SYNCHROTRON-EXCITED RESONANT MOSSBAUER STUDY OF MAGNETIC PROPERTIES UNDER PRESSURE UP TO 80GPa. Saburo Nasu, Department of Material Physics, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan

Using a diamond anvil cell, 57Fe Mossbauer spectroscopy under pressure up to 80GPa has been performed with the nuclear forward scattering of synchrotron radiation. A pressure-induced hyperfine interaction at 57Fe in SrFeO₃ has been detected at 44GPa and 300K for a first time by a quantum-beat modulation of the decay rate after collective nuclear excitation by the synchrotron pulse. Linearly polarized synchrotron pulse can easily make to clarify the direction of the hyperfine magnetic fields at nucleus. Nuclear forward scattering experiments of SrFeO₃ at 74GPa under external magnetic field suggest the existence of the pressure-induced magnetic phase transition from antiferro- to ferromagnetic in SrFeO₃.