Particle size effects on magnetic properties of BaFe12−2<i>x</i>Ti<i>x</i>Co<i>x</i>O19 fine particles

Abstract

Particle size effects on magnetic properties of BaFe12−2xTixCoxO19 fine particles were investigated. Saturation magnetization of these particles decreased with decreasing particle size. This result can be explained with the existence of a nonmagnetic thin layer, several angstroms in thickness, on the surface of the particles. Particle size dependence of coercivity for these particles, below 1000 Å in size, follows the superparamagnetism theory. For the decrease in coercivity above 2000 Å, multidomain nucleation is inferred as one of the possible mechanisms. Particle shape dependence of coercivity is well explained with the coherent rotation model, considering shape anisotropy.