In the invisible world of electrons and spins, magnetic materials hold more mysteries than they appear to on the surface. These secrets are slowly being unraveled by a phenomenon first noticed nearly a century and a half ago—a quiet, almost elusive effect that has long lingered in the shadows of its better-known cousin, the ordinary Hall effect. Known as the anomalous Hall effect (AHE), this intricate quantum interaction has just taken center stage, thanks to a groundbreaking breakthrough by researchers at the Chinese Academy of Sciences. Their innovation could fundamentally reshape how we detect and manipulate magnetic fields, offering a tantalizing glimpse into the future of spintronics and ultra-sensitive magnetic sensors.
The Echoes of a 19th-Century Discovery
In 1881, American physicist Edwin Hall discovered something unusual while experimenting with magnetic materials. When an electric current flowed through a conductor in the presence of a magnetic field, it generated a voltage perpendicular to both the current and the magnetic field. This became known as the Hall effect, a phenomenon now fundamental to many magnetic field sensors. But when Hall repeated the experiment with ferromagnetic materials, the transverse voltage appeared even in the absence of an external magnetic field. This effect, he noted, must be tied intrinsically to the material’s own magnetism. Thus was born the anomalous Hall effect.
For decades, the AHE remained scientifically fascinating but practically underwhelming. It offered an intriguing glimpse into the interplay between charge, spin, and magnetism, but its practical usefulness was hampered by one persistent limitation: the anomalous Hall angle (θA).
Why the Anomalous Hall Angle Matters
The anomalous Hall angle is a measure of how efficiently a longitudinal electric current—flowing straight through a material—can be converted into a transverse, spin-polarized Hall current. In other words, it’s a gauge of how well a material can exploit the AHE to generate useful electrical responses in the perpendicular direction.
In conventional ferromagnetic materials, this angle has always been disappointingly small—so small, in fact, that it significantly limits the performance of AHE-based technologies such as magnetic sensors or spintronic devices. With a minuscule θA, only a tiny fraction of the original current contributes to a detectable Hall signal, curbing sensitivity and efficiency.
That’s where the recent work by Dr. Enke Liu and his team enters the spotlight—not as an incremental improvement, but as a radical leap forward.
Magnetic Topology and Weyl Fermions: Enter the Quantum Strangeness
Seven years ago, Liu and colleagues stumbled upon something remarkable in the world of quantum materials: magnetic Weyl fermions. These are not particles in the traditional sense but quasiparticles—collective excitations that behave like chiral, massless electrons within certain crystalline environments. Think of them as ghostly echoes of particles, emerging from the fabric of exotic materials known as topological semimetals.
One such semimetal is Co₃Sn₂S₂, a compound composed of cobalt, tin, and sulfur, with a layered crystal structure and unusual magnetic properties. This material doesn’t just conduct electrons—it warps their momentum space, giving rise to intense Berry curvature, a kind of pseudomagnetic field that exists not in physical space, but in the abstract realm of momentum.
This curvature acts as an internal compass for electrons, nudging them sideways as they travel through the material. It’s this twist in their path that amplifies the anomalous Hall effect. The theory was elegant. The next step was to translate it into reality.
A Model for Modulating the Anomalous Hall Angle
Until recently, the anomalous Hall angle was regarded as a material constant—an unyielding figure dictated by nature. But Liu and his team believed otherwise. In a recent study published in Nature Electronics, they unveiled a new two-variable mathematical model that places θA under human control.
For the first time, the researchers expressed the anomalous Hall angle as a function of longitudinal resistivity and anomalous Hall conductivity—two measurable quantities that can be tuned through experimental design. This model doesn’t just describe behavior; it predicts and guides it.
According to the model, modifying certain intrinsic and extrinsic material parameters—such as topological states, temperature, doping levels, and dimensional confinement—can systematically adjust θA. The beauty lies in its universality: this strategy can, in principle, be applied across a wide variety of magnetic topological materials.
