Abstract
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 Co${}_{x}$Fe${}_{3\ensuremath{-}x}$O${}_{4}$ ($x=0$, 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 \ensuremath{\sim}50$%$ in Fe${}_{3}$O${}_{4}$ (at 25 GPa) and by \ensuremath{\sim}70$%$ in Co${}_{1.5}$Fe${}_{1.5}$O${}_{4}$ (at 16 GPa) and Co${}_{2}$FeO${}_{4}$ (at 21 GPa). In CoFe${}_{2}$O${}_{4}$, the suppression by \ensuremath{\sim}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 CoFe${}_{2}$O${}_{4,}$ 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 CoFe${}_{2}$O${}_{4}$ is either paramagnetic or antiferromagnetic.
Highlights
In magnetic materials with strong electron correlations such as transition-metal oxides, lattice compression strongly affects transport, structural, and magnetic properties, often leading to a high-pressure-induced insulator-to-metal transition accompanied by the loss of its ferromagnetic long-range order and by a structural phase transition
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 synchrotron x-ray powder diffraction measurements indicate the occurrence of structural phase transitions at critical pressures in coincidence with the suppression of ferrimagnetism
Summary
In magnetic materials with strong electron correlations such as transition-metal oxides, lattice compression strongly affects transport, structural, and magnetic properties, often leading to a high-pressure-induced insulator-to-metal transition accompanied by the loss of its ferromagnetic long-range order and by a structural phase transition. Such transformations have been experimentally observed in various transition metal compounds, but the mechanisms of these transitions are still ambiguous in many respects especially in the relation to the local, atomic scale electronic and magnetic modifications at the high-pressure phase. Powder XRD experiments of this high-pressure structure were indexed in the orthorhombic unit cell (CaMn2O4-type structure, space group Pbcm) by Fei et al (Ref. 5) and in a more symmetric CaTi2O4-type structure (space group Bbmm), as proposed by Haavick et al (Ref. 6)
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