Local symmetry breaking and orbital glass behaviour in CoFe2O4

Soumya Shephalika Behera; Isha; Arvind Kumar Yogi; V R Rao Medicherla; Parasmani Rajput; Archana Sagdeo; Jaspreet Singh; Vasant Sathe; R J Choudhary

arXiv · 2506.16857

Local symmetry breaking and orbital glass behaviour in CoFe2O4

Soumya Shephalika Behera·Isha·Arvind Kumar Yogi·V R Rao Medicherla·Parasmani Rajput·Archana Sagdeo·Jaspreet Singh·Vasant Sathe·R J Choudhary

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Abstract

The structural distortions, orbital correlations, and electronic states in cobalt ferrite (CoFe2O4) were investigated using complementary characterisation techniques, including SR-XRD, HAXPES, XANES, EXAFS, and Raman spectroscopy. SR-XRD confirms phase purity and 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 (JTD). The disappearance of this feature below 100 K signals orbital freezing and the onset of a glass-like orbital state. HAXPES measurements show multiplet splitting and charge-transfer satellite features in the Co and Fe 2p core levels, indicating mixed valence states and strong electron correlations. XANES analysis reveals hybridized p-d states and local coordination distortions. Temperature-dependent EXAFS measurements indicate increasing local disorder-particularly in Fe-O and Fe-Fe octahedral bonds as evidenced by enhanced Debye-Waller factors. These distortions, attributed to cation redistribution and oxygen vacancies, are static and asymmetric, primarily affecting the octahedral sublattice. Notably, signatures of cooperative Jahn-Teller distortions emerge in the intermediate temperature range (200-100 K) and disappear upon further cooling. Raman spectroscopy further supports these findings, revealing phonon anomalies and enhanced spin-phonon coupling in the same temperature range. Magnetic measurements indicate spin reorientation and exchange interaction anomalies that align with the orbital behaviour. Together, these results hint at a frustrated orbital state in CoFe2O4 possibly involving cooperative Jahn-Teller distortions, disrupted long-range coherence, and orbital glass behaviour offering new insights into the coupling of orbital, spin, and lattice degrees of freedom in spinel systems.

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Soumya Shephalika Behera, Isha, Arvind Kumar Yogi, V R Rao Medicherla, Parasmani Rajput, Archana Sagdeo, Jaspreet Singh, Vasant Sathe, R J Choudhary. 2025-06-20. Local symmetry breaking and orbital glass behaviour in CoFe2O4. https://arxiv.org/abs/2506.16857

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