Tunable polar distortions and magnetism in Gd$_x$La$_{1-x}$PtSb epitaxial films

TL;DR

This study investigates how lanthanide substitution in Gd$_x$La$_{1-x}$PtSb films affects their polar distortions, electronic structure, and magnetic properties, revealing tunable ferroelectricity, phase transitions, and magnetic behaviors.

Contribution

It demonstrates the controlled tuning of polar buckling, electronic phases, and magnetic interactions in Gd$_x$La$_{1-x}$PtSb films through isovalent substitution, a novel approach for engineering functional intermetallic materials.

Findings

Polar buckling increases with Gd content.

Phase transition from polar metal to semimetal at x=1.

Magnetic susceptibility peaks due to RKKY interactions.

Abstract

Hexagonal $ABC$ intermetallics are predicted to have tunable ferroelectric, topological, and magnetic properties as a function of the polar buckling of $BC$ atomic planes. We report the impact of isovalent lanthanide substitution on the buckling, structural phase transitions, and electronic and magnetic properties of Gd$_x$La$_{1-x}$PtSb films grown by molecular beam epitaxy (MBE) on c-plane sapphire substrates. The Gd$_x$La$_{1-x}$PtSb films form a solid solution from x = 0 to 1 and retain the polar hexagonal structure ($P6_3 mc$) out to $x \leq 0.95$. With increasing $x$, the PtSb buckling increases and the out of plane lattice constant $c$ decreases due to the lanthanide contraction. While hexagonal LaPtSb is a highly conductive polar metal, the carrier density decreases with $x$ until an abrupt phase transition to a zero band overlap semimetal is found for cubic GdPtSb at $x=1$. The magnetic susceptibility peaks at small but finite $x$, which we attribute to Ruderman Kittel Kasuya Yosida (RKKY) coupling between localized $4f$ moments, whose concentration increases with $x$, and free carriers that decrease with $x$. Samples with $x\geq 0.3$ show antiferromagnetic Curie-Weiss behavior and a Neel temperature that increases with $x$. The Gd$_x$La$_{1-x}$PtSb system provides opportunities to dramatically alter the polar buckling and concentration of local $4f$ moments, for tuning chiral spin textures and topological phases.