🔬 applied physics

Electric-current control of anomalous Hall effect

This study demonstrates robust and reversible electric-current control of the anomalous Hall effect in a WTe2/Fe3GeTe2 heterostructure, where a charge current in WTe2 induces an out-of-plane magnetization via the Berry-curvature dipole that modulates the adjacent ferromagnet's properties through the inverse magnetic proximity effect.

Original authors: Jianping Guo, Gusthavo M. S. Brizolla, Peng Rao, Jian Shao, X. H. Huang, Thomas N. G. Meier, Tailai Xu, Peirui Ji, Jonathan Finley, Jaroslav Fabian, Johannes Knolle, Christian Back, Lin Chen

Published 2026-08-28

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CC BY 4.0

Original authors: Jianping Guo, Gusthavo M. S. Brizolla, Peng Rao, Jian Shao, X. H. Huang, Thomas N. G. Meier, Tailai Xu, Peirui Ji, Jonathan Finley, Jaroslav Fabian, Johannes Knolle, Christian Back, Lin Chen

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

In the world of electronics, the flow of electricity is usually a one-way street for information: a current moves through a wire, and that movement carries a signal. But in certain special materials, electricity can do something more subtle. When a current passes through a magnetic metal, it can generate a sideways voltage, a phenomenon known as the anomalous Hall effect. This effect acts like a built-in compass for the material's internal magnetism; the stronger the magnetism points up or down, the larger the sideways voltage becomes. For decades, scientists have used this effect to measure magnetic properties, but they have struggled to do the reverse: to use electricity to actively change the magnetism itself. Traditional methods to tweak magnetism require bulky equipment or complex structures that are difficult to build. The goal has been to find a way to control this magnetic signal with a simple electric current, much like turning a knob to adjust the volume on a radio.

A team of researchers has now demonstrated a robust way to achieve this control using a stack of two ultra-thin, two-dimensional materials. They placed a layer of a magnetic metal called Fe3GeTe2 on top of a layer of a material called WTe2. When they sent an electric current through the WTe2 layer, it did not just flow; it generated a tiny, invisible magnetic field pointing straight up or down, depending on the direction of the current. This induced field reached out to the magnetic layer sitting on top and altered its internal magnetic strength. The result was a dramatic change in the sideways voltage produced by the magnetic layer. By simply reversing the direction of the current, the researchers could increase the magnetic signal by more than 180 percent or suppress it almost entirely. This is a level of control that far exceeds what has been achieved with previous methods, which typically managed changes of only 40 to 100 percent.

The secret to this powerful effect lies in the unique atomic structure of the WTe2 layer. Unlike many materials where atoms are arranged in perfect, symmetrical patterns, the WTe2 used here has a specific, lower-symmetry arrangement. When an electric current flows through this specific direction, it creates a dipole in the electronic structure, a kind of imbalance that forces the electrons to generate an out-of-plane magnetic moment. The researchers found that this effect is strongest when the WTe2 layer is exactly two atomic sheets thick. If the layer is a single sheet, the effect vanishes because the symmetry is too high. If the layer is thicker, the effect weakens as the extra layers dilute the unique properties of the surface. This precise thickness dependence confirmed that the phenomenon is an interfacial effect, born from the specific interaction between the layers and the unique electronic behavior of the two-layer WTe2.

To prove that this was a genuine magnetic control and not just a side effect of heat, the team performed several rigorous checks. They showed that the effect disappears if the current is sent through the WTe2 in the wrong direction, along a high-symmetry axis where the special magnetic generation does not occur. They also tested a device made of only the magnetic material, without the WTe2 layer, and found no such modulation, ruling out the possibility that the current was simply heating the magnet and changing its properties. Furthermore, they demonstrated that the change in the signal was reversible and could be switched back and forth simply by flipping the current's direction, without needing any external magnets to assist the process. The magnitude of the change was so large that the device behaves like a transistor, where the electric current acts as the gate to control the flow of the magnetic signal.

This discovery opens a new path for manipulating static magnetism without moving parts or complex wiring. Because the method relies on the flow of current rather than the transfer of electrons between materials, it could potentially be used to control magnetic insulators, which are materials that do not conduct electricity but still possess magnetic order. This capability could be crucial for future technologies, such as improving the stability of magnetic memory or creating new types of electronic switches. The researchers suggest that this approach could even be extended to more exotic materials, potentially raising the temperature at which certain quantum effects can be observed. By showing that a simple electric current can drastically reshape the magnetic landscape of a material, this work provides a powerful new tool for the next generation of spintronic devices.

Technical Summary: Electric-current control of anomalous Hall effect

Problem and Motivation
The anomalous Hall effect (AHE) is a fundamental phenomenon in condensed matter physics where a transverse voltage develops in ferromagnetic materials without an external magnetic field. The AHE conductivity ( $\sigma_{AHE}$ ) is intrinsically linked to the Berry curvature (BC) of the electronic band structure. While the AHE is widely used to characterize magnetic properties, the underlying electronic band structure—and consequently the BC and $\sigma_{AHE}$ —is typically fixed once a magnetic material is prepared. Existing methods to tune the AHE, such as electrostatic gating or ionic gating, are often limited by complex device architectures and the charging/discharging capacity of the gate, resulting in modest modulation degrees. There is a need for efficient, reversible, and simpler methods to electrically tune the Berry curvature and the resulting AHE, particularly for applications in spintronics and the control of static magnetism.

