Effects of Pressure on the Electronic and Magnetic Properties of Bulk NiI$_{2}$

TL;DR

This study investigates how hydrostatic pressure influences the electronic and magnetic properties of bulk NiI$_{2}$, revealing pressure-induced enhancements in interlayer coupling and magnetic transition temperature through combined first-principles and experimental methods.

Contribution

It provides new insights into pressure effects on NiI$_{2}$'s magnetic interactions and structural parameters, expanding understanding of tunable 2D magnetic materials.

Findings

Interlayer antiferromagnetic coupling increases with pressure.

Magnetic transition temperature rises monotonically under pressure.

Pressure enhances magnetic frustration and modifies the helimagnetic ground state.

Abstract

Transition metal dihalides have recently garnered interest in the context of two-dimensional van der Waals magnets as their underlying geometrically frustrated triangular lattice leads to interesting competing exchange interactions. In particular, NiI$_{2}$ is a magnetic semiconductor that has been long known for its exotic helimagnetism in the bulk. Recent experiments have shown that the helimagnetic state survives down to the monolayer limit with a layer-dependent magnetic transition temperature that suggests a relevant role of the interlayer coupling. Here, we explore the effects of hydrostatic pressure as a means to enhance this interlayer exchange and ultimately tune the electronic and magnetic response of NiI$_{2}$. We study first the evolution of the structural parameters as a function of external pressure using first-principles calculations combined with x-ray diffraction measurements. We then examine the evolution of the electronic structure and magnetic exchange interactions via first-principles calculations and Monte Carlo simulations. We find that the leading interlayer coupling is an antiferromagnetic second-nearest neighbor interaction that increases monotonically with pressure. The ratio between isotropic third- and first-nearest neighbor intralayer exchanges, which controls the magnetic frustration and determines the magnetic propagation vector $\mathbf{q}$ of the helimagnetic ground state, is also enhanced by pressure. As a consequence, our Monte Carlo simulations show a monotonic increase in the magnetic transition temperature, indicating that pressure is an effective means to tune the magnetic response of NiI$_{2}$.