of Cd content. Similar results have been reported by Sawant and Suryavanshi [ 81 in the case of the Cu-Zn ferrite system. From the high field hysteresis loop studies, the magneton numbers, i.e. the saturation magnetization per formula unit in Bohr magnetons, were calculated using the relation
I$=
Mol. WeightXSaturation 5585
690 52.5 395
Magnetization
np=(6Sx)cos
a,,-5(1-X)
Cd
Fig. 3. Variation
of Bohr magneton
80
(3)
(41
1 0.2
675
The variation of magnetic moment (no) with the content of cadmium is shown in Fig. 3. The trend observed is very much similar to the variation of np with composition in CuZn [9], Mg-Zn [ lo], Li-ZrZn [ 111 and Cd-Cu [ 121 ferrite systems. The value of Bohr magneton ( na) for Li-ferrite in our system is in good agreement with the earlier reported value 1:131. Whatever deviation exists may be due to porosity, defects introduced at the time of sintering, different condi-
1% 0 0.1
A.c. susc.
The experimentally determined values of Bohr magneton, Curie temperatures measured from initial permeability and a.c. susceptibility studies are given in Table 1, along with the calculated values of Yafet-Kittel (Y-K) angles using the relation
T 4.0 0-
0.0
(“C)
0.3 CONTENT(X)
04
C-5
0.6
_____t
(11~) with content of cadmium
(x) measured
at 300 “K.
tions and atmosphere of firin,.0 and hence different attendant cation distribution. It is clear that as the content of cadmium in the samples increases, /rs increases until it becomes maximum for a snmple with .u=O.3 and then falls to a minimum for further increase in cadmium. The cation distribution for lithium ferrite having inverse spine1 structure can be given as [ 141,
When non-magnetic divalent ions such as Zn’” and Cd’+ are substituted with a larger ionic radius, they tend to occupy tetrahedral sites by replacing Fe’+ ions since it is favoured by polarization effects. However. site preference of cations also depend upon their electronic configurations [ 151. Zn’+ and Cd’+ show a marked preference for tetrahedral sites where their 4s. 4P or 5s. 5P electrons. respectively, can form covalent bonds with 2P electrons of the oxygen ion. In light of the above considerations the cation distribution for our system can be written as
This leads us to conclude from Fig. 3 that Neel type of spin arrangement is favoured up to 30% cadmium content and the exchange quotient I;,,, = Ji,bSblJ&?~, < 3 /4. The fall of magnetization on addition of Cd beyond this limit cannot be explained on the basis of Neel’s two sublattice model, but instead on a three sublatticc model suggested by Yafet and Kittel [ 161. The interaction quotient I;,, for such an arrangement is > 3/4. On addition of cadmium. the cation distribution is not altered but Jcrh gets weakened while J,,)> goes through a change in its tendency from ferromagnetic to antiferromagnetic. Such an interpretation is supplemented by a gradual fall in the Curie temperature with an increase of Cd content as shown in Table 1 and as reported earlier [ 17 1. The maximum value of tip at 30% Cd pertains to the above change in tendency. The abrupt change in 4rMs and ~1~with composition would then correspond to a triangular arrangement of spins. The values of Y-K angles for samples with .V= 0 to 0.3 are zero (Table I ) indicating clearly that their magnetization can be explained on the basis of Neel’s two-sublattice model. The increase in Y-K angles with increase in content of cadmium above 30% suggests that the magnetization in these ferrites (x= 0.4 to 0.6) cannot be explained on the basis of the two sublattice model. However, the same can be explained on the basis of canted spin model. The rise of Y-K angles with the content of cadmium is indicative of the fact that the triangular spin is favoured in the B-site leading to the reduction in AB interaction. Though the B-B interactions are antiferromagnetic, the overall effect of A-B interaction prevails over
that of B-B interaction causing the spins on the B sites to become parallel to each other. Similarly, the presence of canted spins have been confirmed both experimentally and theoretically in the case of Cu-Zn ferrites [ 91.
