Role of magnetic interparticle coupling on the field dependence of the superparamagnetic relaxation time

Abstract

Magnetic properties of Co-SiO 2 granular films are displayed and explained by means of a phenomenological model that takes into account the effects of magnetic interparticle coupling on the superparamagnetic relaxation behavior. The model is based on the analysis of coupled nanoparticles through a modified random anisotropy model that takes into account the concentration and size of the nanoscopic particles, as well as the field dependence of the correlation length. The proposed model leads to an accurate description of the field dependence of the blocking temperature, substantially better than the power law usually employed to describe noninteracting particles.

Using Monte Carlo Method to Study Magnetic Properties of Frozen Ferrofluid

“…This phenomenal approach obtained several good agreements with experiments of granular solids (Nunes et al, 2005;Knobel et al, 2008). However, it has not still given a general view on collective states of strongly interacting magnetic nanoparticle systems (Knoble et al, 2008).…”

“…Now, we will briefly consider a recent approach which was developed by Nunes et al (Nunes et al 2005). This approach was based on the random anisotropy model (RAM) which was developed to describe the magnetic properties of amorphous magnetic materials.…”

“…By substituting the effective anisotropy and effective volume of each particle in expression (6) on the expression (5), the authors obtained the expression for the blocking temperature of couple particles in the term of structural parameter (Nunes et al, 2005) as follow ( …”

“…The aim of this approach is to calculate the blocking temperature under the influence of the interactions in the presence of external field. Therefore, the authors began from the expression (5) with the two relevant parameters which need to be modified, namely effective anisotropy and effective volume V eff of particles in the correlation length L (Nunes et al, 2005) eff…”

Size effects in the magnetic behaviour of TbAl2milled alloys

“…A qualitative picture of the magnetic structure of mechanically milled ) of the ZFC maxima which is associated to glassy magnetic behaviour [34]. Recent reports on ferromagnetic nanograins with a large degree of interparticle (dipolar) interactions, suggest that the variation should follow a H 1/2 [39]; however, this is not the case in the TbAl 2 nanoparticle samples. On the other hand, the χ ac (T) presents a dynamic behaviour in which, although the general shape is not far from that of bulk-TbAl 2 , the analysis of the T f (ν) gives a low value for the relative shift per frequency decade of 0.0026(3) and can be fitted with the Vogel-Fulcher phenomenological law with T 0 = 41 K for the interaction temperature and E a /k B = 64 K for the activation energy in the 300 hours-TbAl 2 .…”