Heavy-Atom Antiferromagnet GdBiTe: An Interplay of Magnetism and Topology in a Symmetry-Protected Topological Semimetal

Magnetic topological semimetals (MTSs) are quantum materials highly desirable for spintronics. We report the synthesis, the crystal structure, the chemical bonding analysis, the magneto­(transport) properties, and the bulk and surface electronic structures of GdBiTe. It is a high-Z isostructural analogue of the archetypical nodal-line TS ZrSiS and a recently discovered MTS LnSbTe (Ln = Ce, Gd). GdBiTe crystallizes in the nonsymmorphic space group P4/nmm (No. 129) with a = 4.3706(2) Å and c = 9.2475(7) Å. Chemical bonding analysis describes it as a layered structure of alternating weakly bonded double-stacked covalent [GdTe] layers and planar square [Bi] nets. GdBiTe exhibits an antiferromagnetic transition at T_N = 15 K, and an additional transition, possibly a spin reorientation into a canted antiferromagnetic state, occurs below ca. 5 K. The electrical resistivity is compatible with a semimetallic behavior above T_N. The Hall coefficient is negative, reflecting an electron-like character of the transport in a semimetal. The magnetoresistance presents a negative contribution at temperatures lower than ca. 30 K, consistent with the freezing of spin fluctuations due to the applied field. First-principles calculations identify a collinear antiferromagnetic ground state with the Gd­(III) magnetic moments coupled ferromagnetically in-plane (easy axis along [100]) and antiferromagnetically along the c axis. This spin alignment differs from the reported LnSbTe and enables new scenarios of symmetry breaking due to magnetic order and spin–orbit coupling in a symmetry-protected topological semimetal. GdBiTe hosts exotic topological features resulting from an interplay of lattice symmetry, magnetism, and topology. Its collinear antiferromagnetic phase exhibits fingerprints of the nodal lines in the bulk electronic spectrum confined to k_z = π/c planes and a surface state with a symmetry-protected crossing at the (010) face, whereas the paramagnetic phase is a weak topological insulator and a higher-order topological insulator with topologically protected surface states at the (100), (010), and (001) planes. GdBiTe is also better suited for topological transport properties than LnSbTe thanks to a gapped trivial electron pocket at the Γ point. The isostructural LaBiTe was synthesized as a single-phase powder (sp. gr. P4/nmm; a = 4.48819(9) Å, and c = 9.5501(3) Å). Its bulk and surface electronic spectra are similar to the nonmagnetic case of GdBiTe.