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| Home > Publications database > Coupled charge, orbital, and spin degrees of freedom in geometricallyfrustrated YFe2O4 |
| Conference Presentation (Invited) | FZJ-2025-04085 |
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2025
Abstract: Rhombohedral rare earth ferrites RFe2O4 have a strong tendency for coupled charge (Fe2+/3+) andspin order, despite the strong geometrical frustration of the interactions [1]. For R=Lu or Yb correspondingsuperstructure reflections or diffuse scattering appear at ( 1313 ℓ). However, the size of Y3+is considerably larger, with calculations [2] suggesting smaller in-plane propagation such as ( 1414 ).Here, we focus on single-crystal x-ray diffraction performed on highly stoichiometric single crystals[3] of YFe2O4. Magnetization vs T indicates two subsequent highly hysteretic magnetic transitions,separating a low-temperature (LT), an intermediate (IT), and a high-temperature (paramagnetic, HT)phase. XRD shows that these transitions are structural as well. In the HT phase, diffuse scatteringat ( 1313 ℓ) is similar to other rare earth ferrites. However, cooling into the magnetic phases, sharpsuperstructure reflections at different positions appear, with propagation ( 272737 ) in IT and ( 141434 ) inLT. We refined the superstructure in both phases and applied bond-valence-sum (BVS) analysis toprobe the charge order [4].In the LT phase, the structure is refined in P-1, with the inversion center between the two Fe layers.The BVS indicates a full charge order, with two of the Fe sites having valence close to 2+ and theother two close to 3+. Although of ( 1414 )-type, the arrangement of the valences differs from the predictionin [2]. Structural distortions also suggest (ferro) orbital order of the Fe2+ sites.The IT phase is also refined in P1. A clear splitting of one Y indicates the presence of disorder,which is likely connected to a fragile nature of this phase, which was not theoretically predicted. Ofthe 7 Fe sites, BVS shows 3 to have valences very close to 2+, indicating a strong localization of 3electrons on these sites. However, the BVS of one of the sites is about 2.5, and for the remainingsites also further away from the ideal 3 (BVS~2.8). Thus the localization of electrons in the IT phaseis incomplete, and it must be a dynamic situation with electron hopping occurring.[1] M. Angst, Physica Status Solidi RRL, 7, 383 (2013).[2] M. Naka, A. Nagano, and S. Ishihara, Phys. Rev. B, 77, 224441 (2008).[3] Th. Mueller, J. de Groot, J. Strempfer, and M. Angst, J. Crystal Growth, 428, 40 (2015).[4] Th. Mueller and M. Angst, submitted to PRB.
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