Model of the magnetization of nanocrystalline materials at low temperatures

Abstract

A theoretical model incorporating the material texture has been developed to simulate the magnetic properties of nanocrystalline materials at low temperatures where the effect of thermal energy on magnetization is neglected. The method is based on Landau-Lifshitz-Gilbert (LLG) theory and it describes the magnetization dynamics of individual grains in the effective field. The modified LLG equation incorporates the intrinsic fields from the intragrain magnetocrystalline and grain boundary anisotropies and the interacting fields from intergrain dipolar and exchange couplings between the neighbouring grains. The model is applied to study magnetic properties of textured nanocrystalline Ni samples at 2K and is capable to reproduce closely the hysteresis loop behaviour at different orientations of applied magnetic field. Nanocrystalline Ni shows the grain boundary anisotropy constant K1s=−6.0×104J/m3 and the intergrain exchange coupling denoted by the effective exchange constant Ap = 2.16 × 10–11 J/m. Analytical expressions to estimate the intergrain exchange energy density and the effective exchange constant have been formulated.