Field dependence of the adiabatic temperature change in second order phase transition materials: Application to Gd

The field dependence of the adiabatic temperature change Delta T-ad of second order phase transition materials is studied, both theoretically and experimentally. Using scaling laws, it is demonstrated that, at the Curie temperature, the field dependence of Delta T-ad is characterized by H-1/Delta. Therefore, as the magnetic entropy change Delta S-M follows a H(1-alpha)/Delta power law, these two dependencies coincide only in the case of a mean field model. A phenomenological construction of a universal curve for Delta T-ad is presented, and its theoretical justification is also given. This universal curve can be used to predict the response of materials in different conditions not available in the laboratory (extrapolations in field or temperature), for enhancing the resolution of the data and as a simple screening procedure for the characterization of materials. (C) 2009 American Institute of Physics. [doi:10.1063/1.3261843]