Single crystal growths and magnetic properties of hexagonal polar semimetals RAuGe (R = Y, Gd-Tm, and Lu)

TL;DR

This study investigates the structural and magnetic properties of RAuGe semimetals, revealing systematic structural evolution and magnetic anisotropy changes, with implications for electron-spin interactions in noncentrosymmetric polar materials.

Contribution

It provides the first detailed analysis of the structural crossover and magnetic anisotropy evolution in RAuGe semimetals, supported by experimental and theoretical CEF modeling.

Findings

Confirmed structural evolution with ionic radius.

Identified anisotropy change from easy-plane to Ising-type.

Estimated Ising gap energy (~11 meV) in TmAuGe.

Abstract

We study structural and magnetic properties of rare-earth based semimetals RAuGe (R = Y, Gd-Tm, and Lu) using flux-grown single crystals. These compounds belong to the noncentrosymmetric polar space group P63mc. We confirm the systematic structural evolution at room temperature as a function of ionic radius of rare earths to clarify the isopointal crossover between two polar structures: three-dimensional LiGaGe-type and quasi-two-dimensional NdPtSb-type. Magnetism shows a characteristic anisotropy in reasonable agreement with the crystal electric field (CEF) theory; the easy-plane-type anisotropy for R = Tb and Dy turns into the Ising-type anisotropy for R = Er and Tm. We evaluate the CEF parameters based on the Stevens operators to reasonably reproduce the temperature dependence of magnetic susceptibilities and specific heat for RAuGe (R = Tb-Tm). The estimated energy scale of the Ising gap (~ 11 meV) in TmAuGe is consistent with an excitation observed in an inelastic neutron scattering experiment. These findings suggest an opportunity for interplay between conduction electrons and nontrivial spin structures in the family of magnetic polar semimetals RAuGe.