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Cation distribution and curie temperature in the copper-manganese-zinc ferrites
1096
TECHNICAL NOTES
REFERENCES 1. BLOEMBERGEN N. Report of the Conference on Defects in Crystalline Solids, Bristol 1954, p. 1. London: The Physical Society (1955). 2. COLLOTTI G., CONTI L. G. and ZOCCHI M., Acta crystallogr. 12, 416 (1959). 3. CONTI L. G., D ' A L E S S A N D R O R. and DI NAPOLIV., J. Phys. Chem. Solids. To be published (1971). 4. CRANK J., The Mathematics o f Diffusion, pp. 88-91. Oxford University Press, London (1956). 5. KOLTHOFF I. M. and BOWERS R. C., J. Am. chem. Soc. 76, 1503, 1510 (1954). 6. KOLTHOFF 1. M. and EGGERTSEN F. T., J.Am. chem. Soc. 63, 1412 (1941). 7. KOLTHOFF I. M. and O'BRIEN A. S., J. Am. chem. Soc.61, 3409, 3414 (1939). 8. LANGER A.,J. chem. Phys. U, 11 (1943). 9. POUND R. V., Prog. nucl. Phys. 2, 21 (1952). 10. POUND R. V. and KNIGHT W. D., Rev. scient. lnstrum. 21, 219 (I 950). 11. REIF F., Phys. Rev. I00, 1597 (1955). 12. SPOKAS J. J. and SLICHTER C. P., Phys. Rev. 113, 1462 (1959). 13. TANNHAUSER D. S., J. Phys. Chem. Solids 5, 224 (1958). 14. WATK1NS G. D. and POUND R. V., Phys. Rev. 82, 343 (1951).
J. Phys. Chem. Solids
Vol. 32, pp. 1096-1097.
Cation distribution and Curie temperature in the copper-manganese-zinc ferrites (Received I OJuly 1970)
WE have previously investigated the influence of cation distribution on the Curie point of the copper-zinc ferrites[1]. In the present note, some preliminary results concerning this problem for copper-manganese-zinc ferrites are discussed. The samples, of toroidal shape, were prepared from oxides by usual ceramic techniques. Sintering in air at 1200~ for 4 hr was followed by quick cooling. X-ray and chemical analyses, carried out after sintering, showed only the presence of a spinel phase with a small deviation from the initial chemical composition. The Curie temperature was determined from the temperature dependence of the saturation magnetization, with a precision of 1-2~ The cation distribution was
modified by thermal treatment in an oxygen atmosphere. Results obtained for two samples of three compositions are shown in the Table. Because the sintering temperature is higher than 950~ where the reduction of Cu 2+ to Cu '§ ions begins [2], the number of Cu 1§ ions at the end of the sintering p,rocess is large. Assuming that Cu 1+ ions have a certain preference for the tetrahedral sites, this fact accounts for a lowering of the Curie temperature[l]. The oxidation of Cu ~+--> Cu ~+ ions involves movement of the copper ions from the tetrahedral to the octahedral sites since Cu 2+ ions prefer octahedral sites[3]. This will result in an increase in the Curie temperatures. At the same time with the migration of copper ions from tetrahedral to octahedral sites, an inverse migration of Fe 3+ ions takes place. Oxidation of Cu 1+ ions in the sintered samples was accomplished by an oxygen treatment followed by rapid cooling. As can be seen in the Table the Curie point does in fact shift to higher temperatures after this treatment. After an analogous nitrogen treatment however, the Curie point does not change since in an inert atmosphere oxidation cannot take place. The change in Curie point after oxygen treatment, for copper-manganese-zinc ferrites, is less pronounced in comparison with the copper-zinc ferrites[1]. We explain this fact in the following way. In the coppermanganese-zinc ferrites, on the tetrahedral sites there are Cu ~+, Mn 2+, Zn z+ and Fe 3+ ions, and on the octahedrai sites there are Cu z+, Mn 3§ Fe ~+ and F e 3+ ions (Mn 3+ ions on the octahedral sites are present due to the existence of Fe ~+ ions on these sites [4]; the Fe 2+ ions result from the reduction Fe 3+ --> Fe 2+ in the sintering process due to the evaporation of zinc at the ferrite surface[5]). In the oxidation process, as a result of the oxidation Fe z+ ---> Fe 3+, migration of manganese ions from octahedral to tetrahedral sites takes place; this causes a small decrease in the Curie temperatures.
TECHNICAL
The passage of copper ions from the tetrahedral to the octahedral sites in the oxidation process, accompanied by an inverse passage of the Fe 3+ ions (or of Mn 2+ ions), has been proved by saturation magnetization measurements.
