Role of secondary phases on the magnetic properties of MnFe2O4 nanoferrite studied at room and cryogenic temperatures: VSM, Mössbauer and FC-ZFC techniques

Abstract

MnFe₂O₄ nanoparticles synthesized by sol–gel auto-combustion method have been subjected to heat treatment in order to understand phase change in the sample. The XRD patterns indicated the ferrite phase with secondary phases. The experimental lattice parameter (a) of as-prepared and sintered sample was found to be 8.3603 and 8.3409 Å while average crystallite size (<D_XRD >) 9.3 and 15.7 nm. From FE-SEM micrographs, the nature of ferrite nanoparticles is nearly spherical and agglomerated into bigger particles with strong magnetic interactions. The particles are distributed in between 11–23 nm with an average particle size (<D_FE-SEM >) 16.6 nm. Mössbauer spectrum consists of three sextets including a paramagnetic doublet. The sextet having higher hyperfine field (H_hf) equal to 51.2 T with δ = 0.356 and Δ = 0.222 is assigned to the secondary phase of α-Fe₂O₃. The inversion parameter (λ) from the Mössbauer data is evaluated as 0.73. M−H loops indicated the soft magnetic nature of present ferrite system. The saturation magnetization (M_S) obtained is equal to 21 emu/g at 300 K and 41.4 emu/g at 5 K. The value of λ that fit to the M_S at 300 K is equal to 0.087. The blocking temperature (T_B) is evaluated as 153 K in the presence of 100 Oe while it is 72 K in the presence of 1000 Oe. The magnetocrystalline anisotropy of present nanoscaled Mn-ferrite is high and is equal to 2.2 × 10⁴ J/m³.