Low-temperature magnetic ordering and structural distortions in vanadium sesquioxideV2O3

Abstract

Vanadium Sesquioxide (V2O3) is an antiferromagnetic insulator below TN ≈ 155 K. The magnetic order is not of C-or G-type as one would infer from the bipartite character of the hexagonal basal plane in the high-temperature corundum structure. In fact, the Néel transition is accompanied by a monoclinic distortion that makes one bond of the honeycomb plane inequivalent from the other two, thus justifying a magnetic structure with one ferromagnetic bond and two antiferromagnetic ones. We show here that the magnetic ordering, the accompanying monoclinic structural distortion, the magnetic anisotropy and also the recently discovered high-pressure monoclinic phase, can all be accurately described by conventional electronic structure calculations within GGA and GGA+U. Our results are in line with DMFT calculations for the paramagnetic phase 1 , which predict that the insulating character is driven by a correlation-enhanced crystal field splitting between e π g and a1g orbitals that pushes the latter above the chemical potential. We find that the a1g orbital, although almost empty in the insulating phase, is actually responsible for the unusual magnetic order as it leads to magnetic frustration whose effect is similar to a next-nearest-neighbor exchange in a Heisenberg model on a honeycomb lattice.

Frustrated Magnetism in Mott Insulating (V1−xCrx)2<

“…Indeed, we note that the only out-of-plane exchange constant J 5 = −1.2 (7) which is comparable in magnitude to J 6 does not substantially alter the pattern of magnetic excitations, and therefore does not appear to interfere with the frustration originating in the honeycomb basal plane. The importance of the next-nearest interaction J 6 within the honeycomb layers of pure V 2 O 3 was previously noted based on GGA+U calculations [23].…”

Ultrafast evolution and transient phases of a prototype out-of-equilibrium Mott–Hubbard material

“…2c,f, where we show the calculated density of states (DOS) from ref. 22. This inequivalent behaviour in temperature versus pressure of the MIT, and the related deep intertwining between strong correlations and lattice structure suggest that a major issue in time-resolved experiments is to distinguish a temperature increase from a transient non-thermal phase, such as hidden phases2728.…”

“…In spite of that, the a 1 g orbital remains mostly unoccupied in the PI phase, whereas the orbitals are occupied by almost one electron each2021. V 2 O 3 PI can thus be viewed as a half-filled two-band Mott insulator stabilized by the correlation-enhanced trigonal field that pushes above the Fermi energy ( E F ) the a 1 g orbitals2122, whose occupancy indeed jumps across the doping- or temperature-driven Mott transition23 causing the opening of a gap2425, while is smoother across the pressure-driven one1326. The nature and indicative energy position of the relevant orbitals for each phase can be found in Fig.…”

“…We considered a three-band Hubbard model at one-third filling for the t 2 g orbitals with the tight-binding hopping parameters of ref. 20, and analysed this model by means of the HF approximation22 using as control parameter, after a Legendre transform, the occupancy difference between and a 1 g orbitals. In order to describe an insulator within an independent particle scheme as HF we had to allow for magnetism; our insulator is thus closer to the antiferromagnetic insulator phase low-temperature phase rather than to the high-temperature PI22.…”

“…( c ) Orbital character of the DOS near E F extracted from ref. 22. ( d – f ) Same as ( a – c ) but for the PM phase.…”