Nonmonotonic evolution of the blocking temperature in dispersions of superparamagnetic

D. SERANTES; D. BALDOMIR; M. PEREIRO; C. E. HOPPE; F. RIVADULLA; J. RIVAS

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 2010 vol. 82 p. 1344331 - 1344336

1098-0121

We use a Monte Carlo approach to simulate the influence of the dipolar interaction on assemblies of monodisperse superparamagnetic _-Fe2O3 nanoparticles. We have identified a critical concentration c_, that marks the transition between two different regimes in the evolution of the blocking temperature _TB_ with interparticle interactions. At low concentrations _c_c__, magnetic particles behave as an ideal noninteracting system with a constant TB. At concentrations c_c_, the dipolar energy enhances the anisotropic energy barrier and TB increases with increasing c so that a larger temperature is required to reach the superparamagnetic state. The fitting of our results with classical particle models and experiments supports the existence of two differentiatedregimes. Our data could help to understand apparently contradictory results from the literature