Grain boundary anisotropy on nano-polycrystalline magnetic thin films

Grain boundaries in polycrystalline thin films with crystallite sizes at nanoscale presents regions characterized by a high degree of local structural disorder. As a consequence, great values of the associated local anisotropies are expected. On this regard, a systematic investigation of the effect of the grain boundary anisotropy on the magnetic properties in such type of nanostructured systems is addressed. For developing this work, a standard Monte Carlo simulation in the framework of classical Heisenberg spins was carried out, with a Hamiltonian involving exchange couplings, dipolar interactions, Zeeman interaction and contributions of cubic magneto-crystalline anisotropy. A quantification of local structural disorder was considered. Results revealed that i) by keeping the same number of grains, different organizations give rise to different spontaneous magnetizations, ii) the critical exponent of the magnetization differs of pure models, which is attributed to the complexity of the lattice and consistent with a distribution of critical temperatures, iii) Boundary anisotropy varies with temperature and its strength are determinant factors for blocking temperatures, and iv) Boundary anisotropy inside in the hysteretic properties where coercive field variations are observed.