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Spin resolved electron density study of YTiO₃ in its ferromagnetic phase: signature of orbital ordering.

ABSTRACT: The present work reports on the charge and spin density modelling of YTiO₃ in its ferromagnetic state (T _C = 27?K). Accurate polarized neutron diffraction and high-resolution X-ray diffraction (XRD) experiments were carried out on a single crystal at the ORPHÉE reactor (LLB) and SPRING8 synchrotron source. The experimental data are modelled by the spin resolved pseudo-atomic multipolar model (Deutsch et al., 2012 ?). The refinement strategy is discussed and the result of this electron density modelling is compared with that from XRD measured at 100?K and with density functional theory calculations. The results show that the spin and charge densities around the Ti atom have lobes directed away from the O atoms, confirming the filling of the t _2g orbitals of the Ti atom. The d _xy orbital is less populated than d _xz and d _yz , which is a sign of a partial lift of degeneracy of the t _2g orbitals. This study confirms the orbital ordering at low temperature (20?K), which is already present in the paramagnetic state above the ferromagnetic transition (100?K).

SUBMITTER: Voufack AB

PROVIDER: S-EPMC6760435 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Spin resolved electron density study of YTiO3 in its ferromagnetic phase: signature of orbital ordering.

Voufack Ariste Bolivard AB Kibalin Iurii I Yan Zeyin Z Claiser Nicolas N Gueddida Saber S Gillon Béatrice B Porcher Florence F Gukasov Arsen A Sugimoto Kunishisa K Lecomte Claude C Dahaoui Slimane S Gillet Jean-Michel JM Souhassou Mohamed M

IUCrJ 20190802 Pt 5

The present work reports on the charge and spin density modelling of YTiO3 in its ferromagnetic state (T C = 27 K). Accurate polarized neutron diffraction and high-resolution X-ray diffraction (XRD) experiments were carried out on a single crystal at the ORPHÉE reactor (LLB) and SPRING8 synchrotron source. The experimental data are modelled by the spin resolved pseudo-atomic multipolar model (Deutsch et al., 2012 ▸). The refinement strategy is discussed and th ...[more]

PMID: 31576221

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Project description:We describe the electronic structure and the origin of ferromagnetic exchange coupling in two new metal complexes, NN-SQ-Co(III)(py)(2)Cat-NN (1) and NN-Ph-SQ-Co(III)(py)(2)Cat-Ph-NN (2) (NN = nitronylnitroxide radical, Ph = 1,4-phenylene, SQ = S = (1)/(2) semiquinone radical, Cat = S = 0 catecholate, and py = pyridine). Near-IR electronic absorption spectroscopy for 1 and 2 reveals a low-energy optical band that has been assigned as a Psi(u) --> Psi(g) transition involving bonding and antibonding linear combinations of delocalized dioxolene (SQ/Cat) valence frontier molecular orbitals. The ferromagnetic exchange interaction in 1 is so strong that only the high-spin quartet state (S(T) = (3)/(2)) is thermally populated at temperatures up to 300 K. The temperature-dependent magnetic susceptibility data for 2 reveals that an excited state spin doublet (S(T) = (1)/(2)) is populated at higher temperatures, indicating that the phenylene spacer modulates the magnitude of the magnetic exchange. The valence delocalization within the dioxolene dyad of 2 results in ferromagnetic alignment of two localized NN radicals separated by over 22 A. The ferromagnetic exchange in 1 and 2 results from a spin-dependent delocalization (double exchange type) process and the origin of this strong electron correlation has been understood in terms of a valence bond configuration interaction (VBCI) model. We show that ferromagnetic coupling promoted by organic mixed-valency provides keen insight into the ability of single molecules to communicate spin information over nanoscale distances. Furthermore, the strong interaction between the itinerant dioxolene electron and localized NN electron spins impacts our ability to understand the exchange interaction between delocalized electrons and pinned magnetic impurities in technologically important dilute magnetic semiconductor materials. The long correlation length (22 A) of the itinerant electron that mediates this coupling indicates that high-spin pi-delocalized organic molecules could find applications as nanoscale spin-polarized electron injectors and molecular wires.

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Spin resolved electron density study of YTiO₃ in its ferromagnetic phase: signature of orbital ordering.

Publications

Spin resolved electron density study of YTiO<sub>3</sub> in its ferromagnetic phase: signature of orbital ordering.

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