ITINERANT ANTIFERROMAGNETISM IN FEGE2

FeGe2, and lightly doped compounds based on it, have a Fermi surface d riven instability which drive them into an incommensurate spin density wave state. Studies of the temperature and magnetic field dependence of the resistivity have been used to determine the magnetic phase diag ram of the pure material which displays an incommensurate phase at hig h temperatures and a commensurate structure below 263 K in zero field. Application of a magnetic field in the tetragonal basal plane decreas es the range of temperatures over which the incommensurate phase is st able. We have used inelastic neutron scattering to measure the spin dy namics of FeGe2. Despite the relatively isotropic transport the magnet ic dynamics is quasi-one-dimensional in nature. Measurements carried o ut on HET at ISIS have been used to map out the spin wave dispersion a long the c-axis up the 400 meV, more than an order of magnitude higher than the zone boundary magnon for wave vectors in the basal plane.