Mössbauer spectroscopic studies of Al3+ ions substitution effects in superparamagnetic Mg0.2Mn0.5Ni0.3AlyFe2−yO4 compositions

Nanoparticles of Al3+ ions substituted MgMnNi materials with compositions Mg0.2Mn0.5Ni0.3AlyFe2−yO4 (y = 0.15-0.25) were synthesized by citrate precursor technique. Samples were characterized by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and room temperature 57Fe Mössbauer spectroscopy. Saturation magnetization decreases with increasing Al3+ ions concentration because replacement of Fe3+ ions by Al3+ ions at octahedral B-site weaken sublattice interaction and lowers magnetic moments. Mössbauer spectral studies show that as-prepared nano-sized samples are superparamagnetic at room temperature. Superparamagnetic relaxation was observed for small crystallite in samples with higher Al content, which is attributed to weakening of A-B exchange interaction. Mössbauer spectra at 300 K show a gradual collapse of magnetic hyperfine splitting typical for superparamagnetic relaxation. An increase in inversion parameter is observed with increasing Al3+ ions substitution, which is attributed to decrease in crystallite size.