The electronic ground state and magnetic properties of the wide-gapped antiferromagnetic insulator ${\mathrm{LaFeO}}_3$ have been investigated by ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ 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∼${\mathit{k}}_{\mathit{B}}$T that has been reduced under high pressure.

• Received 20 December 1994

DOI:https://doi.org/10.1103/PhysRevB.51.11495