Correction of the shape effect on magnetic entropy change in ball milled Fe70Zr30 alloys

Abstract

The field dependence of the magnetic entropy change (ΔS) after mechanical alloying of FeZr composition starting from high purity powders is studied. Samples with different shapes and different crystalline fraction X were analyzed. Although the results show that the proposed correction of the demagnetizing field has not a significant effect on ΔS(T) curves (∼5% underestimation), it is necessary in order to properly analyze the field dependence of this magnitude (|ΔS|=aH). This correction allows recovering the theoretically predicted field dependence as well as a deeper analysis on multiphase systems. In fact, the biphasic character of the studied system changes the value of the field exponent n: it decreases below two above Curie temperature (T), and it increases at T. We show that, assuming a non-interacting phase model, it is possible to obtain the value of the exponent n for the main phase from the intercept of n vs X/ΔS.