Magnetic studies of Mn2+substituted Zn-ferrite nanoparticles: Role of secondary phases, bond angles and magnetocrystalline anisotropy

Magnetic studies of MnxZn1-xFe2O4 (x = 0.5, 0.6, 0.7) nanoferrite particles prepared by sol-gel auto combustion method are presented. The deviation of the oxygen positional parameter (U) from the ideal value of 0.375 is an indicator for the cation redistribution in the present ferrite systems. The variation of bond angles estimated from the cation distribution seemed to be strengthening of A-B superexhange interaction. The nature of M - H loops revealed that the present ferrite nanoparticles are in the single domain state showing superparamagnetism. The saturation magnetization (Ms) increases while coercivity (Hc) decreases with the substitution of Mn2+ ion concentration. The highest value of Ms = 25 emu/g was reported for the composition x = 0.7. It was observed that the blocking temperature (TB) is decreasing and again increasing with the doping level of Mn2+. From FC-ZFC curves, the uneven variation of magnetization (M) at 10 K can be found. It attributes to the cation distribution in the ferrite samples at 10 K is different from those of at 300 K. The Mossbauer spectra revealed that the ferrite nanoparticles exhibited both quadruple and hyperfine interactions can be found in the composition x = 0.7 while the ferrite nanoparticles exhibited that only quadruple interaction can be in the compositions x = 0.5 and 0.6. The isomer shift (delta) values showed the presence of high spin Fe3+ ions only. The paramagnetic doublets having higher value of quadruple splitting (Delta) are assigned to the core structure while doublets lower value of quadruple splitting (Delta) is assigned to shell structure. The present results are incorporated in terms of cation distribution, magnetocrystalline anisotropy considering the core-shell morphology of ferrite nanoparticles.