Study on magnetic and hyperfine properties of mechanically milled Ni0.4Zn0.6Fe2O4 nanoparticles

Abstract Herein, we report a comprehensive and comparative study on the structural, microstructural, magnetic and room temperature hyperfine properties of nanosized Ni 0.4 Zn 0.6 Fe 2 O 4 having particle sizes 48 (S1), 21 (S2) and 15 (S3) nm synthesized by high energy ball milling method. All the samples are characterized by powder X-ray diffraction, transmission electron microscopic, field emission scanning electron microscopic and Mossbauer spectroscopic techniques. S1, S2 and S3 are single phase nanosized cubic spinel ferrites of Fd-3m symmetry with lattice parameter 8.39, 8.41 and 8.44 A, respectively, and the samples consist of particles having assorted size and nearly spherical shape. The constituent particles of S1 exhibit multi domain magnetic structure. It shows collective magnetic behavior and clear hysteresis loop at 300 K with coercive field of 140 Oe. On the other hand, S2 and S3 are composed of particles with single domain magnetic configuration and these samples show purely superparamagnetic behavior above their blocking temperature (T B ). All the samples display magnetic ordering at low temperature. The values of T B of S2 and S3 are 250 and 185 K, respectively. The values of saturation magnetization (M SAT ) of S1, S2 and S3 at 300 K are 47, 42, 30 emu/g, at 150 K are 58, 50, 43 emu/g and at 10 K are 86, 72, 56 emu/g, respectively. The values of coercivity of S1, S2 and S3 at 150 K are 280, 400, 350 Oe and at 10 K are 1600, 2800 and 2000 Oe, respectively. It has been shown that for mechanically activated nanosized Ni 0.4 Zn 0.6 Fe 2 O 4 the values of M SAT decrease with the reduction of particle size due to surface spin canting effect, the coercivity is determined by the magnetic domain structure of the particles in the samples, cation distribution can be reliably estimated through infield Mossbauer spectroscopic study and field dependent dc magnetization measurement in conjugation and the particles in S2 are comprised of ferrimagnetically aligned core surrounded by surface region having highly noncollinear spin structure. The sample S2 exhibits memory effect in its dc magnetization recorded as a function of temperature, which may be utilized in fabrication of magnetic storage devices.