Spin fluctuation driven structural phase transitions in itinerant electron magnets: γ→α transition in Ce-based compounds

We suggest a novel mechanism of structural transitions in itinerant electron magnets, driven by spin fluctuations strongly coupled to the crystal lattice. The mechanism explains the isostructural γ→α transition in Ce-based compounds. The high-temperature γ-phase is shown to be stabilized by spin fluctuations dominating the bulk modulus. With the decrease of temperature and spin fluctuation amplitudes the bulk modulus becomes negative giving rise to a structural instability. The structural phase transition to the low-temperature α-phase is accompanied by the change of the volume described in terms of the order parameter defined by the volume strain.