Domain wall induced topological Hall effect in the chiral-lattice ferromagnet Fe$_x$TaS$_2$

TL;DR

The paper demonstrates that the topological Hall effect (THE) in Fe$_x$TaS$_2$ is domain-wall driven and highly tunable by Fe intercalation in a noncentrosymmetric lattice. By combining structural probes (SC-XRD, STEM/SAED), magnetic/transport measurements, and real-space imaging (MFM), the authors show that a pronounced THE emerges when striped, chiral domain walls are stabilized by Dzyaloshinskii–Moriya interaction in the $P6_3 22$ phase ($x \approx 0.30$), while it is absent in the centrosymmetric/less-ordered regime ($x \approx 0.26$). The work establishes Fe$_x$TaS$_2$ as a bulk platform where defect-driven control of domain-wall topology yields large electromagnetic responses, suggesting a pathway to low-power spintronic functionalities via domain-wall engineering in intercalated transition metal dichalcogenides. The findings underscore the importance of symmetry, disorder, and textured magnetism in designing topological transport in layered magnets.

Abstract

Magnetic topology and its associated emergent phenomena are central to realizing intriguing quantum states and spintronics functionalities. Designing spin textures to achieve strong and distinct electrical responses remains a significant challenge. Layered transition metal dichalcogenides offer a versatile platform for tailoring structural and magnetic properties, enabling access to a wide spectrum of topological magnetic states. Here, we report a domain-wall-driven, large, and tunable topological Hall effect (THE) in a non-centrosymmetric intercalated transition metal dichalcogenides series Fe$_x$TaS$_2$. By systematically varying the Fe intercalation level, we exert precise control over the magnetic ground states, allowing manipulation of the topological Hall effect. Real-space magnetic force microscopy (MFM) provides direct evidence of periodic magnetic stripe domain formation, confirming the microscopic origin of the observed topological transport phenomena. Our findings establish a promising way for tuning the topology of domains to generate substantial electromagnetic responses in layered magnetic materials.

Figures (24)

• Figure 1: a, Schematic of the crystal structure of Fe$_{1/3}$TaS$_2$. Green, red and yellow balls represent tantalum (Ta), iron (Fe) and sulfur (S) atoms, respectively. b, Precession image in the $(hki1)$ plane for $x \approx$ 0.30 recorded by single crystal X-ray diffraction. Strong reflections (yellow circles) are associated with the underlying 2H-TaS$_2$ structure, while weak reflections (white circles) correspond to the $\sqrt{3} \times \sqrt{3}$ ordered superlattice. c, Atomic resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image for $x \approx$ 0.30 along the [01$\bar{1}$0] zone axis. The inset shows the atomic arrangements. d, Selected area electron diffraction (SAED) pattern along the [001] for $x \approx$ 0.30. $\sqrt{3} \times \sqrt{3}$ superstructure unit cell is highlighted with a red hexagon, while the unit cell corresponding to TaS$_2$ is outlined by the green hexagon.
• Figure 2: a-c, Temperature-dependence of magnetic susceptibility [$\chi(T)$] measured with applied field of 0.1 T along the $c$-axis for Fe$_{x}$TaS$_2$ ( $x \approx$ 0.30, 0.28, 0.26). Insets show the temperature derivative of the magnetic susceptibility. d-f, Zero-field longitudinal resistivity $[\rho(T)]$ as a function of temperature with current applied along $ab$ ($I||ab$) for Fe$_x$TaS$_2$ ($x \approx$ 0.30, 0.28, 0.26).
• Figure 3: a-i, Field-dependent magnetization [$M(B)$] (black curve, plotted on the left axis) and Hall resistivity [$\rho_{H}(B)$] (red curve, plotted on the right axis) measured at selected temperatures for Fe$_{x}$TaS$_2$ with $x \approx 0.30$ (a-c), $x \approx 0.28$ (d-f), $x \approx 0.26$ (g-i). The applied field is along the c-axis ($B||c$) and the current is along the $ab$ plane ($I||ab$). The dip-like topological features are highlighted by black circles. The directions of the magnetic field sweeps are indicated by arrows.
• Figure 4: a-h, Field evolution of magnetic domains for $x \approx 0.30$ at 15 K. i, In-situ Hall resistivity measured simultaneously for $x \approx 0.30$ at 15 K. The THE features are outlined by the black circles in the Hall resistivity. The color bar represents the change in resonance frequency of the cantilever’s oscillation due to magnetic interactions between the MFM tip and the sample. The black arrows indicate the direction of the magnetic field sweeps.
• Figure 5: a-e, Field evolution of magnetic domains at 7.8 K for $\approx 0.26$. f, Simultaneously measured in-situ Hall resistivity at 7.8 K on the same sample. The black arrows indicate the direction of the magnetic field sweeps.