ANOMALOUSLY HIGH ENTROPY CHANGE IN FERH ALLOY

The temperature dependences of heat expansion, elastocaloric effect, m agnetocaloric effect, and the shift in the critical temperature of the transition due to tensile stress have been measured using samples of the same concentration Fe49Rh51 in the antiferromagnetic-ferromagnetic (AF-F) transition range. Using data on specific heat and magnetocalor ic effects, entropy-temperature diagrams for the alloy were made for v arious magnetic fields. The ratios Delta S(T-cH)/T-cH, where Delta S(T -cH) is the entropy change during transition and T-cH is the transitio n's critical temperature, were found to be similar to 3.98x10(2) erg/g K-2 which is close to the value of the change in the electronic speci fic heat coefficient Delta gamma obtained by other researchers. It has been concluded that the change in the electronic part of entropy is t he main mechanism of the transition. The phenomenological model is pro posed, taking into account the electronic entropy change during the tr ansition. Calculations using the model give values for the main thermo dynamic parameters of the transition (free energy change Delta F = 1.9 1 X 10(6) erg/g, the critical temperature shift partial derivative T-c /partial derivative P = 3.08 X 10(-9) K cm(2)/Dyn and partial derivati ve T-c/partial derivative H = 0.788 K/kOe due to hydrostatic pressure and magnetic field respectively), which are in agreement with experime ntal data. (C) 1996 American Institute of Physics.