🔬 mesoscale physics

Topological Hall Effect Induced by Chiral Spin Textures at the Ferroelectric/Ferromagnetic Interface

This study demonstrates that switching the ferroelectric polarization in few-layer Fe $_3$ GeTe $_2$ / $\alpha$ -In $_2$ Se $_3$ heterostructures nonvolatily modulates interfacial Dzyaloshinskii-Moriya interaction-stabilized chiral spin textures, enabling the generation of four distinct Hall resistance states for advanced spintronic applications.

Original authors: Jingkuan Xiao, Yaqing Han, Jianfeng Guo, Renjun Du, Jiawei Jiang, Baoshan Cui, Runnong Zhou, Siqin Wang, Siqi Jiang, Fuzhuo Lian, Di Zhang, Guodong Ma, Jiabei Huang, Zhaochen Qu, Wanting Xu, Kenji Wat

Published 2026-09-30

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Jingkuan Xiao, Yaqing Han, Jianfeng Guo, Renjun Du, Jiawei Jiang, Baoshan Cui, Runnong Zhou, Siqin Wang, Siqi Jiang, Fuzhuo Lian, Di Zhang, Guodong Ma, Jiabei Huang, Zhaochen Qu, Wanting Xu, Kenji Watanabe, Takashi Taniguchi, Alexander S. Mayorov, Jinsheng Wen, Haifeng Ding, Gong Chen, Ahmet Avsar, Hongxin Yang, Lihong Bao, Hong-Jun Gao, Shiyu Zhu, Lei Wang, Geliang Yu

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a world where the tiny magnetic switches inside your computer could be flipped not just by electricity, but by a simple change in the material's internal electric state, allowing for memory that is faster, smaller, and uses far less power. This is the promise of spintronics, a field that seeks to harness the spin of electrons—their intrinsic magnetic orientation—rather than just their charge. For decades, scientists have been hunting for ways to create and control exotic magnetic patterns, known as chiral spin textures, which act like tiny, stable whirlpools of magnetism. These patterns are special because they are topologically protected, meaning they are robust against disturbances, making them ideal candidates for the next generation of data storage. However, creating these patterns in a way that can be easily turned on and off by an electric signal has remained a significant challenge, particularly in the ultra-thin, two-dimensional materials that are the building blocks of future electronics.

A team of researchers has now taken a major step forward by demonstrating a new way to generate and control these magnetic whirlpools at the interface between two different types of ultra-thin crystals. They built a device by stacking a magnetic material called iron-germanium-telluride on top of a ferroelectric material known as indium-selenium. Ferroelectric materials are unique because they possess a permanent electric polarization that can be flipped back and forth by applying a voltage, much like a switch that remembers its last position even after the power is turned off. By bringing this "electric switch" into direct contact with the magnetic layer, the researchers created a system where the electric state of one layer could directly influence the magnetic behavior of the other.

When the team applied a magnetic field to this stacked device, they observed a surprising phenomenon in the electrical current flowing through it. Instead of a smooth, predictable change in resistance, the current exhibited two distinct, hump-shaped signals that appeared on opposite sides of the point where the magnetism flipped direction. These signals are known as the topological Hall effect, a tell-tale sign that electrons are moving through a landscape of twisting magnetic textures. The researchers found that these signals were not random noise but were directly linked to the formation of tiny magnetic bubbles within the material. Using a powerful microscope that can "see" magnetic fields, they watched these bubbles appear and disappear as the magnetic field was adjusted. They discovered that one type of bubble, with a specific magnetic orientation, formed at lower field strengths, while a second type, with the opposite orientation, emerged at higher field strengths. Each type of bubble produced a distinct topological Hall signal, explaining the two separate humps observed in the electrical data.

The study revealed that these magnetic textures are not a bulk property of the entire material but are stabilized specifically at the interface where the two crystals meet. As the researchers added more layers to the magnetic crystal, the signals became weaker and disappeared at lower temperatures, confirming that the effect relies on the unique conditions created right at the boundary. This interface breaks a fundamental symmetry in the crystal structure, which generates a specific interaction that forces the magnetic spins to twist into these stable, chiral patterns. The researchers used computer simulations to model the behavior of individual atoms and confirmed that the twisting is driven by this interfacial force, which competes with the material's natural tendency to align in a uniform direction.

Perhaps the most significant finding is that these magnetic patterns can be controlled using a combination of electric voltage and magnetic fields. Because the bottom layer is ferroelectric, the researchers could flip its internal electric polarization by applying a voltage pulse. This change in electric state altered the electronic environment at the interface, which in turn modulated both the standard magnetic resistance and the topological Hall signals. By combining the ability to switch the magnetic direction with the ability to switch the electric polarization, the team demonstrated that they could create four distinct, stable states in a single device. Each state corresponds to a unique combination of magnetic and electric settings, effectively turning the device into a non-volatile memory cell that can store two bits of information instead of the usual one.

This work provides a clear path toward creating electronic devices that are not only more efficient but also capable of storing more information in a smaller space. The ability to write and read data using both electric and magnetic fields is a crucial step toward low-power computing. While the current experiments were conducted at very low temperatures, the principles demonstrated here suggest that similar effects could be engineered in other materials to work at room temperature. The researchers have shown that by carefully designing the interface between two simple, two-dimensional materials, it is possible to create complex, controllable magnetic behaviors that were previously difficult to achieve. This discovery opens the door to a new class of electronic components where the flow of information is governed by the intricate dance of magnetic textures, all controlled by the application of voltage and magnetic pulses.

