Influence of rare-earth ions on the structure and magnetic properties of barium W-type hexaferrite

Barium W-type hexaferrite with composition Ba_0.95R_0.05Mg_0.5Zn_0.5CoFe₁₆O₂₇ where R=Y, Er, Ho, Sm, Nd, Gd, and Ce ions has been prepared by the double-sintering ceramic technique. Structure of the prepared samples has been characterized by the X-ray diffraction (XRD) technique. The XRD patterns at room temperature show the presence of secondary phase with the intensity of the secondary phase increasing with increasing ionic radius of the rare earth (RE) ions. The variation of the magnetic susceptibility (χ_M) with temperature in the range 300–750 K at different magnetic field intensities (1280, 1733 and 2160 Oe) was studied by using Faraday's method. The results show that the Curie temperature (T_C) increases regularly with increasing RE ionic radius then decreases again, after which it reaches maximum value at Sm ion of radius ≈1.04 Å. This behavior was explained on the basis of the changes in Fe³⁺–O–Fe³⁺ superexchange interaction. The effective magnetic moment μ_eff. of the investigated samples was discussed in view of varying the RE element as well as the magnetization of different sublattices.