Magnetic Ordering and Bonding in Ln3TiBi5 (Ln = Pr, Nd, Gd)

Abstract Topological materials have gained remarkable attention due to their exotic properties and potential applications in advanced devices. The Ln3MPn5 (Ln = lanthanide, M = transition metal, Pn = pnictide) family, which hosts hypervalent Bi chains, has been identified as a promising platform to study magnetic topological materials. Herein, we present single-crystal growth of new compounds Ln3TiBi5 (Ln = Pr, Nd, and Gd) and their property characterization. Magnetic measurements on Pr3TiBi5 show no apparent indications of magnetic ordering down to 2 K, whereas both Nd3TiBi5 and Gd3TiBi5 show antiferromagnetic ordering at 6.2 and ∼18 K, respectively. Gd3TiBi5 exhibits antiferromagnetic transitions at 17.1 K (H ∥ c) and 18.8 K (H ⊥ c), respectively, suggesting competing ground states of this compound. Heat capacity measurements on the samples confirm the presence of magnetic ordering. DFT calculations reveal band crossings that are located above the Fermi level in Pr3TiBi5 and Nd3TiBi5, while the band structure of Gd3TiBi5 exhibits topologically nontrivial states near the Fermi level. In the presence of SOC, the electronic structure of Gd3TiBi5 changes dramatically. In particular, a local gap opens at the band crossing along M–K, and the band crossing along Γ–A moves above the Fermi level. The crystal orbital Hamilton population (COHP) calculations illustrate the bonding character of Ln-Bi6g, Ln-Bi4d, Ti–Bi6g, Bi4d-Bi4d, and Ti–Ti in Ln3TiBi5 (Ln = Pr, Nd, Gd). Ln forms the strongest bonds with Bi6g, followed by Ti–Bi6g and Ln-Bi4d. Bi4d–Bi4d in 1D Bi2– chains forms hypervalent bonding, with both bonding and antibonding states below the Fermi level. Ti–Ti interactions are relatively weak compared with the other bonding interactions. This work fills the gap in the Ln3TiBi5 family with the synthesis of Pr3TiBi5 and Nd3TiBi5 and also extends it to Gd3TiBi5, the first Gd-containing compound in the anti-Hf5Sn3Cu-type series.