Magnetism and origin of non-monotonous concentration dependence of the bulk modulus in Fe-rich alloys with Si, Ge and Sn: a first-principles study

Using the first-principles calculations based on the coherent potential approximation, we study the electronic structure, magnetic moments and the bulk modulus of FeX alloys with IVB group elements ( X = Si, Ge, Sn) in the Fe-rich concentration range (x = 0.0 - 0.25), which form a stability region of bcc-related phases. In agreement with experiment, our calculations reproduce well a peculiar non-monotonous behaviour of the bulk modulus in Fe - Si alloys with increasing Si concentration. Such a dependence is found for all bcc-related disordered and partially ordered Fe - Si phases A2, B2 and D0(3), which is in contrast with an earlier suggestion that the non-monotonous bulk modulus behaviour is related to partial ordering in Fe - Si. In addition, our results predict a similar behaviour in Fe - Ge and Fe - Sn alloys. It is shown that the observed behaviour of the bulk modulus is entirely related to the changes of the magnetic properties with chemical composition.