Magnetic relaxation in Zn-Sn-doped barium ferrite nanoparticles for recording

Abstract

Magnetic relaxation analysis has been carried out on Zn-Sn-doped barium ferrite BaFe12-2xZnxSnxO19 nanoparticles with 0 ≤ x ≤ 0.5 at room temperature. The choice of these two ions combination was based on the consideration that Zn2+ substitution could help to increase saturation magnetization Ms and Sn4+ substitution could decrease the temperature dependence of coercivity dHc/dT. Logarithmic behavior on the time dependence of the magnetization for these particles has been observed. The measured viscosity coefficient S was found to vary with the applied field and peaked around the coercive field Hc. With increased doping concentration x, thermal relaxation of magnetization increased, mainly due to the decrease of particle size and anisotropy field, as well as their wider distributions. The activation volume Vac and fluctuation field Hf were determined from the magnetic viscosity coefficient S together with the irreversible magnetic susceptibility χirr. Vac was found to be smaller than the particle's physical volume, indicating incoherent magnetic reversals in these particles.