STRUCTURAL, IR AND MAGNETIZATION STUDIES ON LA3+ SUBSTITUTED COPPER FERRITE

The ferrites of the composition CuLa2xFe2-2xO4 prepared by ceramic method exhibited spinel phases for X upto 0.4 whereas for x > 0.4 the mixed phases of spinel and pervoskite were observed. For spinel phase x < 0.4 the lattice constants both a and c decrease with increase of x while for x > 0.4 the lattice constants of spinel phase increase and remain constant. The pervoskite phase has been identified to be that of La2CuO4. The compositional variation of magnetisation shows decrease of n(B) with the increase of x. However, the samples with x = 0.6 do not exhibit net magnetisation. The Curie temperature shows decrease with x for upto 0.4 while for x = 0.4 Curie temperature increases and remains invariant. This constant value of T(c) is nearly equal to the Curie point for pure copper ferrite. The variation of magnetisation has been discussed on the basis of AB interaction and migration of Cu, Fe to A site from B site. La goes to B site only. The I.R. spectra reveal two extra prominent bonds for x = 0.4. The change in the force constants is explained by considering the oxygen vacancies and La ions on B site.