Thermomagnetic analysis of FeCoCr_xNi alloys: Magnetic entropy of high-entropy alloys

摘要

The equimolar alloy FeCoCrNi, a high-entropy alloy, forms in the face-centered-cubic crystal structure and has a ferromagnetic Curie temperature of 130 K. In this study, we explore the effects of Cr concentration, cold-rolling, and subsequent heat treatments on the magnetic properties of FeCoCr_xNi alloys. Cr reductions result in an increase of the Curie temperature, and may be used to tune the T_C over a very large temperature range. The magnetic entropy change for a change in applied field of 2T is ΔS_m = -0.35 J/(kg K) for cold-rolled FeCoCrNi. Cold-rolling results in a broadening of ΔS_m, where subsequent heat treatment at 1073 K sharpens the magnetic entropy curve. In all of the alloys, we find that upon heating (after cold-rolling) there is a re-entrant magnetic moment near 730 K. This feature is much less pronounced in the as-cast samples (without cold-rolling) and in the Cr-rich samples, and is no longer observed after annealing at 1073 K. Possible origins of this behavior are discussed.