Monte carlo simulations of magnetizations with various lattice defects

Abstract

Aiming at nondestructive evaluation of magnetic materials, Monte Carlo simulations of the dynamic magnetic processes were investigated on the temporal and the temperature dependences for spin systems with various lattice imperfections as so called Barkhausen noises. From physical point of view, the presented method might be the more useful tool for the analyses of the dynamic magnetic processes rather than those by Preisach model. We have been investigated on the Nondestructive Evaluations (NDE) of iron-based structural materials by detecting the magnetic property changes with increasing fatigues. Therefore, the observations of magnetic properties have been expected as diagnosis method for NDE. For these purposes of NDE, many researchers have been studied on the magnetic properties of structural materials (1-9). Figure 1 shows an example of experimentally observed Barkhausen Noises (BN) spectra at sample position as function of applied field up to 14 mT with different yoke angles against the sample elongation direction for an iron-based material (A533B) with residual stress caused by tensile stress of 600 MPa. The alphabets in this figure indicated by a-l stand for the different yoke angle directions against the sample elongating direction. The spectrum of g was observed with magnetic yoke pair (N-S) configuration in the perpendicular direction against the long sample. Here, the spectra of a and l stand for the observations in the parallel direction with the sample. As it is apparently seen, the BN spectra show large dependences on the observed yoke directions. Further, experimental results vary with the complicated combinations of the observing positions, angles, sample shape, preparations, annealing conditions, sample history, ambient temperatures and the chemical compositions. The microscopic processes and the method of the analyses for BN, therefore, have not been sufficiently studied due to this complexity. The difficulty of BN analysis seems to be cause by the dynamic process including localized magnetic potentials and by the transient de-pinning processes. By these reasons, the itinerant model could not be adopted for these analyses. The Preisach model is neither applicable because the total M-H curves are composed of many miner loops describing the steady states even though dM/dH at each point could be defined. In this paper, we developed special Monte-Carlo (MC) method with