The main results of the study of the temperature dependence of the macroscopic anisotropy in nanoparticles within the Néel surface anisotropy model, with different lattices and shapes are summarized as follows:
- By means of the constrained Monte Carlo method, we have been able to evaluate the temperature dependence of macroscopic anisotropies in nanoparticles with different shapes and internal structures. An additional cubic anisotropy, due to the spin non-collinearities produced by the surface anisotropy was detected in chapter 2 at
. This effect persists when the temperature is included.
- The additional cubic anisotropy shows a faster dependence of temperature that the uniaxial core anisotropy. Therefore, the temperature-induced re-orientation transition from the cubic anisotropy to the bulk one can be observed. This effect is similar to the reorientation transition in thin films. It has a pure surface origin and it is independent from the structural changes which may occur in nanoparticles with temperature.
- The scaling exponent of the anisotropy with magnetization depends on the surface anisotropy value and is always lower than the bulk scaling exponent due to strong magnetization fluctuations at the surface.
Rocio Yanes