Technical Summary: Topological Hall Effect Induced by Chiral Spin Textures at the Ferroelectric/Ferromagnetic Interface

Problem Statement
Chiral spin textures, such as skyrmions and magnetic bubbles, stabilized by the Dzyaloshinskii-Moriya interaction (DMI), are promising candidates for next-generation spintronic devices due to their topological stability and non-volatile nature. While two-dimensional (2D) van der Waals (vdW) heterostructures offer a platform for engineering interfacial DMI through broken inversion symmetry and spin-orbit coupling, a comprehensive understanding of the microscopic mechanisms governing the formation and stabilization of these textures remains challenging. Furthermore, achieving active, reversible, and non-volatile electrical control over the Topological Hall Effect (THE) in these systems is a significant hurdle. Existing studies have identified THE signatures in various ferromagnet-based systems, but direct real-space observation of chiral textures in air-sensitive few-layer devices and the demonstration of non-volatile electrical tuning of both the Anomalous Hall Effect (AHE) and THE have been limited.

Methodology
The study employs a multi-faceted approach combining experimental characterization, theoretical modeling, and first-principles calculations on a dual-gated van der Waals heterostructure composed of the itinerant ferromagnet Fe $_3$ GeTe $_2$ (FGT) and the room-temperature ferroelectric $\alpha$ -In $_2$ Se $_3$ (IS).

Device Fabrication: Dual-gated devices were constructed using few-layer FGT (3L, 4L, and 5L) and IS layers, leveraging their small lattice mismatch (~0.8%).
Transport Measurements: Magnetotransport measurements were conducted to isolate the Hall resistance ( $R_H$ ). The authors utilized antisymmetrization to remove longitudinal contributions and subtracted the ordinary Hall background. The AHE background was further refined using Remanent Magneto-Circular Dichroism (RMCD) measurements to extract the pure THE signal.
Imaging: Low-temperature Magnetic Force Microscopy (MFM) was performed to visualize real-space spin textures and correlate them with transport data.
Simulations and Calculations: Atomistic spin-dynamics simulations were conducted using parameters derived from first-principles calculations (VASP) to model magnetic reversal and topological charge evolution. First-principles calculations were also used to analyze interfacial charge redistribution, electron doping levels, and anomalous Hall conductivity under different ferroelectric polarization states.

Key Contributions and Results

Identification of Dual Topological Hall Signals: The study identifies two distinct groups of topological Hall signals (THE1 and THE2) emerging on opposite sides of the coercive field in FGT/IS heterostructures. These signals are attributed to interfacial chiral spin textures stabilized by interfacial DMI, rather than intrinsic multi-channel effects or magnetic inhomogeneities.
Thickness-Dependent Suppression: Transport measurements reveal a strong dependence on FGT thickness. The critical temperature for THE1 drops from ~80 K in 3L devices to below 20 K in 4L and 5L devices. First-principles calculations indicate that as FGT thickness increases, the interfacial DMI strength ( $|D_N|$ ) decreases while the exchange interaction ( $J_N$ ) increases, shifting the system toward bulk-like ferromagnetism and reducing the stability window for chiral textures.
Real-Space Correlation: MFM imaging at 4 K and 15 K reveals two types of magnetic bubbles with opposite magnetic contrasts (red and blue) appearing at different magnetic fields near the coercive point. A direct correlation is established between the density of these bubbles and the magnitude of the corresponding THE signals (THE1 and THE2), providing direct evidence that the dual THE arises from the field-driven reversal of core-background polarity in the spin textures.
Non-Volatile Ferroelectric Control: The ferroelectric polarization of the IS layer is shown to non-volatily modulate both the AHE and THE. Switching the polarization state ( $P\uparrow$ vs. $P\downarrow$ ) alters the interfacial charge transfer, resulting in distinct electron doping levels (~0.029 e/f.u. vs. ~0.067 e/f.u.). This modifies the Berry curvature distribution and the intrinsic anomalous Hall conductivity without significantly changing the total magnetization or Curie temperature.
Four-State Memory Functionality: By leveraging the independent bistabilities of the ferroelectric polarization and ferromagnetic order, the device achieves four distinguishable Hall resistance states. These states are programmable via electric field (top-gate voltage) and magnetic field pulses, demonstrating a non-volatile four-state memory functionality.

Significance
The paper claims that these findings highlight the potential of ferroelectric/ferromagnetic van der Waals interfaces for advanced device applications. Specifically, the work demonstrates a versatile platform for:

Electrical Tunability: Achieving non-volatile, reversible control over topological spin textures and associated transport phenomena (THE and AHE) via ferroelectric polarization.
Multistate Memory: Realizing a single-cell, two-bit memory device with four distinct, non-volatile resistance states.
Fundamental Insight: Providing a comprehensive picture of how interfacial DMI competes with bulk ferromagnetism in 2D heterostructures and how ferroelectric gating can manipulate the electronic environment to tune magnetic properties.

The authors note that while the current demonstration operates at cryogenic temperatures (below ~40–50 K for optimal state distinguishability), the rich degrees of freedom at vdW interfaces offer strategies for future room-temperature operation, such as strain engineering, electrostatic doping, or pairing with high- $T_c$ magnets. The study establishes a foundation for tunable topological spintronics and multibit memory technologies based on 2D multiferroic heterostructures.

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