Infrared spectroscopic and electron paramagnetic resonance studies on Dy substituted magnesium ferrite

Dysprosium substituted magnesium ferrite with composition MgDy _xFe_2-xO₄ with 0.00≤x≤0.07 synthesized by the solid state reaction technique was subjected to Fourier transform infrared spectroscopy and electron paramagnetic resonance studies. Infrared spectrum analysis were carried out to confirm the spinel phase formation and to ascertain the cation distribution in the ferrite phase. The absorption spectra show two significant absorption bands between 400 and 1000 cm^-1 which are attributed to tetrahedral (A) and octahedral (B) sites of the spinel phase. The positions of bands were found to be composition dependent. Splitting of bands as well as appearance of shoulders shows the presence of Fe²⁺ ions in the system. The force constants for tetrahedral and octahedral sites were calculated and found to vary with Dy³⁺ ions content. Electron paramagnetic resonance spectra of these samples exhibit broad, asymmetric resonance signal due to Fe³⁺/Dy³⁺ ions present in the host lattice. The spectra become broader with Dy³⁺ ions substitution in pure Mg-ferrite and this broadening is attributed to surface spin disorder (spin frustration) possibly coming from mainly antiferromagnetic interactions between the neighbouring spins in the magnetic grains. The weak superexchange interactions results in the broadening of the resonance line width and large g-value as compared to the free electron value.