The magnetocaloric effect of exchange anisotropy

The magnetocaloric effect is a temperature change in magnetic materials when subjected to applied magnetic field variations. An inverse magnetocaloric effect occurs when applying a magnetic field adiabatically leads to sample cooling instead of heating. In the present study, we report on the inverse magnetocaloric effect in unidirectional ferromagnetic nanoparticles, demonstrating that this phenomenon can be controlled through interfacial exchange coupling at the nanoscale and within a moderate external field. The present results show that crystalline Ni80Fe20 nanoparticles diluted in an amorphous Al2O3 matrix exhibit the rich phenomena of coercive enhancement, hysteresis shifts, and training effects associated with the exchange anisotropy. The entropy changes are determined by this anisotropy.