Semiquantitative analysis of magnetic phase transitions in the MnFeP1-xAsx series of compounds

On the basis of the relation T(sigma, H) derived within the framework of the Bean-Rodbell model a semiquantitative analysis of (B, T) magnetic phase diagrams in the hexagonal region of the MnFeP1-xAsx (0.15 less than or equal to x less than or equal to 0.66) series of compounds was carried out. It was found that the first order transition line in the (B,T) plane is terminated by the isolated critical point for x = 0.33 and x = 0.5 contents, The positive value of dB(C)/dT and the saturation of the magnetization was found to be in agreement with the experiment. Thus the Bean-Rodbell model and the molecular field approximation can be applied to describe the discontinuous Ferro-Para magnetoelastic phase transition. Semiquantitative agreement between the theoretical and the experimental (B,T) magnetic phase diagrams was obtained. For the MnFeP0.67As0.33 compound the electronic structure calculations were performed by the Korringa-Kohn-Rostoker with the coherent potential approximation method. The density of states (DOS) curve calculated in the nonmagnetic state shows that the Fermi level falls in a deep minimum of DOS. It indicates that the metamagnetic B-field induced phase transition between the paramagnetic and the ferromagnetic states may be observed (metamagnetism of itinerant electrons) which remains in good agreement with our experimental results. (C) 1998 American Institute of Physics. [S0021-8979(98)52011-7].