From Theory to Triumph: Giant Anomalous Hall Angle Achieved
Testing their theory, Liu’s team turned again to Co₃Sn₂S₂. Using their model as a guide, they conducted a series of experiments, introducing subtle tweaks to the material’s structure and environment. The results were nothing short of historic.
They achieved a zero-field anomalous Hall angle of 25 degrees—or 46%—a value an order of magnitude greater than any previously recorded in magnetic materials over the past 70 years. To put this in perspective, traditional ferromagnets have θA values closer to 1 or 2 degrees. In the realm of spintronics, this is the equivalent of turning up the volume from a whisper to a thunderclap.
This dramatic increase was not merely academic. It translated directly into real-world performance.
Redefining the Magnetic Sensor
Armed with their newly optimized material, the team developed an anomalous Hall sensor capable of detecting low-frequency magnetic fields with unprecedented sensitivity. At 1 Hz, the sensor achieved a magnetic field detection capability of 23 nT/Hz^0.5 and a Hall sensitivity of 7028 μΩ·cm/T.
These figures are astounding: three times the low-frequency sensitivity and ten times the Hall sensitivity of conventional anomalous Hall sensors. In essence, this device can detect fainter magnetic fields, respond more sharply, and operate with much higher efficiency—all thanks to the manipulated anomalous Hall angle.
What makes this even more impressive is that the sensor operates without requiring an external magnetic field, meaning it functions effectively in ambient conditions—critical for real-world applications in medical diagnostics, geophysical exploration, and next-gen computing.
Toward a Future of Magneto-Electronic Marvels
This discovery is more than a single breakthrough. It’s the beginning of a new design paradigm—a proof-of-principle that the rules of magnetic sensing and spintronics can be rewritten by leaning into the topological quantum nature of materials.
“The key,” Liu explains, “was the realization that topological features—once considered merely theoretical curiosities—can be harnessed to dramatically enhance practical device performance.” This new model doesn’t just help us understand how the anomalous Hall angle works. It gives us a roadmap for controlling it.
Now, the goal is to discover more magnetic topological materials, identify new physical mechanisms, and build devices that exploit these effects at scale. If successful, these innovations could lead to compact, ultra-sensitive magnetic sensors, energy-efficient memory elements, and even components for quantum computers.
Quantum Twists and Topological Turns
At its core, this story is about more than materials and measurements. It’s about the profound intersection of fundamental physics and practical engineering. The anomalous Hall effect—once a subtle curiosity discovered in the late 19th century—has now been supercharged by the strange and beautiful world of topological quantum mechanics.
Weyl fermions, Berry curvature, and spin textures might seem abstract, but they are becoming the tools of a new generation of engineers and physicists. These researchers are not just uncovering nature’s secrets—they’re beginning to reshape them, bending them to serve human needs in ways that defy traditional limitations.
A Vision for the Next Generation
Einstein once said that “the most incomprehensible thing about the universe is that it is comprehensible.” The work of Liu and his team exemplifies this truth. With rigorous thinking and creative modeling, they’ve taken a phenomenon rooted in quantum complexity and turned it into a technological asset.
The anomalous Hall angle, long a bottleneck in magnetic sensing and spintronic design, is no longer a limiting factor. It is now a tunable parameter, a dial that can be turned to amplify sensitivity, improve efficiency, and open the door to magneto-electronic systems that were once the realm of science fiction.
As Liu concludes, “We provide a proof-of-principle demonstration of topology-enhanced high-performance magnetic sensing, expected to advance the application of magnetic topological physics in next-generation magneto-electronics.”
The message is clear: the age of passive materials is ending. The age of designed quantum functionality has just begun.
Reference: Jinying Yang et al, Modulation of the anomalous Hall angle in a magnetic topological semimetal, Nature Electronics (2025). DOI: 10.1038/s41928-025-01364-8.