4. Conclusions The lattice parameter increases monotonically with cadmium content. Both the bond lengths R, and RB increase with increase of cadmium content. The increase in R, with s can be associated with the increase in lattice parameter, while that of R, suggesting the decrease in iono-covalent character. The increase in magnetization up to .r= 0.3 can be explained on the basis of Neel’s two sublattice model, whereas the decrease of magnetization beyond s> 0.3 can be explained by using the three sublattice model.
Acknowledgements The authors are thankful to Professor R.N. Patil for helpful discussions and encouragement. One of the authors (B.K.C.) thanks the University Grants Commission (UGC), New Delhi for supporting this work.
References 111 J.S. I21 [31 [41 [51
[61 171 [Sl [91 [ 101
Baijal, S. Phanjoubam, D. Kothari, Solid State Commun. (USA). 83 (9) (1992)679-682. A. Ahmed. .I. Mater. Sci. (UK) 27 (15) (1992) 11201121. Y. Purushotham. N. Kumar. P. Kishon. P. Venugopal Reddy, Phys. Status Solidi A 148 ( 1995) K.17. S.A. Mazen, A.H. Walk, S.F. Mansour, J. Mater. Sci. 31 (1996) 26614665. D. Ravinder, T. Seshagiri Rao, Crystallog. Res. Technol. (East Germany) 25 (8) t 1990) 963-969. K. Radha, D. Ravinder, Ind. J. Pure Appl. Phys. 33 ( 1995) 7477. B.F. Levine, Phys. Rev. (USA) B7 ( 1973) 2591. S.R. Sawant. S.S. Suryavanshi, Curr. Sci. 57 ( 12) ( 1988). R.G. Kulkami, V.U. Patil, J. IMater. Sci. 17 ( 1972) 843. S.H. Patil, S.I. Path, SM. Kadam. S.R. Path, B.K. Chougule, Bull. Mater. Sci. 14 (5) (1991) 1225-1230. R.S. Path. P.K. Masker. S.V. Kakatkar. S.R. Jadhav, S.A. Patil. S.R. Sawant, J. Magn. Magn. Mater. 102 ( 1991) 5 l-55, P.N. Kamble. AS. Vainganker, Ind. J. Pure Appl. Phys. 28 ( 1990) 542-545. R.S. Path. S.V. Kakatkar, S.X. Path, A.M. Sankpal, S.R. Sawant, J. Mater. Chem. Phys. 28 ( 1991) 355-365. P. Venugopal Reddy. T. Seshagiri Rao, J. Less-Common Met. 75 (1980) 255. B. Vishwanathan. V.R.K. Murthy, Ferrite materials, Sci. Technol. ( 1990) 6-7. Y. Yafet, C. Kittel. Phys. Rev. 90 ( 1952) 295. N. Rezlescu. CR. Acad. Sci. Ser. B (Fr.) 270 (18) ( 1970) 1134.
ELSEVIER
Chrmibtry
and Physics 52 ( 1998)
166-169
Structural and magnetic properties of some mixed Li-Cd ferrites S.S. Bellad *, R.B. Pujar, B.K. Chougule h4oterials
S&me
Lnbomtorv,
Deparinwnt
of Pi+-isius,
Shivirji
University,
K01Imp:w
416004,
Indin
Received 3 June 1997: received in revised form 15 July 1997; accepted 20 August 1997
Abstract Polycrystalline L&Cd ferrites with the general formula Li,,,-,,, Cd,, Fe2,5--.r,204 are preparedby the standard ceramic technique. The Xray analysis reveals single phase formation of ferrite samples. The lattice parameter increases linearly with Cd’+ content, which can be attributed to ionic volume differences of the component cations involved. The bondlengths R, and R, increases as Cd content increases. The increase in bondlength R, with Cd content suggests that the iono-covalent character of the spine1 decreases. The magnetic moment (np) increases with Cd content up to s = 0.3, and then decreases with a further increase in X. The increase in magnetization can be explained on the basis of Neel’s two sublattice model whereas decrease in magnetization is attributed to the presence of a triangular arrangement of spins on 0 1998 Elsevier Science %A. the B-site and hence can be explained on the three sublattice model as suggested by Yafet and Kittel. Kqsrx~ds:
Magnetic
propcrtics;
Lithium
k&es;
Structural
properties
