Electronic structure and magnetic properties of LaFeO3 at high pressure

The electronic ground state and magnetic properties of the wide-gapped antiferromagnetic insulator LaFeO3 have been investigated by Fe57 Mössbauer spectroscopy at pressures up to 63 GPa and temperatures of 7-300 K. Two separate magnetic-electronic phase transitions have been identified in the measured pressure range. At 300 K a new nonmagnetic phase begins to evolve at ∼30 GPa and coexists in ever increasing abundance with the original magnetic phase at pressures up to ∼45 GPa. In the range 45-55 GPa and 300 K the spectrum is comprised solely of a nonmagnetic phase having a single Fe site. Spectra recorded at 48 GPa and temperatures down to 7 K exhibit features of paramagnetic hyperfine structure. The results are consistent with a progressive transition from a magnetically ordered state to that of a spin-disordered state in the range 30-45 GPa. At 300 K and higher pressures of 55-63 GPa the nonmagnetic spectra show features of two sites with similar isomer shifts but different quadrupole splittings. Pressure evolution of the hyperfine interaction parameters and the magnetic transition at 30-45 GPa may be explained by a change of the original Fe high-spin state, namely, spin crossover to a low-spin configuration. The two sites at 55-63 GPa have been attributed to the coexistence of different charge states at crystallographically equivalent sites. These distinct charge states are supposed to represent both low-spin Fe(III) and Fe(II) as a result of fluctuations across a ligand-to-metal charge-transfer gap Δ∼kBT that has been reduced under high pressure.