Widely Tunable Berry Curvature in the Magnetic Semimetal Cr1+ δ Te2

Magnetic semimetals have increasingly emerged as lucrative platforms hosting spin-based topological phenomena in real and momentum spaces. Cr_{1+ δ} Te₂ is a self-intercalated magnetic transition metal dichalcogenide (TMD), which exhibits topological magnetism and tunable electron filling. While recent studies have explored real-space Berry curvature effects, similar considerations of momentum-space Berry curvature are lacking. Here, the electronic structure and transport properties of epitaxial Cr_{1+ δ} Te₂ thin films are systematically investigated over a range of doping, δ (0.33 - 0.71). Spectroscopic experiments reveal the presence of a characteristic semi-metallic band region, which shows a rigid like energy shift with δ. Transport experiments show that the intrinsic component of the anomalous Hall effect (AHE) is sizable and undergoes a sign flip across δ. Finally, density functional theory calculations establish a link between the doping evolution of the band structure and AHE: the AHE sign flip is shown to emerge from the sign change of the Berry curvature, as the semi-metallic band region crosses the Fermi energy. These findings underscore the increasing relevance of momentum-space Berry curvature in magnetic TMDs and provide a unique platform for intertwining topological physics in real and momentum spaces.

Slow Magnetic Relaxation and Luminescent Properties of Mononuclear Lanthanide-Substituted Keggin-Type Polyoxotungstates with Compartmental Organic Ligands

The reaction of mid to late lanthanide ions with the N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylene-diamine organic ligand and monolacunary Keggin type [α-SiW₁₁O₃₉]^8– anion affords a series of isostructural compounds, namely, K₅[Ln^III(α-SiW₁₁O₃₉)(C₂₀H₂₂Br₂N₂O₄)]·14H₂O (1-Ln, Ln = Sm to Lu). The molecular structure of these sandwich-type complexes is formed by the Ln^III ion in a biaugmented trigonal prismatic geometry, which occupies the external O₄ site of the organic ligand and the vacant site of the lacunary polyoxometalate (POM) unit. The empty N₂O₂ coordination site of the organic ligand allows its unprecedented folding, which displays a relative perpendicular arrangement of aromatic groups. Weak Br···Br and π–π interactions established between adjacent molecular units govern the crystal packing, which results in the formation of assemblies containing six hybrid species assembled in a chairlike conformation. 1-Gd and 1-Yb display slow relaxation of the magnetization after the application of an external magnetic field with maxima in the out-of-phase magnetic susceptibility plots below ∼5–6 K, which is ascribed to the presence of various relaxation mechanisms. Moreover, photoluminescent emission is sensitized for 1-Sm and 1-Eu in the visible region and 1-Er and 1-Yb in the NIR. In contrast, the quenching of metal-centered luminescence in the 1-Tb derivative has been attributed to the out-of-pocket coordination mode of the lanthanide center within the POM fragment. It is demonstrated that the 1-Yb dual magneto-luminescent material represents the first lanthanide-containing POM reported to date with simultaneous slow magnetic relaxation and NIR emission. Solution stability of the hybrid molecular species in water is also confirmed by ESI-mass spectrometry experiments carried out for 1-Tb and 1-Tm.

A series of solution stable, molecular polyoxometalate hybrids, namely, [α-SiW₁₁O₃₉Ln^III(C₂₀H₂₂N₂Br₂O₄)]⁵⁻ (Ln^III = Sm to Lu) have been synthesized from the combination of mid-to-late lanthanides, lacunary Keggin-type anions, and a compartmental organic ligand. Metal-centered luminescence in both the visible and NIR region as well as slow relaxation of magnetization was found for different members of this family, including the Yb derivative, which represents the first POM-based system with slow magnetic relaxation and sensitized emission in the NIR region.