Accessing new magnetic regimes by tuning the ligand spin-orbit coupling in van der Waals magnets

TL;DR

This study demonstrates that tuning the ligand spin-orbit coupling in van der Waals magnets like chromium trihalides can access new magnetic ground-states and regimes, revealing frustration and field-induced inter-layer coupling changes.

Contribution

It introduces a novel method of engineering magnetic ground-states in VdW materials by chemically tuning ligand SOC, supported by experimental and first-principles analysis.

Findings

Identification of a frustrated magnetic regime near CrCl₃.

Confirmation that ligand SOC competition drives magnetic frustration.

Observation of field-induced inter-layer coupling changes.

Abstract

Van der Waals (VdW) materials have opened new directions in the study of low dimensional magnetism. A largely unexplored arena is the intrinsic tuning of VdW magnets toward new ground-states. The chromium trihalides provided the first such example with a change of inter-layer magnetic coupling emerging upon exfoliation. Here, we take a different approach to engineer new ground-states, not by exfoliation, but by tuning the spin-orbit coupling (SOC) of the non-magnetic ligand atoms (Cl,Br,I). We synthesize a three-halide series, CrCl$_{3-x-y}$Br$_{x}$I$_{y}$, and map their magnetic properties as a function of Cl, Br, and I content. The resulting triangular phase diagrams unveil a frustrated regime near CrCl$_{3}$. First-principles calculations confirm that the frustration is driven by a competition between the chromium and halide SOCs. Furthermore, we reveal a field-induced change of inter-layer coupling in the bulk of CrCl$_{3-x-y}$Br$_{x}$I$_{y}$ crystals at the same field as in the exfoliation experiments.