Intrinsic Magnetism of Grain Boundaries in Two-dimensional Metal Dichalcogenides

TL;DR

This study reveals that grain boundaries in 2D metal dichalcogenides can induce magnetic properties, turning these materials into potential 2D magnetic semiconductors through structural engineering.

Contribution

It demonstrates that dislocations and grain boundaries in MX2 materials can generate and control magnetism, a novel property not observed in similar 2D materials.

Findings

Dislocations exhibit magnetic moments of ~1 Bohr magneton.

Grain boundaries transition from semiconductor to half-metal or metal with tilt angle/doping.

Square-octagon pairs induce antiferromagnetic semiconducting behavior.

Abstract

Grain boundaries (GBs) are structural imperfections that typically degrade the performance of materials. Here we show that dislocations and GBs in two-dimensional (2D) metal dichalcogenides MX2 (M = Mo, W; X = S, Se) can actually improve the material by giving it a qualitatively new physical property: magnetism. The dislocations studied all have a substantial magnetic moment of ~1 Bohr magneton. In contrast, dislocations in other well-studied 2D materials are typically non-magnetic. GBs composed of pentagon-heptagon pairs interact ferromagnetically and transition from semiconductor to half-metal or metal as a function of tilt angle and/or doping level. When the tilt angle exceeds 47{\deg} the structural energetics favor square-octagon pairs and the GB becomes an antiferromagnetic semiconductor. These exceptional magnetic properties arise from an interplay of dislocation-induced localized states, doping, and locally unbalanced stoichiometry. Purposeful engineering of topological GBs may be able to convert MX2 into a promising 2D magnetic semiconductor.