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

Magnetic relaxation analysis has been carried out on Zn-Sn-doped barium ferrite BaFe12-2xZnxSnxO19 nanoparticles with 0 less than or equal to x less than or equal to 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 M-s and Sn4+ substitution could decrease the temperature dependence of coercivity dH(c)/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 H-c. 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 V-ac and fluctuation field H-f were determined from the magnetic viscosity coefficient S together with the irreversible magnetic susceptibility chi(irr). V-ac was found to be smaller than the particle's physical volume, indicating incoherent magnetic reversals in these particles. (C) 2000 Elsevier Science B.V. All rights reserved.