Methodology
The authors fabricated two-dimensional heterostructures consisting of a transition-metal dichalcogenide, $T_d$ -WTe $_2$ , stacked on a ferromagnetic metal, Fe $_3$ GeTe $_2$ (FGT). The study utilized a stack where the WTe $_2$ thickness ( $t_{WTe}$ ) was varied down to the monolayer limit, and the FGT thickness ( $t_{FGT}$ ) was also systematically adjusted.

The experimental approach involved passing a direct current ( $I$ ) through the WTe $_2$ layer while simultaneously applying a small alternating current ( $I_{ac}$ ) to detect the transverse voltage. The key mechanism investigated is the generation of an out-of-plane magnetization ( $M_z^I$ ) in the WTe $_2$ layer via the Berry curvature dipole (BCD) when a charge current flows along the low-symmetry $a$ -axis. This current-induced $M_z^I$ acts on the adjacent FGT layer.

The researchers performed control experiments to isolate the effect:

Measuring pure FGT samples to rule out intrinsic current effects in the ferromagnet.
Varying the current direction relative to the WTe $_2$ crystal axes (comparing the low-symmetry $a$ -axis with the high-symmetry $b$ -axis).
Systematically varying the thickness of both the WTe $_2$ and FGT layers to determine the spatial origin of the modulation.
Conducting first-principles density functional theory (DFT) calculations to model the relationship between exchange splitting and AHE conductivity.

Key Contributions and Results
The study demonstrates a robust and reversible electric-current control of the AHE in the WTe $_2$ /FGT stack. The primary findings include:

Giant Modulation: Applying a current through the WTe $_2$ layer induces a modulation of the AHE conductivity in the adjacent FGT layer. The relative change in AHE conductivity ( $\Delta\sigma_{AHE}/\sigma_{AHE}(0)$ ) exceeds 180%, a value significantly higher than previous methods (e.g., static gating ~40% or high pressure ~100%). Unlike pressure, which only suppresses AHE, this method allows for bidirectional control (enhancement and suppression).
Mechanism via Berry Curvature Dipole (BCD): The modulation is driven by the BCD in few-layer WTe $_2$ $_{2}$ . The current $I$ $I$ generates an out-of-plane magnetization $M_z^I$ $M_{z}^{I}$ via the BCD. This $M_z^I$ $M_{z}^{I}$ couples with the FGT magnetization ( $M$ $M$ ) through an effective exchange magnetic field, modulating the effective exchange splitting ( $E_{ex}$ $E_{e x}$ ) of the FGT.
- When $M_z^I$ and $M$ are parallel, $E_{ex}$ increases, enhancing the Berry curvature and $\sigma_{AHE}$ .
- When they are anti-parallel, $E_{ex}$ decreases, reducing $\sigma_{AHE}$ .
Thickness Dependence:
- WTe $_2$ Thickness: The modulation peaks for bilayer WTe $_2$ and is negligible for monolayers or thick films. This aligns with the BCD magnitude, which is maximized in bilayers due to broken inversion symmetry and layer-polarized Dirac fermions.
- FGT Thickness: The modulation amplitude decreases as the FGT thickness increases, confirming the interfacial origin of the effect.
Control Experiments:
- No modulation is observed in pure FGT samples.
- No modulation occurs when the current is applied along the high-symmetry $b$ -axis of WTe $_2$ , confirming the symmetry requirement for BCD generation.
- The current-induced Hall signal in pure WTe $_2$ is at least 13 times smaller than the modulation observed in the stack, ruling out a direct contribution from WTe $_2$ to the measured signal.
Exclusion of Joule Heating: The authors demonstrate that the observed odd-function dependence of $\sigma_{AHE}$ on current cannot be attributed to Joule heating, which would produce an even-function dependence and a much smaller magnitude of change.

Significance and Claims
The paper claims that this work reveals the Berry curvature dipole in low-dimensional material systems as a highly efficient mechanism for spintronic applications. The demonstrated method offers a new pathway for the control of static magnetism, specifically proposing the realization of AHE-transistors where the charge current serves as the gate and the transverse AHE signal as the channel.

Furthermore, the authors suggest that this approach, which does not rely on electron filling or transfer, opens new avenues for controlling quantum magnetic insulators. Potential applications mentioned include:

Raising the observation temperature of the quantum anomalous Hall effect in magnetic topological insulators by tuning the exchange gap.
Driving topological insulators into magnetic Weyl semimetal states.
Tuning the separation between Weyl points.

The authors note that while the proposed two-band model captures the essential physics, the mechanism may be oversimplified, and further theoretical studies are required to fully understand the current-generated torques and effective exchange fields. They also suggest that even larger modulations could be achieved with improved devices capable of sustaining higher currents or by exploring materials with stronger BCDs.

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