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 ΔSM∝Hn. For soft magnetic amorphous alloys n=1 well below the Curie temperature (TC), n=2 in the paramagnetic range, and n≈0.75 for T=TC. The first value can be explained with simple arguments, n=2 is a consequence of the Curie-Weiss law, but n(TC) deviates from mean field predictions. From the Arrott-Noakes equation of state, a relation between n(TC) 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 ΔSM measured for different maximum fields is proposed.