Monte Carlo Simulation for Magnetic Domain Structure and Hysteresis Properties

Abstract

Recently many studies for magnetic process simulations of micro magnetic clusters have been performed using several calculation methods. These studies are expected to be available to realize high-density magnetic memories, new micro-magnetic devices or to analyze microscopically for magnetic non destructive evaluation. Monte Carlo (MC) method is one of useful and powerful methods to simulate magnetic process for magnetic clusters including complicated interaction such as different exchange interactions due to different elements and to introduce magnetic properties depending on temperature. To apply MC method for magnetic process simulation, there were some problems. One is that MC method is originally dealing with stable states, that is, the time processes on MC simulations can not be usually recognized as the real changes on time, e.g. for hysteresis curves (M-H curves) with increasing and decreasing applied magnetic field. Then a pseudodynamic process for MC method is introduced for dealing with such a simulation on section 2. Next problem is that the MC calculation for large clusters demands huge CPU time because it is necessary to repeat MC step (MCS) until N for the cluster cell number N. Especially the magnetic dipole interaction which is included in Hamiltonian must be calculated among all the spins in the cluster. Then a new technique of MC method by a parallelized program is introduced for dealing with larger cluster on section 3. The useful calculation results using these MC methods are presented on following sections. Section 4 introduces the producing of magnetic domains and domain walls (DWs) for the clusters including spins affected by exchange interaction, magnetic dipole interaction and crystal anisotropy. On section 5, magnetic domain wall displacements (DWDs) are shown for nanowires with local magnetic impurity. On section 6, M-H curves are shown for magnetic clusters with a local magnetic distribution corresponding with grain boundary of Ni based alloy. For elementary theory on MC method, previous chapter should be referred.