LANDAU DESCRIPTION OF VOLUME INSTABILITIES IN ITINERANT MAGNETIC SYSTEMS

Long lasting discussions about the INVAR effect involve a two-spin-state model. Recent measurements [1] and band-structure calculations [2] seem to confirm low-spin and high-spin phases in Fe-INVAR alloys. We interpret the results of the band structure calculations in terms of an effective Ginzburg-Landau model. We obtain the temperature dependence of magnetization and thermal expansion by applying the functional integral method to this statistical model