One-dimensional orbital fluctuations and the exotic magnetic properties of YVO${}_3$

Abstract

Starting from the Mott insulator picture for cubic vanadates, we derive and investigate the model of superexchange interactions between V${}^{3+}$ ions, with nearly degenerate $t_{2g}$ orbitals occupied by two electrons each. The superexchange interactions are strongly frustrated and demonstrate a strong interrelation between possible types of magnetic and orbital order. We elucidate the prominent role played by fluctuations of $yz$ and $xz$ orbitals which generate ferromagnetic superexchange interactions even in the absence of Hund's exchange. In this limit we find orbital valence bond state which is replaced either by $C$-type antiferromagnetic order with weak $G$-type orbital order at increasing Hund's exchange, or instead by $G$-type antiferromagnetic order when the lattice distortions stabilize $C$-type orbital order. Both phases are observed in YVO${}_3$ and we argue that a dimerized $C$-type antiferromagnetic phase with stronger and weaker FM bonds alternating along the c axis may be stabilized by large spin-orbital entropy at finite temperature. This suggests a scenario which explains the origin of the exotic $C$-AF order observed in YVO${}_3$ in the regime of intermediate temperatures and allows one to specify the necessary ingredients of a more complete future theory.

arXiv comment23 pages, 15 figures

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• Probing orbital fluctuations in RVO3 (R = Y, Gd, or Ce) by ellipsometry
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• Defect-induced orbital polarization and collapse of orbital order in doped vanadium perovskites
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• Spin--orbital physics in transition metal oxides
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• Imprinted atomic displacements drive spin-orbital order in a vanadate perovskite
• A Colossal Electroresistance response, accompanied by metal-insulator transition, in a mixed-valent vanadate
• Low-energy V t2g orbital excitations in NdVO3
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• Tuning Crystal Field Potential by Orbital Dilution in $d^4$ Oxides