MAGNETOCALORIC EFFECT OF FERROMAGNETIC PARTICLES

The entropy change accompanying the removal of an applied magnetic fie ld (i.e., the magnetocaloric effect) has been calculated for a system of magnetic spins independent of each other and also clustered togethe r into independently-acting magnetic particles. Mean-field-theory calc ulations have also been made for interacting, single magnetic spins an d also for interacting, magnetic particles. In both cases, there are f ound temperature and field regimes where the entropy changes are large r when the spins are coupled together into nanometer-sized magnetic pa rticles. Entropy change data is shown for a new Gd3Ga5-xFexO12 (x less -than-or-equal-to 2.5) magnetic nanocomposite confirming the calculati ons and possessing magnetocaloric effects larger than the presently pr eferred low temperature paramagnetic refrigerant, gadolinium gallium g arnet.