Study of Mössbauer and magnetic properties of Al³⁺ ions doped superparamagnetic nano ferrites

Nanocrystalline Al³⁺ ions doped Mg_0.2Mn_0.5Ni_0.3Al_yFe_2-yO₄ compositions, where y=0.0 and 0.10 have been synthesized by citrate precursor method. Crystal structure and magnetic properties have been investigated at room temperature by means of X-ray diffraction, TEM, LCR meter, VSM and Mössbauer spectroscopy. Particle size and lattice parameter has been found to decrease as non-magnetic Al content increased. Relative loss factor has very low value in range of 10⁻⁶–10⁻⁵ which is three orders of magnitude less than samples prepared by conventional method. The Mössbauer spectroscopy results shows superparamagnetism. The isomer shift corresponding to Fe³⁺ ions do not show any significant variation which indicates that replacement of Fe³⁺ ions do not affect significantly the d-electrons density which in turn affects the s-electrons density around Fe³⁺ nuclei. The nuclear hyperfine magnetic fields have been found to decrease at A-site and B-site with increasing substitution of Al³⁺ ions in Mg-Mn-Ni ferrite