Magnetic collapse and the change of electronic structure of FeBO3 antiferromagnet under high pressure

Abstract

The effect of high pressures up to 60 GPa on single-crystal and polycrystalline samples of iron borate 57 FeBO 3 was studied by Mössbauer absorption spectroscopy ( 57 Fe nuclei) in a diamond anvil cell. Magnetic field H hf at the 57 Fe nuclei increases with pressure but abruptly drops to zero at 46±2 GPa, indicating the crystal transition from the antiferromagnetic to nonmagnetic state. This is accompanied by an abrupt change in the isomer shift and quadrupole splitting. Their values in the high-pressure phase are evidence for the transition of Fe +3 ions from a high-spin ( S =5/2, 6 A 1 g ) to low-spin ( S =1/2, 6 T 2 g ) state (spin crossover). This correlates with an abrupt decrease in the unit-cell volume (by ∼9%) and optical gap. The change of the magnetic and electronic structures is explained by Mott’s transition with rupturing of strong d - d -electron correlations.