A critical discussion of calculated modulated structures, Fermi surface nesting and phonon softening in magnetic shape memory alloys Ni2Mn(Ga, Ge, Al) and Co2Mn(Ga, Ge)

A series of first-principle calculations have been carried out in order to discuss electronic structure, phonon dynamics, structural instabilities and the nature of martensitic transformations of the Heusler alloys Ni2Mn(Ga, Ge, Al) and Co2Mn(Ga, Ge). The calculations show that besides electronic peculiarities like Fermi-surface nesting, hybridizing optical and acoustic phonon modes are important for the stabilization of the modulated martensitic structures.