Magnetization and configurational anisotropy in magnetic clusters: Monte Carlo simulation

Based on the Monte Carlo simulation, the magnetic properties of the clusters, e.g. magnetization, Curie temperature, hysteresis, coercivity, natural angle and energy distribution etc., have been calculated. It has been found that, for the pure ferromagnetic cluster, the T <Superscript>3/2</Superscript> Bloch law is well satisfied at low temperature (T > 0.5 T <Subscript> C </Subscript>) and B <Subscript> sur </Subscript> is equal to 3 B <Subscript> bulk </Subscript>. Meanwhile, there are clear indications that B increases drastically with the reducing atomic number Nwhich is consistent with the experimental facts. The results have been evalucted using the Bloch exponent law in the approximate crystalline approximation. It has also been demonstrated that the size dependence of the Curie temperature can be described by finite-size scaling theory. The investigation of the hysteresis and the spin configurations in different magnetization processes reveals the existence of an easy magnetization direction and anisotropy. The thermal coercivity for the clusters with zero and finite uniaxial anisotropy matches the experimental results well. The simulated results for the natural angle and energy distribution in the clusters prove further the existence of the configurational anisotropy in the clusters. It has been discussed that the natural angle and energy distribution influence the hysteresis of a cluster. Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2004