Multidomain to single-domain transition for uniform Co₈₀Ni₂₀nanoparticles

Abstract

Uniform fine Co80Ni20 particles with diameters between 18 and 540 nm have been synthesized by polyol reduction of metallic salts. Their magnetic properties have been studied as a function of the particle size at 10 and 300 K. From the analysis of the experimental results at room temperature, a transition from polydomain structure to single-domain structure with the reduction of the particle size to around 40 nm is deduced. A considerable decrease of the saturation magnetization with respect to the bulk value has been found as the particle size decreases at both measuring temperatures. At low temperature, a strong increase of coercivity has been observed which is ascribed to an enhancement of the effective magnetic anisotropy induced by the surface layer.