Effect of particle size distribution on the structure, hyperfine, and magnetic properties of Ni_(0.5)Zn_(0.5)Fe_2O_4 nanopowders

摘要

Ni_(0.5)Zn_(0.5)Fe_2O_4 nano powders were synthesized by an auto combustion method and then 'heat treated at different temperatures in air for a fixed time. As a consequence, a distribution in particle size and strain was incorporated within the specimens, as estimated from the Rietveld refinement analysis of the powder x-ray diffraction data. The changes in the microstructure and crystal structure parameters were carefully extracted through the refinement analysis. Thermal annealing causes increment in the dispersion and mean of the size distribution. Reallocation of cations in the lattice sites occur as a consequence of the heat treatment which was manifested in their altered unit cell length (a), r.m.s. strain (〈ε~2〉~(1/2)), oxygen positional parameter (u), metal-oxygen bond lengths (R_(OA) and R_(OB)), and the band positions (v_1 and v_2) in the vibrational spectroscopy. We also investigate the hyperfine and magnetic properties of the samples using different instrumental techniques (with different operating time scales) like Mossbauer spectroscopy, electron paramagnetic resonance spectroscopy, and superconducting quantum interference device magnetometry. Results show that the effect of particle size distribution was manifested in their hyperfine field distribution profile, paramagnetic resonance spectra, and magnetic anisotropy energy distribution profile. Co-existence of superparamagnetic and ferrimagnetic phase was recorded at room temperature in the samples when annealed at lower temperature. However, with increase in annealing temperature, the nature of the size distribution changes and ferrimagnetic ordering predominates for the larger size nano-particles. Thus, the effect of particle size distribution on the structural, hyperfine, and magnetic properties of various Ni_(0.5)Zn_(0.5)Fe_2O_4 nanoparticles was investigated herein which hitherto has not been discussed in the literature.