ИСТИНА

The nearly equiatomic Fe-Rh alloys undergo first-order phase transition from antiferromagnetic (AFM) to ferromagnetic (FM) state upon heating, during which phase volume increases by about 1 % but the bcc crystal structure of the compound is preserved. This phase transition in Fe-Rh is accompanied by a giant magnetocaloric effect (MCE) which reaches its maximum value at the AFM - FM transition temperature [1]. Understanding the nature of the first-order magnetic phase transition in FeRh and the character of the co-existing phases may help to discover other compounds with comparable or even stronger MCEs. Further, FeRh-based alloys are promising for applications in medicine and heat-assisted memory recording (HAMR) technologies. Here we present the results of detailed investigation of magnetization and MCE in an annealed Fe49Rh51 sample. Special attention has been paid to the process of preparation and characterization of the sample. The adiabatic temperature change ?T has been obtained during direct dynamic MCE measurements with the field change rate varying between 1 T/s and 5 T/s. The isothermal magnetic entropy change ?SM has been calculated from magnetization data measured in the temperature range 250 K - 370 K and magnetic fields up to 2 T. Results show that the phase transition temperature is decreased when the magnetic field is increased with rate -13.2 K/T (from 340 K at magnetic field of 0.1 T to 315 K at magnetic field of 2 T). We demonstrate that the ?SM reaches 8.9 Jkg-1K-1 (4.45 Jkg-1K-1/T) and the peak has the width of 18 K at the half-maximum of the ?SM(T) curve in magnetic field of 2 T. Our data indicate a stronger and narrower peak when compared with data published earlier for an annealed sample [1], which can be related to a sharper AFM-FM transition.