Monte Carlo study of the transverse susceptibility in ordered arrays of magnetic nanoparticles

Abstract

We present Monte Carlo simulations of the reversible transverse susceptibility (RTS) for a hexagonal array of dipolar interacting magnetic nanoparticles with random anisotropy. RTS curves with the bias field in-plane and out-of-plane are compared. With increasing temperature the RTS curves evolve from a three-peak $({H}_{C},\ifmmode\pm\else\textpm\fi{}{H}_{K})$ structure to a double-peak and eventually a single-peak at the blocking temperature of the system. This trend is preserved for weak interactions. Dipolar interactions at low temperature are responsible for the suppression of the ${H}_{C}$ peak in the out-of-plane geometry and its progressive merge to the ${H}_{K}$ peak with decreasing interparticle separation in the in-plane geometry. The ${H}_{K}$ peaks are located at higher field values in the out-of-plane geometry relative to the in-plane one. When the bias field lies in-plane (out-of-plane) the ${H}_{K}$ peaks are shown to shift to lower (higher) field values with decreasing interparticle separation. The ${H}_{C}$ peak shifts to lower field values in both geometries. Our results are compared with recent experimental findings in self-assembled arrays of Fe nanoparticles.