Thermally activated transformation of magnetization-reversal modes in ultrathin nanoparticles

The influence of thermal fluctuations on magnetization-reversal processes i n ultrathin magnetic particles is investigated on the basis of a numerical solution of the Landau-Lifshitz-Gilbert equations taking account the therma l-activation fluctuation field. It is shown that for nanoparticles there ex ists a region of magnetic and geometric parameters where a strong jump-like instability of the critical field for magnetization reversal arises. This instability is due to the thermally activated transformation of magnetizati on configurations far from the switching threshold. The thermal-instability mechanism described is important for particles of much larger sizes than f or the single-mode Neel-Brown instability. (C) 1999 American Institute of P hysics. [S0021-3640(99)00608-8].