Magnetic-Field Switching of Crystal Structure in an Orbital-Spin-Coupled System:MnV2O4

Abstract

Strong spin-orbit coupling (SOC) can result in ground states with non-trivial topological properties. The situation is even richer in magnetic systems where the magnetic ordering can potentially have strong influence over the electronic band structure. The class of AMnBi2 (A = Sr, Ca) compounds are important in this context as they are known to host massive Dirac fermions with strongly anisotropic dispersion, which is believed to be due to the interplay between strong SOC and magnetic degrees of freedom. We report the optical conductivity of YbMnBi2, a newly discovered member of this family and a proposed Weyl semi-metal (WSM) candidate with broken time reversal symmetry. Together with density functional theory (DFT) band structure calculations, we show that the complex conductivity can be interpreted as the sum of an intra-band Drude response and inter-band transitions. We argue that the canting of the magnetic moments that has been proposed to be essential for the realization of the WSM in an otherwise antiferromagnetically ordered system is not necessary to explain the optical conductivity. We believe our data is explained qualitatively by the uncanted magnetic structure with a small offset of the chemical potential from strict stochiometry. We find no definitive evidence of a bulk Weyl nodes. Instead we see signatures of a gapped Dirac dispersion, common in other members of AMnBi2 family or compounds with similar 2D network of Bi atoms. We speculate that the evidence for a WSM seen in ARPES arises through a surface magnetic phase. Such an assumption reconciles all known experimental data. INTRODUCTION Correlated electron systems with strong SOC have been the subject of intensive research in recent years. The interplay of electronic correlations and SOC can result in emergent topological phases and has opened up a completely new direction in condensed matter physics. This interplay can be very different depending on the specifics of the electronic correlation. In weakly to moderately interacting electron systems, SOC can lead to non-trivial band topology as observed in conventional topological insulators [1], Dirac and Weyl semi-metals [2-4], axion insulators [5] and topological superconductors [6]. More recently, the effects of SOC on strongly correlated systems are being explored with the realization of new material systems with heavy 4d/5d transition metal compounds [7]. The iridates deserve special mention in this category and have been instrumental in exploring much of this uncharted territory [8, 9]. In addition to the emergence of topologically non-trivial ground states, the interplay between SOC and magnetic degrees of freedom themselves is also quite interesting. The family of AMnBi 2 (A = Sr, Ca) compounds are particularly important in this context. Being structurally similar to iron based superconductors, they are referred to as manganese pnictides, which contain layers of Mn-Bi edge sharing tetrahedra and a Bi square net separated by a layer of A atoms [10]. These compounds were expected from firs...

Effects of inter-vanadium distance andA-site magnetism inAV2O4(AKiswandhi1, Ma2, Brooks3 et al. 2014Phys. Rev. B15190View full textAdd to dashboardCite

“…In our case, the substitution with Co 2+ decreases both the effective moment of the A-site and the anisotropy of the system due to the completely filled e orbital, so T S decreases and the phase separation disappears. This reduction in T S is also observed in other study on substitution of Mn 2+ for a non-magnetic A 2+ cation 21,22 .…”

“…A study by Adachi et al, demonstrates the magnetic field dependence of T S in MnV 2 O 4 where T S increases with increasing field 21 . This indicates a strong correlation between magnetic field and T S where the field stabilizes the tetragonal structure, which in turn also signifies the role of the magnetic A 2+ cation in spinels.…”

Towards the theory of ferrimagnetism

“…Another example is the manganese vanadium oxide spinel M nV 2 O 4 [16]. On one of the sublattices sites is M n +2 in a 3d 5 high spin configuration s = 5/2 with quenched orbital angular momentum.…”

Ferrimagnetism of MnV2O4spinel

“…This Letter is inspired from the experimental measurements of the ZFC magnetization of M nV 2 O 4 [1,2,3]. The profile of the experimental curve reproduces the anomalous magnetization curve predicted by L. Neel [4,5] for ferrimagnets with equal sublattice spins.…”