CATION DISTRIBUTION AND MAGNETIC PROPERTIES OF FERRITES

A series of spinel ferrites i.e. Cu1-xZnxFe2O4, Mn1-xCuxFe2O4, Mg1-xNixFe2O4 and Ni0.65 Zn0.35 CuxFe2-x O4 with X=0,0.25, 0.50, 0.75 and 1.0 were prepared, to study the relationship between structural parameters and concentration of the substituted magnetic (Cu, Ni) and non magnetic, (Zn) ions, by standard ceramic method. By determining crystal structure, oxygen positional parameter and cation distribution using X-ray diffraction and R-factor method revealed that these ferrites belong to the family of mixed or partially inverse spinels. On the magnetic properties.\ud \ud A systematic AC magnetic susceptibility measurement by mutual inductance technique has been employed to measure Curie temperature, effective magnetic moments, g-values. The paramagnetic Curie temperature has also been measured to calculate the strength of the dominant exchange interaction as a function of concentration of the substituted ions in these mixed ferrites. The dominant interaction in all ferrite system is A-B interaction which is due to the negative values of paramagnetic Curie temperature O(K) and the distribution of cations among A and B sites showing that the magnetic ordering is antiferromagnetic. The 1/X vs T relationships confirm the Neel type behaviour of antiferromagnetic ordering in these ferrites. The Curie temperature (Tc) rises for certain concentrations, possibly due to increase in exchange interaction and magnetic moments. The compositional variation and the site preference analysis show weakening of A-B interaction due to the presense of triangular spin arrangements of Y-K type on B-sublattice.\ud \ud The variation of saturation magnetization, remanance and coercivity, with different concentration were studied using M-H loops. The increase in saturation magnetization (Ms) and remanance (Mr) observed for addition of divalent metal ions is due to strong exchange interaction, magnetic moments and high packing density. Beyond certain concentration a decreasing trend in the intrinsic magnetic properties corresponds to the decrease in exchange interaction, magnetic moments and the presence of Y-K angles in ferrites.\ud \ud A systematic study of the change in resistivity with the application of magnetic field (magnetoresistance) both longitudinal and transverse, has been carried out to optimize the highest resistive state for specific applications. The variation in magnetoresistance is of the first order effect, as in semiconductors except as in semiconductors except MgNi-ferrite in which the effect is not observed due to low concentration of magnetic moments.\ud \ud From microstructure analysis, the coercivity Hc is dependent on grain size. The deviation from linear relationship for coercivity (Hc) and porosity (p) can be related to the variation of exchange interaction, magnetic moments and the redistribution of cations on tetrahedral and octahedral sites due to addition of divalent metal ions