Tunable polar distortions and magnetism in Gd_𝑥⁢La_1−𝑥⁢PtSb epitaxial films

Hexagonal 𝐴⁢𝐵⁢𝐶 intermetallics are predicted to have tunable ferroelectric, topological, and magnetic properties as a function of the polar buckling of 𝐵⁢𝐶 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 (𝑃⁢6₃⁢𝑚⁢𝑐) 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 4⁢𝑓 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 4⁢𝑓 moments.. Authors: Du, Dongxue [Univ. of Wisconsin, Madison, WI (United States)]; Zhang, Chenyu [Univ. of Wisconsin, Madison, WI (United States)] (ORCID:0000000274227027); Wei, Jingrui [Univ. of Wisconsin, Madison, WI (United States)]; Teng, Yujia [Rutgers Univ., New Brunswick, NJ (United States)] (ORCID:0009000200203441); Genser, Konrad T. [Rutgers Univ., New Brunswick, NJ (United States)]. DOE Contract: SC0023958. Subjects: 36 MATERIALS SCIENCE; electronic structure; ferroelectricity; magnetism; molecular beam epitaxy