Investigation of pressure-induced magnetic transitions in CoxFe3-xO4 spinels

Room temperature Fe and Co K-edge x-ray magnetic circular dichroism, synchrotron x-ray powder diffraction, and magnetization measurements were carried out to investigate the stability of the ferrimagnetic ground state in CoxFe3-xO4 (x = 0, 1, 1.5, and 2) ferrites under pressure up to about 30 GPa using diamond anvil cells. The x-ray magnetic circular dichroism at the Fe K-edge is observed to decrease continuously up to the highest reached pressure by similar to 50% in Fe3O4 (at 25 GPa) and by similar to 70% in Co1.5Fe1.5O4 (at 16 GPa) and Co2FeO4 (at 21 GPa). In CoFe2O4, the suppression by similar to 80% of the x-ray magnetic circular dichroic signal occurs simultaneously at both Fe and Co K-edges between 24 and 27 GPa. However, a continuous decrease of the dichroic signal with pressure is only observed at the Co K-edge, whereas the Fe K-edge dichroic intensity drops drastically. The synchrotron x-ray powder diffraction measurements indicate the occurrence of structural phase transitions at critical pressures in coincidence with the suppression of ferrimagnetism. In CoFe2O4, bulk magnetization measurements up to 26 GPa confirm the disappearance of ferrimagnetism and indicate an almost linear dependence of the magnetization with the magnetic field in the high pressure phase. We thus conclude that high-pressure CoFe2O4 is either paramagnetic or antiferromagnetic. DOI: 10.1103/PhysRevB.87.094408