NOTES
1097
zation of this lattice. This fact is responsible for the decrease in magnetization of the ferrites. The substitution of Fe 3+ ions by Cu ~+ ions on the octahedral lattice, decreases the magnetization of this lattice, having a similar effect upon the magnetization of the ferrite.
Table 1. Initial chemical composition, Curie temperature (To) and saturation magnetization (Js) for the ferrites studied sintering in air Initial chemical composition Cuo.2Mno.zZno,rFe~O4 Cu0,~Mno.aZn0.4Fe~O4 Cuo.ssM no,~sZnoa Fez O4
(1200~ Tc (*C) 45 43 158 162 268 273
treatment in 02
f o r 4 h r ) (1000~ Js Tc (Gs/g) (~ 398 389 276 273 183 179
In the Table, the saturation magnetizations, measured at 77~ for three of the samples studied are shown. We observe that the saturation magnetization decreases in the oxidation process but does not change in the nitrogen treatment. Because the magnetization of ferrites is determined by the difference between the magnetizations of octahedral and tetrahedral lattices, the substitution of Cu 1+ ions (which have no magnetic moment) by the Fe a+ ions (which have a magnetic moment) on the tetrahedral lattice, increases the magneti-
66 -193 -310 --
treatment in N f o r 2 hr)
for 2 hr) (1000~ -/8 Tc (Gs/g) (~ 369 -234 -112 --
-43 -165 -271
Js (Gs/g) -387 -269 -181
Research Center of Physics, lassy, Romania
N. R E Z L E S C U E. C U C I U R E A N U
REFERENCES 1. R E Z L E S C U N. and C U C I U R E A N U E., C. R.Acad. Sci. Paris 269, 952 (1969). 2. S T I E R S T A D T K., B E N Z H. and R E C H E N B E R G H., Proc. Int. Conf. Magnetism, N o t t i n g h a m , p. 609 (1964). 3. O H N I S H I H. a n d T E R A N I S H I T., J. phys. Soc. Japan 16, 33 (!961). 4. MILLERA.,Phys. Rev. 116, 1481 (1959). 5. S M I T J. a n d W l J N H. P. J., Les Ferrites, Bibl. Tech. Philips, Dunod, Paris ( 1961 ).
TECHNICAL NOTES
REFERENCES 1. BLOEMBERGEN N. Report of the Conference on Defects in Crystalline Solids, Bristol 1954, p. 1. London: The Physical Society (1955). 2. COLLOTTI G., CONTI L. G. and ZOCCHI M., Acta crystallogr. 12, 416 (1959). 3. CONTI L. G., D ' A L E S S A N D R O R. and DI NAPOLIV., J. Phys. Chem. Solids. To be published (1971). 4. CRANK J., The Mathematics o f Diffusion, pp. 88-91. Oxford University Press, London (1956). 5. KOLTHOFF I. M. and BOWERS R. C., J. Am. chem. Soc. 76, 1503, 1510 (1954). 6. KOLTHOFF 1. M. and EGGERTSEN F. T., J.Am. chem. Soc. 63, 1412 (1941). 7. KOLTHOFF I. M. and O'BRIEN A. S., J. Am. chem. Soc.61, 3409, 3414 (1939). 8. LANGER A.,J. chem. Phys. U, 11 (1943). 9. POUND R. V., Prog. nucl. Phys. 2, 21 (1952). 10. POUND R. V. and KNIGHT W. D., Rev. scient. lnstrum. 21, 219 (I 950). 11. REIF F., Phys. Rev. I00, 1597 (1955). 12. SPOKAS J. J. and SLICHTER C. P., Phys. Rev. 113, 1462 (1959). 13. TANNHAUSER D. S., J. Phys. Chem. Solids 5, 224 (1958). 14. WATK1NS G. D. and POUND R. V., Phys. Rev. 82, 343 (1951).
J. Phys. Chem. Solids
Vol. 32, pp. 1096-1097.
