Local symmetry breaking and orbital glass like behaviour in CoFe₂O₄

In the present manuscript, structural distortions, orbital correlations, and electronic states in cobalt ferrite (CoFe2O4) were investigated using several synchrotron-based techniques, including temperature-dependent X-ray diffraction, hard X-ray photoelectron spectroscopy, and temperature-dependent extended X-ray absorption fine structure measurements, along with Raman spectroscopy and magnetisation measurements. Synchrotron X-ray diffraction confirms the phase purity of CoFe2O4and reveals a temperature-dependent superlattice reflection between 200 K and 100 K, consistent with the emergence of short-range orbital ordering driven by cooperative Jahn-Teller distortion. The disappearance of this feature below 100 K suggests the freezing of short-range orbital correlations into an orbital-glass-like regime. Raman spectroscopy further supports these observations through phonon anomalies and enhanced spin-phonon coupling in the same temperature range where the superlattice reflection appears. Hard X-ray photoelectron spectroscopy measurements reveal multiple spectral features along with charge-transfer satellites in the Co and Fe core levels, indicating mixed valence states and strong electron correlations. Temperature-dependent extended X-ray absorption fine structure measurements indicate increasing local disorder, particularly in the Fe-O and Fe-Fe octahedral bonds, as evidenced by enhanced Debye-Waller factors. These static and symmetric distortions, attributed to cation redistribution and oxygen vacancies, predominantly affect the octahedral sublattice. Magnetisation measurements reveal spin reorientation and exchange interaction anomalies that correlate with the observed orbital behavior. Altogether, these results point toward a frustrated orbital regime in CoFe2O4, possibly involving cooperative Jahn-Teller distortions and the freezing of short-range orbital correlations without the development of long-range orbital order.