Field dependence of the magnetocaloric effect in materials with a second order phase transition:: A master curve for the magnetic entropy change

The field dependence of the magnetic entropy change can be expressed as Delta S-M proportional to H-n. For soft magnetic amorphous alloys n=1 well below the Curie temperature (T-C), n=2 in the paramagnetic range, and n approximate to 0.75 for T=T-C. The first value can be explained with simple arguments, n=2 is a consequence of the Curie-Weiss law, but n(T-C) deviates from mean field predictions. From the Arrott-Noakes equation of state, a relation between n(T-C) and the critical exponents has been obtained, showing remarkable agreement with experimental data (for an example alloy, predicted n=0.72 versus experimental n=0.73). A master curve behavior for the temperature dependence of Delta S-M measured for different maximum fields is proposed. (c) 2006 American Institute of Physics.