1. Introduction Lithium ferrites have become very altractive for microwave applications especially as a replacement for garnets owing to their low cost. Squareness of the hysteresis loop along with superior temperature performance due to a high Curie temperatureare other prominent properties that have tnade them very promising candidates for microwave devices. Several studieshave beenreportedwith the addition of divalent, trivalent and tetravalent ions in lithium ferrite [ l&4]. In fact, cadmium is substitutedto study a wide range of saturation magnetization values. Ravinder and Seshagiri Rao [S] studied the electrical and thermoelectric power of Li-Cd ferrites andfound n-type conduction. RadhaandRavinder [ 61 also studiedthe Li-Cd ferrites for their frequency andcompositionaldependenceof dielectric behaviour. However, no reports have beenfound in the literature regarding structural and magnetic properties in general and lattice parameter, bond lengths, saturation magnetization, Y-K anglesin particular in the mixed L&Cd ferrites sintered at 1000°C.Therefore in this communication,we report on compositional variation of lattice parameter.bond lengths,Bohr magneton,Curie temperatureetc. of Li-Cd ferrites. 2. Experimental The Li-Cd ferrite having the general formula Li0.5-s,2Fe,,,-,,zCd,rO, (where .u=O, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and * Corresponding
author.
OX&0584/98/$19.00 PII s0253-0584(97)02022-
0
1998 Ekvier 1
Science
S.A. All rights
reserved
0.7) were preparedby standardceramic technique usingAR grade oxides as starting materials.The oxides were mixed in stoichiometric proportions and the mixture was presintered at 750°C for 10 h. The resultant powder was used to make pellets (diameter= 1 cm, thickness= 0.3 cm) for magnetic hysteresisloop measurements,which were finally sinteredat 1000°Cfor 24 h and slowly cooledto room temperature.The final sintering temperaturewas fixed to 1000°Cby considering the volatility of lithium above this temperatureand to get fine particles. The completion of the solid state reaction wasconfirmed by X-ray diffraction studiescarried out on the powder sampleswith a PHILIPS PW-1710 diffractometer usingCuKol radiation (A = 1.5418A). All the samplesshow singlephaseformation.
3. Resultsand discussion Fig. 1 showsthe variation of lattice parametern with the content of cadmium in the presentL& -,,2Fe,,S -.~&d.~Ol ferrite system.It can be seenthat, with increasingthe content of cadmium, the lattice parameterincreasesmonotonically. The linear variation of lattice parameterwith the content of cadmium
shows that the system obeys the Vegard’s
law. This
be explained on the basisof the ionic volume differences between the comp?nent ions. Sinct the ionic radii of Cd’+ andLi ’ + are0.99 A [ 121and 0.70 A [ 131,respectively, and the content of Cd’+ increaseswhile that of Li’ + along with can
L67
8.*08
00 01
Fig. I. Variation
I 0.0
02
Ob
05
06
Cd CONTENT (X) of lattice parameter tz with content of cadmium
/ 0.1
I 0.2 Cd
Fig. 2. Variation
03
of bondlrngtha
I 0.3
I 04
CONTENT (X) -, (R,, R,) with content
the Fe3 + ions decrease, it is expected that the lattice parameter should increase with the cadmium substitution. Fig. 2 shows the compositional variation of bondlengths R, and R, with cadmium content. The bond lengths R, and R, were calculated using the relations
I 0.5
(s),
I 0.6
of cadmium
I
(1).
R,=aJ3(6+1/8)
(1)
R,=a(36’-6/2+1/16)“’
(2)
and 6= U-O.375 is the deviation from the u-parameter. The value of L[= 0.380 for pure lithium ferrite was taken. R, is
168 Table I Compositional Sr. No.
1 2 3
4 5 6 7
S.S. Beilod
variations
of different
et nl. /Muterials
Chemistq
52 (I 998) 166-169
parameters
Composition
Lattice parameter
Y-K
x
a ch 8.282
Lie J-h Lb J-b LL Lb, Lb
and Physics
sFez.s04 4sFe2.45Cdo ,04 J~~~~CCIO dh &%.&do 3% 3oFez.30C4 4, 25Fe2.&d0.50J d~dXd&
8.325 8.379 8.384
angles
4TrMs
Curie temperature
%I.
