Magnetization Switching in Nanoscale Ferromagnetic Grains: MFM Observables from Monte Carlo Simulations

H. L. Richards, S. W. Sides, M. A. Novotny, and P. A. Rikvold

In Physical Phenomena at High Magnetic Fields II, edited by Z. Fisk, L. Gor'kov, D. Meltzer, and R. Schrieffer (World Scientific, Singapore, 1996), pp. 386-391.

Abstract

Recently experimental techniques, such as magnetic force microscopy (MFM), have enabled the magnetic state of individual sub-micron particles to be resolved. Motivated by these experimental developments, we use Monte Carlo simulations of two-dimensional kinetic Ising ferromagnets to study the magnetic relaxation in a negative applied field of a grain with an initial magnetization m0 = +1. We use classical droplet theory to predict the functional forms for some quantities which can be observed by MFM. An example is the probability that the magnetization is positive, which is a function of time, field, grain size, and grain dimensionality. The qualitative agreement between experiments and our simulations of switching in individual single-domain ferromagnets indicates that the switching mechanism in such particles may involve local nucleation and subsequent growth of droplets of the stable phase.

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