Abstract and subjects
A long-range magnetic ordering transition in cobalt oxide (CoO) was observed around 2.2 GPa at room temperature using neutron diffraction. The magnetic structure was type-II antiferromagnetic. High-resolution synchrotron x-ray diffraction showed no evidence of a tetragonal lattice distortion in CoO in the magnetically ordered phase. This result indicates that the tetragonal lattice distortion occurring with magnetic ordering in the low-temperature structure of CoO could be associated with cooperative Jahn-Teller effects (orbital ordering), which, however, are decoupled from magnetic ordering under high pressure.