Structure and magnetic properties of hausmannite a-Mn3O4, metastable high-pressure marokite ?-Mn3O4, and defected a-Mn3O4

The magnetic properties of tetragonal & alpha;-Mn3O4 spinel, its metastable high-pressure modification & gamma;-Mn3O4, and of an & alpha;-Mn3O4 modification with a high amount of lattice defects were investigated by direct current (dc) and alternating current (ac) magnetometry as well as by heat capacity measurements. An & alpha;-Mn3O4 phase modification with a high amount of lattice defects instead of the desired metastable high pressure & gamma;-Mn3O4 phase might unintentionally be obtained after the high-pressure application. The obtained results clarify strongly con-tradictory reports about the dc susceptibility data of & gamma;-Mn3O4 in the literature. Further, in situ low-temperature x-ray diffraction experiments from 150 to 275 K and Mn K-edge x-ray absorption spectroscopy experiments at 80 and 300 K do not indicate any structural transition to be coupled with the magnetic transition at 210 K for the given & gamma;-Mn3O4 sample. This is in contradiction with what was concluded from powder neutron diffraction alone in the literature, where a coupled structural transition accompanied with large atomic displacements of a Mn species was claimed to be accompanied to the magnetic transition.