Abstract
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.
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