Eu2Mg3Bi4: Competing Magnetic Orders on a Buckled Honeycomb Lattice

The honeycomb lattice and its derived variants provide information on modeling and designing quantum magnets. A novel magnetic material, Eu2Mg3Bi4, which stabilizes in a previously unknown buckled honeycomb lattice, was discovered by high-pressure and high-temperature methods. We report here on the synthesis exploration of pure single crystals, structural determination of the buckled honeycomb lattice of europium moments, and experimental observation of competing magnetic phases in metallic Eu2Mg3Bi4. The crystal structure of Eu2Mg3Bi4 is orthorhombic and centrosymmetric with the space group Cmce and Eu atoms in a buckled honeycomb lattice. The dominant antiferromagnetic interaction associated with magnetic coupling within the buckled honeycomb layers is confirmed based on the high Curie–Weiss fitting with TCW ∼ −24 K. However, the long-range magnetism orders are in a temperature range far below TCW. Two transitions observed at TN1 = 4.0 K and TN2 = 6.0 K likely originate from the competing magnetic interactions in Eu2Mg3Bi4. Two sharp anomalies that occur in the magnetic susceptibility, zero-field resistivity, and heat capacity all suggest successive evolution of magnetic order parameters, which is frequently observed in magnets with competing interactions. This magnetism and structure entanglement provides an ideal platform to study the interplay between honeycomb lattice rare-earths and quantum magnets, thus realizing the design and control of magnetism from the structural aspects.