Quasi-chemical model of metamagnetism of intermetallic compounds

The theory of 'itinerant' metamagnetics is developed on the basis of the quasi-chemical model [5] of covalent bonds and their fluctuations (FCB) on the example of intermetallic compound (Fe1-yNiy)(Rh1-xPdx). Contributions to the thermodynamic potential (TDP) of band electrons' energies, FCB, 3d - 3d-exchange between Fe ions of different spin sublattices, indirect 3d - 4d - 3d exchange through covalent bonds of Fe and Rh ions (or Pd 5d ions) in ferromagnetic (FM) and antiferromagnetic (AFM) phases are calculated. 3d - 4d - 3d-exchange contribution to TDP depends strongly on temperature T. The compensation of difference of band contributions to TDP and 3d - 3d-exchange, which have opposite signs in FM and AFM phases, is the necessary condition of metamagnetic (MM) transition. The expression for temperature T = TMM of the centre of MM-transition range contains exchange parameters of various types, FCB correlations, electron band width t0 and Fermi energy ΕF. Width of MM-hysteresis range (or intermediate phase of MM-transition) is defined by exchange invariant of 4th order of smallness on spin polarization of covalent electrons. The possibility of b.c.c. - b.c.t. transition, observed in [6], is calculated on the model of FCB 'soft mode'.