Magnetocaloric effect in dipolar chains of magnetic nanoparticles with collinear anisotropy axes

We study the magnetocaloric effect (MCE) in parallel one-dimensional chains of dipole-dipole interacting magnetic nanoparticles with collinear magnetic anisotropy axes. By means of a Monte Carlo method we simulate the magnetic field dependence of the MCE for a field applied perpendicular to the anisotropy axes, finding the coexistence of direct and inverse MCE being both of reversible character. The inverse MCE-temperature range is quite small and progressively shifts to lower temperatures with increasing applied field until it disappears, thus we have mainly focused our study on the direct MCE-temperature range. We show the existence of a particular magnetic field value being proportional to the anisotropy field of the particles, H^≈2.5HA, which optimizes the magnetic entropy change and refrigerant capacity of the collinear aligned ensemble of nanoparticles.