Exquisitely balanced thermal sensitivity of the stochastic switching process in macroscopic ferromagnetic ring elements

Abstract

We have studied the repeatability of the magnetic switching behavior of macroscopic ferromagnetic permalloy ring elements using focused magneto-optic Kerr effect magnetometry. In $5\mu \mathrm{m}$ diameter permalloy rings, the circulation of the stable vortex state is found to alternate stochastically from one applied field cycle to the next due to the influence of thermal fluctuations. Micromagnetic simulations are used to demonstrate that the symmetry of the structure creates an exquisitely balanced system where the configuration of a nanoscopic region of magnetic moments dictates the switching mechanism of the entire macroscopic structure, resulting in a degree of sensitivity to thermal agitation usually only observed in structures three orders of magnitude smaller.