Tunable polar distortions and magnetism in Gd 𝑥 La 1−𝑥 PtSb epitaxial films
Hexagonal 𝐴𝐵𝐶 intermetallics are predicted to have tunable ferroelectric, topological, and magnetic properties as a function of the polar buckling of 𝐵𝐶 atomic planes. Here, 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 𝑥=1 and retain the polar hexagonal structure (𝑃6 3 𝑚𝑐) out to 𝑥 ≤ 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≥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.