(G)
Perm.
0 0 0 0
3514
2.59
4214 4135 5176
3.20 3.65 3.79
350
502 402 327
4437
3.32
250
252
3548
2.79
152
2112
1.63
155 82
8.351
18"31'
8.487 8.523
35%
’
W36'
the shortest distance between A-site cation and oxygen ion and Rn is the shortest distance between B-site cation and oxygen ion. It is dear from Fig. 2 that both R, and RB increase linearly with content ofcadmium in the samples. The increase of average bondlength R, with Cd content can be associated with the increase in the lattice parameter. Since n increases with Cd content (Fig. 1)) the increase in R, with Cd content is anticipated. Levine [7], in his work on bond susceptibility in spinels, has shown that there exists an inverse relationship between the covalent character of spine1 and bond length. From Fig. 2 it is seen that as the content of Cd in the ferrite increases, the bond length RB also increases, indicating the decrease of iono-covalent character with increase of Cd content. Similar results have been reported by Sawant and Suryavanshi [ 81 in the case of the Cu-Zn ferrite system. From the high field hysteresis loop studies, the magneton numbers, i.e. the saturation magnetization per formula unit in Bohr magnetons, were calculated using the relation
I$=
Mol. WeightXSaturation 5585
690 52.5 395
Magnetization
np=(6Sx)cos
a,,-5(1-X)
Cd
Fig. 3. Variation
of Bohr magneton
80
(3)
(41
1 0.2
675
The variation of magnetic moment (no) with the content of cadmium is shown in Fig. 3. The trend observed is very much similar to the variation of np with composition in CuZn [9], Mg-Zn [ lo], Li-ZrZn [ 111 and Cd-Cu [ 121 ferrite systems. The value of Bohr magneton ( na) for Li-ferrite in our system is in good agreement with the earlier reported value 1:131. Whatever deviation exists may be due to porosity, defects introduced at the time of sintering, different condi-
1% 0 0.1
A.c. susc.
The experimentally determined values of Bohr magneton, Curie temperatures measured from initial permeability and a.c. susceptibility studies are given in Table 1, along with the calculated values of Yafet-Kittel (Y-K) angles using the relation
T 4.0 0-
0.0
(“C)
0.3 CONTENT(X)
04
C-5
0.6
_____t
(11~) with content of cadmium
(x) measured
at 300 “K.
tions and atmosphere of firin,.0 and hence different attendant cation distribution. It is clear that as the content of cadmium in the samples increases, /rs increases until it becomes maximum for a snmple with .u=O.3 and then falls to a minimum for further increase in cadmium. The cation distribution for lithium ferrite having inverse spine1 structure can be given as [ 141,
When non-magnetic divalent ions such as Zn’” and Cd’+ are substituted with a larger ionic radius, they tend to occupy tetrahedral sites by replacing Fe’+ ions since it is favoured by polarization effects. However. site preference of cations also depend upon their electronic configurations [ 151. Zn’+ and Cd’+ show a marked preference for tetrahedral sites where their 4s. 4P or 5s. 5P electrons. respectively, can form covalent bonds with 2P electrons of the oxygen ion. In light of the above considerations the cation distribution for our system can be written as
This leads us to conclude from Fig. 3 that Neel type of spin arrangement is favoured up to 30% cadmium content and the exchange quotient I;,,, = Ji,bSblJ&?~, < 3 /4. The fall of magnetization on addition of Cd beyond this limit cannot be explained on the basis of Neel’s two sublattice model, but instead on a three sublatticc model suggested by Yafet and Kittel [ 161. The interaction quotient I;,, for such an arrangement is > 3/4. On addition of cadmium. the cation distribution is not altered but Jcrh gets weakened while J,,)> goes through a change in its tendency from ferromagnetic to antiferromagnetic. Such an interpretation is supplemented by a gradual fall in the Curie temperature with an increase of Cd content as shown in Table 1 and as reported earlier [ 17 1. The maximum value of tip at 30% Cd pertains to the above change in tendency. The abrupt change in 4rMs and ~1~with composition would then correspond to a triangular arrangement of spins. The values of Y-K angles for samples with .V= 0 to 0.3 are zero (Table I ) indicating clearly that their magnetization can be explained on the basis of Neel’s two-sublattice model. The increase in Y-K angles with increase in content of cadmium above 30% suggests that the magnetization in these ferrites (x= 0.4 to 0.6) cannot be explained on the basis of the two sublattice model. However, the same can be explained on the basis of canted spin model. The rise of Y-K angles with the content of cadmium is indicative of the fact that the triangular spin is favoured in the B-site leading to the reduction in AB interaction. Though the B-B interactions are antiferromagnetic, the overall effect of A-B interaction prevails over
that of B-B interaction causing the spins on the B sites to become parallel to each other. Similarly, the presence of canted spins have been confirmed both experimentally and theoretically in the case of Cu-Zn ferrites [ 91.