Cation distribution and Curie temperature in the copper-manganese-zinc ferrites (Received I OJuly 1970)
WE have previously investigated the influence of cation distribution on the Curie point of the copper-zinc ferrites[1]. In the present note, some preliminary results concerning this problem for copper-manganese-zinc ferrites are discussed. The samples, of toroidal shape, were prepared from oxides by usual ceramic techniques. Sintering in air at 1200~ for 4 hr was followed by quick cooling. X-ray and chemical analyses, carried out after sintering, showed only the presence of a spinel phase with a small deviation from the initial chemical composition. The Curie temperature was determined from the temperature dependence of the saturation magnetization, with a precision of 1-2~ The cation distribution was
modified by thermal treatment in an oxygen atmosphere. Results obtained for two samples of three compositions are shown in the Table. Because the sintering temperature is higher than 950~ where the reduction of Cu 2+ to Cu '§ ions begins [2], the number of Cu 1§ ions at the end of the sintering p,rocess is large. Assuming that Cu 1+ ions have a certain preference for the tetrahedral sites, this fact accounts for a lowering of the Curie temperature[l]. The oxidation of Cu ~+--> Cu ~+ ions involves movement of the copper ions from the tetrahedral to the octahedral sites since Cu 2+ ions prefer octahedral sites[3]. This will result in an increase in the Curie temperatures. At the same time with the migration of copper ions from tetrahedral to octahedral sites, an inverse migration of Fe 3+ ions takes place. Oxidation of Cu 1+ ions in the sintered samples was accomplished by an oxygen treatment followed by rapid cooling. As can be seen in the Table the Curie point does in fact shift to higher temperatures after this treatment. After an analogous nitrogen treatment however, the Curie point does not change since in an inert atmosphere oxidation cannot take place. The change in Curie point after oxygen treatment, for copper-manganese-zinc ferrites, is less pronounced in comparison with the copper-zinc ferrites[1]. We explain this fact in the following way. In the coppermanganese-zinc ferrites, on the tetrahedral sites there are Cu ~+, Mn 2+, Zn z+ and Fe 3+ ions, and on the octahedrai sites there are Cu z+, Mn 3§ Fe ~+ and F e 3+ ions (Mn 3+ ions on the octahedral sites are present due to the existence of Fe ~+ ions on these sites [4]; the Fe 2+ ions result from the reduction Fe 3+ --> Fe 2+ in the sintering process due to the evaporation of zinc at the ferrite surface[5]). In the oxidation process, as a result of the oxidation Fe z+ ---> Fe 3+, migration of manganese ions from octahedral to tetrahedral sites takes place; this causes a small decrease in the Curie temperatures.
TECHNICAL
The passage of copper ions from the tetrahedral to the octahedral sites in the oxidation process, accompanied by an inverse passage of the Fe 3+ ions (or of Mn 2+ ions), has been proved by saturation magnetization measurements.
NOTES
1097
zation of this lattice. This fact is responsible for the decrease in magnetization of the ferrites. The substitution of Fe 3+ ions by Cu ~+ ions on the octahedral lattice, decreases the magnetization of this lattice, having a similar effect upon the magnetization of the ferrite.
Table 1. Initial chemical composition, Curie temperature (To) and saturation magnetization (Js) for the ferrites studied sintering in air Initial chemical composition Cuo.2Mno.zZno,rFe~O4 Cu0,~Mno.aZn0.4Fe~O4 Cuo.ssM no,~sZnoa Fez O4
(1200~ Tc (*C) 45 43 158 162 268 273
treatment in 02
f o r 4 h r ) (1000~ Js Tc (Gs/g) (~ 398 389 276 273 183 179
In the Table, the saturation magnetizations, measured at 77~ for three of the samples studied are shown. We observe that the saturation magnetization decreases in the oxidation process but does not change in the nitrogen treatment. Because the magnetization of ferrites is determined by the difference between the magnetizations of octahedral and tetrahedral lattices, the substitution of Cu 1+ ions (which have no magnetic moment) by the Fe a+ ions (which have a magnetic moment) on the tetrahedral lattice, increases the magneti-
66 -193 -310 --
treatment in N f o r 2 hr)
for 2 hr) (1000~ -/8 Tc (Gs/g) (~ 369 -234 -112 --
-43 -165 -271
Js (Gs/g) -387 -269 -181
Research Center of Physics, lassy, Romania
N. R E Z L E S C U E. C U C I U R E A N U
REFERENCES 1. R E Z L E S C U N. and C U C I U R E A N U E., C. R.Acad. Sci. Paris 269, 952 (1969). 2. S T I E R S T A D T K., B E N Z H. and R E C H E N B E R G H., Proc. Int. Conf. Magnetism, N o t t i n g h a m , p. 609 (1964). 3. O H N I S H I H. a n d T E R A N I S H I T., J. phys. Soc. Japan 16, 33 (!961). 4. MILLERA.,Phys. Rev. 116, 1481 (1959). 5. S M I T J. a n d W l J N H. P. J., Les Ferrites, Bibl. Tech. Philips, Dunod, Paris ( 1961 ).