Effect of very high pressure on the magnetic state of transition metal compounds

By simultaneously combining the methods of X-ray diffraction for structural phase transitions and EOS measurements, Fe-57 Mossbauer spectroscopy as a site-sensitive probe, and resistivity measurements for studying insulating-metal transitions, we are able to study the effect of extreme pressures and at varying temperature on magnetic and electronic properties of transition metal compounds. Studies are carried out with specially tailored diamond anvils and diamond anvil cells, reaching pressures beyond 100 GPa. From our studies, we can investigate the most basic phenomenon of the quantum effect of magnetism in insulating anti ferromagnets, the Mott insulators, such as high to low spin crossovers, quenching of the magnetic moments' orbital term, and the collapse of the Mott-Hubbard state. Examples of these phenomena will be given in cases of ferrous and ferric oxides, ferrous-halides and the rare-earth iron perovskites.