Enhancement of the magnetic properties of Ni-Cu-Zn ferrites with the substitution of a small fraction of lanthanum for iron

The effect of lanthanum ion substitution for iron on the structural and magnetic properties of Ni-Cu-Zn ferrite is reported. The (Ni_0.25Cu_0.20Zn_0.55)La_xFe_2−xO₄ ferrite compositions with x = 0.0, 0.025, 0.050 and 0.075, were synthesized by nitrate-citrate auto-combustion route. Rietveld structure refinement was carried out to evaluate; La solubility in spinel, residual stress in sintered core, quantity of secondary LaFeO₃ phase formed and change in lattice parameters, etc. Density, crystallite size, grain size, residual macrostress and initial permeability were directly affected by the substitution. A significant increase in initial permeability was achieved by a small fraction of La substitution. The La solubility in the Ni-Cu-Zn ferrite lattice was found very low (∼0.1 atom/unit cell). Co-relations between magnetic properties and measured physical/structural properties were discussed.