Modeling of a twisted-Kagome HoAgGe spin ice using Reduced-Configuration-Space Search and Density Functional Theory

TL;DR

This paper combines first-principles calculations, reduced-configuration-space search, and Monte Carlo simulations to model the complex magnetic behavior of twisted-Kagome HoAgGe spin ice, revealing more accurate exchange parameters and phase diagram predictions.

Contribution

It introduces a novel combination of computational methods to accurately determine model parameters and phase behavior in twisted-Kagome spin ice materials.

Findings

First-principles exchange parameters differ significantly from empirical ones.

The new parameters better reproduce the experimental phase diagram.

The study highlights the importance of parametric frustration in modeling.

Abstract

The Kagome lattice is a 2D network of corner sharing triangles found in several rare earth materials resulting in a complicated and often frustrated magnetic system. In the last decades, modifications of the motif, such as breathing Kagome, asymmetric Kagome, and twisted Kagome were brought into the limelight. In particular, the latter has lower symmetry than the original Kagome and thus allows implementations of an "Ising-local" Hamiltonian, leading to a 2D spin ice. One such material implementation, HoAgGe, was recently reported to have an exceptionally rich phase diagram and is a strongly frustrated 2D spin-ice material with a twisted-Kagome geometry. In the presence of an external magnetic field the compound exhibits step-like magnetization plateaus at simple fractions of the saturation magnetization. It is believed that this phenomenon results from strong single-site anisotropy, which in HoAgGe was found to be in-plane and along a high-symmetry direction. Previous Monte Carlo simulations with empirical exchange parameters explain some, but not all experimental observations. In this work we present (a) first-principle calculations of the crucial model parameters and (b) direct energy minimization via a Reduced-Configuration-Space search, as well as Monte-Carlo simulations of the field-dependent phase diagram. We find that for HoAgGe the calculated exchange parameters are very different from the earlier suggested empirical ones, and describe the phase diagram much more accurately. This is likely because the first-principles parameters are, in addition to geometrically, also parametrically frustrated.