Observation of thermal switching of a single ferromagnetic particle

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Abstract
A magnetic force microscope(MFM) has been shown to be able to detect fields emanating from submicrometer permalloy particles with magnetic moments as low as 10−13 emu. We have used this MFM equiped with an in situ electromagnet to study the angular dependence of the switching field H s (θ), and the probability of thermal switching of a single‐domain permalloy particle as a function of the time duration of an applied magnetic fieldH. The angular dependence of H s (θ) is significantly different from that expected for coherent rotation. For applied magnetic fields close to H s , the time dependence of the probability for not switching cannot be fit with a simple exponential. These data indicate that multiple‐energy barriers of similar height are involved in the thermally activated process responsible for the reversal.