Uncovering the orbital order in MgV2O4

In spinel oxides, AB₂O₄, the B sites form geometrically frustrated pyrochlore lattices. This suppresses T_N and may give rise to exotic macroscopically degenerate classical spin liquid states [1]. Breaking of this degeneracy is typically due to longer-range couplings or lattice distortions.

In vanadium spinels, orbital degeneracy offers another route to degeneracy breaking. Theoretical studies have suggested that orbital order can lift the geometric frustration and two potential ground state orbital ordering (OO) schemes have been presented: real/complex orbital order (ROO/COO). Which of these OOs is consistent with the observed behavior has been the subject of debate [2-4].

This presentation will seek to resolve this question in MgV₂O₄. Previous studies were unable to reconcile the magnetic behavior with either ROO or COO [4]. I will present neutron scattering results which show signatures of the OO. Using generalized spin-wave theory the spectrum will be modeled and show how the OO lifts the frustration. This proposed OO will be shown to be consistent with the emergence of hysteresis in the diffuse scattering.

[1] Bai et al, PRL 122, 097201 (2019)

[2] Di Matteo, Jackeli and Perkins PRB 72, 020408(R) (2005)

[3] Perkins and Sikora PRB 76, 214434 (2007)

[4] Wheeler et al, PRB 82, 140406(R) (2010)