Dynamical susceptibility of weakly interacting ferromagnetic nanoclusters.
The ac-susceptibility of weakly interacting ferromagnetic nanoclusters located at the vertices of a periodic lattice in a static applied field is calculated using a perturbation theory. The samples are nonspherical which gives rise to predominant shape effects due to dipolar interactions. The effects observed on the maximum of the two components of the dynamical susceptibility when increasing the strength of the dipolar interactions are opposite for prolate and oblate samples. It is also shown that a static applied field can invert these effects. The peak position of the out-of-phase component of the ac-susceptibility shifts towards lower temperatures with increasing the strength of the dipolar interactions in most cases in agreement with previous numerical studies on isotropic systems. It is shown that the opposite behaviour can be observed in the high damping case because of a sample shape effect.
Groupe de Physique des Matériaux, UMR 6634 CNRS, Université de Rouen, Avenue de I'université, BP 12, 76801 Saint-Etienne-du-Rouvray, France.
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D003198:Computer Simulation; D060526:Magnetic Fields; D059346:Magnets; D008956:Models, Chemical; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size