Transition from ferromagnetism to superparamagnetism in uniaxial nanoparticles. the role on non-uniformities in the magnetization

摘要

Langevin dynamics is used to study the transition from ferromagnetic to superparamagnetic behavior upon reducing the panicle size in uniaxial nanoparticles for observation times of a few nanoseconds and constant temperature T= 300 K. Square panicles of size d, thickness t= 1 nm and damping constant λ = O.1 are considered. The stochastic dynamic equation, interpreted in the Stratonovich sense [1], is solved on a two-dimensional grid of 1 nm square cells using a first-order Euler scheme augmented by the noise-induced drift term [1]. The transition is studied in detail by monitoring the probability distribution of in-plane magnetization orientations during the time interval considered.