4. Conclusions The lattice parameter increases monotonically with cadmium content. Both the bond lengths R, and RB increase with increase of cadmium content. The increase in R, with s can be associated with the increase in lattice parameter, while that of R, suggesting the decrease in iono-covalent character. The increase in magnetization up to .r= 0.3 can be explained on the basis of Neel’s two sublattice model, whereas the decrease of magnetization beyond s> 0.3 can be explained by using the three sublattice model.
Acknowledgements The authors are thankful to Professor R.N. Patil for helpful discussions and encouragement. One of the authors (B.K.C.) thanks the University Grants Commission (UGC), New Delhi for supporting this work.
References 111 J.S. I21 [31 [41 [51
[61 171 [Sl [91 [ 101
Baijal, S. Phanjoubam, D. Kothari, Solid State Commun. (USA). 83 (9) (1992)679-682. A. Ahmed. .I. Mater. Sci. (UK) 27 (15) (1992) 11201121. Y. Purushotham. N. Kumar. P. Kishon. P. Venugopal Reddy, Phys. Status Solidi A 148 ( 1995) K.17. S.A. Mazen, A.H. Walk, S.F. Mansour, J. Mater. Sci. 31 (1996) 26614665. D. Ravinder, T. Seshagiri Rao, Crystallog. Res. Technol. (East Germany) 25 (8) t 1990) 963-969. K. Radha, D. Ravinder, Ind. J. Pure Appl. Phys. 33 ( 1995) 7477. B.F. Levine, Phys. Rev. (USA) B7 ( 1973) 2591. S.R. Sawant. S.S. Suryavanshi, Curr. Sci. 57 ( 12) ( 1988). R.G. Kulkami, V.U. Patil, J. IMater. Sci. 17 ( 1972) 843. S.H. Patil, S.I. Path, SM. Kadam. S.R. Path, B.K. Chougule, Bull. Mater. Sci. 14 (5) (1991) 1225-1230. R.S. Path. P.K. Masker. S.V. Kakatkar. S.R. Jadhav, S.A. Patil. S.R. Sawant, J. Magn. Magn. Mater. 102 ( 1991) 5 l-55, P.N. Kamble. AS. Vainganker, Ind. J. Pure Appl. Phys. 28 ( 1990) 542-545. R.S. Path. S.V. Kakatkar, S.X. Path, A.M. Sankpal, S.R. Sawant, J. Mater. Chem. Phys. 28 ( 1991) 355-365. P. Venugopal Reddy. T. Seshagiri Rao, J. Less-Common Met. 75 (1980) 255. B. Vishwanathan. V.R.K. Murthy, Ferrite materials, Sci. Technol. ( 1990) 6-7. Y. Yafet, C. Kittel. Phys. Rev. 90 ( 1952) 295. N. Rezlescu. CR. Acad. Sci. Ser. B (Fr.) 270 (18) ( 1970) 1134.