Magnetic reversal time of a cobalt nanoparticle with defects*

Transition metal magnetic nanoparticles can exhibit a wide range of magnetic reversal times which cannot be explained by crystalline, shape and surface anisotropies. In this talk we consider how the presence of planar defects can affect the thermal switching properties of such Co particles. Specifically, we develop a formulation for the magnetic switching rate of a model defected Co nanoparticle based on the harmonic transition state theory which uses knowledge of the underlying magnetic energy landscape. We find that both the Arrhenius energy barrier and the prefactor depend on nanoparticle size and defect density. This result is able to rationalize the experimental findings.