Giant orbital magnetization in two-dimensional materials

TL;DR

This paper investigates the unquenched orbital magnetization in 2D materials, demonstrating how specific crystal field conditions and advanced calculations predict large orbital moments with significant implications for magnetic properties.

Contribution

It identifies 174 2D monolayers with potential for large orbital magnetization and emphasizes the importance of Hubbard corrections and self-consistent spin-orbit coupling in accurate predictions.

Findings

112 monolayers with octahedral crystal field splitting identified

62 monolayers with tetrahedral crystal field splitting identified

Hubbard corrections and spin-orbit coupling increase orbital moments by an order of magnitude

Abstract

Orbital magnetization typically plays a minor role in compounds where the magnetic properties are governed by transition metal elements. However, in some cases, the orbital magnetization may be fully unquenched, which can have dramatic consequences for magnetic anisotropy and various magnetic response properties. In the present work, we start by summarizing how unquenched orbital moments arise from particular combinations of crystal field splitting and orbital filling. We exemplify this for the cases of two-dimensional (2D) VI$_3$ and FePS$_3$, and show that Hubbard corrections as well as self-consistent spin-orbit coupling are crucial ingredients for predicting correct orbital moments from first principles calculations. We then search the Computational 2D Materials Database (C2DB) for monolayers having tetrahedral or octahedral crystal field splitting of transition metal $d$-states and orbital occupancy that is expected to lead to large orbital moments. We identify 112 monolayers with octahedral crystal field splitting and 62 monolayers with tetrahedral crystal field splitting and for materials with partially filled $t_{2g}$ bands, we verify that inclusion of Hubbard corrections as well as self-consistent spin-orbit coupling typically increases the magnitude of predicted orbital moments by an order of magnitude.