Impact of Planar Defects on the Reversal Time of Single Magnetic Domain Nanoparticles.

Recent experimental investigations of individual magnetic nanoparticles reveal a diverse range of magnetic relaxation times which cannot be explained by considering their size, shape, and surface anisotropy, suggesting other factors associated with the internal microstructure of the particles are at play. In this Letter, we apply Langer's theory of thermal activation to fcc Co nanoparticles exhibiting single domain magnetism, whose experimentally observed microstructure contain planar defects. Our analytical derivation yields an expression for the activation rate as a function of the particle size and the defect fraction, enabling a quantitative understanding of the experimental findings. These dependencies, which are exponential for both the Arrhenius exponential and its prefactor, demonstrate the critical role that structural defects can play in the magnetic stability of nanoparticles.