Onsite magnetic moment through cation distribution and magnetocrystalline anisotropy studies in NiFe_2−xR_xO₄ (R = Y and Lu; x = 0, 0.05, and 0.075)

Onsite magnetic moments through cation distribution and magnetocrystalline anisotropy studies of NiFe_2−xR_xO₄ (R = Y and Lu; x = 0, 0.05, and 0.075) compounds were investigated, and the results are discussed and presented in this paper. All the compounds were prepared by solid state reaction, and the compounds formed in the cubic inverse spinel phase with the space group $Fd3¯m$⁠. The cation distribution, bond lengths, u-parameter, etc. were estimated through the Rietveld refinement of XRD patterns. Increment in the lattice constant was observed upon partial substitution of Fe³⁺ by Y³⁺/Lu³⁺. The presence of all elements and their ionic states were confirmed from X-ray photoelectron spectroscopy studies. Analyses of Mössbauer spectra revealed that the hyperfine fields and the magnetic moments at the B-site (and hence net moment) decreased with increasing Y³⁺/Lu³⁺ occupancy and that the compounds exhibited a Néel-type, collinear ferrimagnetic structure. Magnetization measurements revealed that the magnetic moment decreased with Y³⁺/Lu³⁺ substitution. The high field regimes of the magnetization curves were modeled using the law of approach to the saturation magnetization equation, and the first order cubic anisotropy constants (K₁) were calculated. The temperature variation of K₁ and effects of Y³⁺/Lu³⁺ substitution are explained.