Anisotropic anomalous Hall effect in distorted kagome GdTi3Bi4

Topological kagome magnets offer a rich landscape for exploring the intricate interplay of quantum interactions among geometry, topology, spin, and correlation. GdTi3Bi4 crystallizes in layered Ti based kagome nets intertwined with zigzag Gd chains along the a axis and orders antiferromagnetically below 15 K. Here, we present the temperature and field dependent electrical transport of GdTi3Bi4 in different directions. The material exhibits anomalous Hall conductivity (AHC) of 410 S cm-1 at 2 K for B parallel c and it is completely absent for B parallel a, despite the similar magnetization observed in both orientations. This behavior is quite contradictory, as anomalous Hall effect (AHE) typically scales with the magnetization. Through first principles calculations, it is demonstrated that in the presence of time reversal symmetry broken by the Gd 4f sublattice and spin orbit coupling, the magnetization direction controls the orbital mixing in the Ti t2g bands, relocating Berry curvature hot spots and producing the observed orientation selective AHC. The results establish GdTi3Bi4 as platform for investigating new avenues of AHE, such as directional AHE, and thus shed new light on the intricate coupling between magnetic and electronic structures, paving the way for exploring novel quantum phenomena.

💡 Research Summary

The authors investigate the anisotropic anomalous Hall effect (AHE) in the kagome‑derived compound GdTi₃Bi₄, a layered material that combines a slightly distorted Ti‑based kagome net with zig‑zag Gd chains running along the crystallographic a‑axis. Single crystals grown by a Bi self‑flux method crystallize in the orthorhombic space group Fmmm (a = 5.858 Å, b = 10.299 Å, c = 24.726 Å). Magnetization measurements reveal an antiferromagnetic transition near 15 K and a series of metamagnetic transitions, including a 1/3 magnetization plateau, for magnetic fields applied both parallel to the c‑axis and the a‑axis. Despite nearly identical magnetization curves for the two field orientations, transport measurements show a striking dichotomy: with B ∥ c the Hall resistivity contains a large anomalous component, yielding an anomalous Hall conductivity (σ_AHE) of about 410 Ω⁻¹ cm⁻¹ at 2 K, whereas for B ∥ a the Hall response is purely ordinary and σ_AHE is essentially zero.

To uncover the origin of this directional AHE, the authors perform fully relativistic density‑functional calculations that include a Hubbard U on the Gd 4f states and spin‑orbit coupling (SOC). The Gd 4f moments break time‑reversal symmetry and generate an exchange field that polarizes the Ti t₂g manifold. Crucially, the direction of the magnetization controls the mixing of Ti d orbitals (primarily d_xy, d_xz, and d_yz). For B ∥ c the SOC‑induced anticrossings near the Fermi level become strongly mixed, creating concentrated Berry‑curvature “hot spots” in momentum space. These hot spots produce a sizable intrinsic contribution to the AHE, consistent with the experimentally observed σ_AHE. When the field is rotated to B ∥ a, the same anticrossings are either lifted or their orbital character changes such that the Berry curvature is largely quenched, explaining the disappearance of the anomalous Hall signal despite comparable magnetization.

A scaling analysis of the anomalous Hall resistivity (ρ_AHE) versus the longitudinal resistivity (ρ_xx) shows a dominant ρ_AHE ∝ ρ_xx² behavior, indicating that intrinsic Berry‑curvature and side‑jump mechanisms dominate over skew‑scattering. Linear fits of ρ_AHE/ρ_xx versus ρ_xx between 4 K and 14 K give an intrinsic σ_AHE of ~360 Ω⁻¹ cm⁻¹, in good agreement with the measured value. The deviation from linearity at 2 K suggests a subtle reconstruction of the electronic structure, possibly linked to a transition from a 3Q to a 2Q charge‑density‑wave order reported in earlier work.

Angle‑dependent Hall measurements further confirm that only the component of the magnetic field perpendicular to the current contributes to the Hall voltage, reinforcing the notion that the anomalous response is tied to the perpendicular magnetization component. A logarithmic plot of σ_AHE versus σ_xx places GdTi₃Bi₄ in the intrinsic regime (10⁴ – 10⁶ Ω⁻¹ cm⁻¹), where the AHE is largely independent of scattering.

In summary, GdTi₃Bi₄ exemplifies a “directional anomalous Hall effect” where the orientation of the magnetic field, rather than its magnitude or the net magnetization, dictates the presence of a large intrinsic Hall response. The study demonstrates that in kagome‑based systems with intertwined magnetic chains and distorted lattices, the magnetization direction can act as a switch for Berry‑curvature distribution, opening avenues for designing direction‑controlled topological transport devices and deepening our understanding of magnetism‑topology interplay in correlated electron materials.