Anomalous Hall Torque: “Completely New Physics” for Next Generation Spintronics

The first spintronics prototype device in history that utilizes the anomalous Hall torque effect. Credit: Nature Nanotechnology (2025). DOI: 10.1038/s41565-024-01819-7
A data-driven world demands more capacity, more efficiency, and more computing power. To meet society’s insatiable need for electron speed, physicists have promoted the burgeoning field of spintronics.
Traditional electronic devices use electronic charges to encode, store, and transmit information. Spintronic devices exploit both the charge and spin orientation of electrons. By assigning values to electron spins (top = 0, bottom = 1), spintronic devices provide an ultrafast and energy-efficient platform.
To develop viable spintronics, physicists need to understand the quantum properties within materials. One property, known as spin torque, is important for the electrical manipulation of magnetization needed for next generation storage and processing technologies.
Researchers at the University of Utah and the University of California, Irvine (UCI) have discovered a new type of spin-orbit torque. The study, published in Nature Nanotechnology on January 15, 2025, demonstrates a new way to manipulate spin and magnetization through electric current, a phenomenon called anomalous Hall torque.
“This is entirely new physics, which is interesting in and of itself, but it also has a lot of potential new applications along with it,” said David E., assistant professor of physics and astronomy at the University of Utah and lead author of the paper. said one Eric Montoya. study. “These self-generated spin torques are uniquely qualified for new types of computing, such as neuromorphic computing, an emerging system that mimics human brain networks.”
torque hole
Electrons have a minimal magnetic field and are dipoles, just like the Earth. Some spins point north (“up”) or south (“down”), or somewhere in between. Like magnets, opposite poles attract and like poles repel. Spin orientation torque refers to the speed at which an electron rotates around a fixed point.
In some materials, electricity sorts electrons based on their spin orientation. The distribution of spin orientation, known as symmetry, affects the properties of materials, such as the flow in the direction of the magnetic field in ferromagnets.
Anomalous Hall torque is related to the well-known anomalous Hall effect, discovered by Edwin Hall in 1881. The anomalous Hall effect explains how electrons scatter asymmetrically as they pass through a magnetic material, causing a charging current to flow through the magnetic material through 90 degrees. External current flow. As it turns out, a similar process occurs with spin. When an external current is applied to a material, a spin current flows at 90 degrees to the current flow, with the spin orientation along the direction of magnetization.
“At the end of the day, it’s about symmetry. The various Hall effects represent a symmetry in how efficiently we can control the spin orientation of a material,” Montoya said. “You can have one effect or you can have all effects in the same material. As material scientists, we can actually tune these properties to make the device behave differently. can.”
Three torques for spintronic devices
The anomalous Hall torque is an example of a new concept in spintronics known as self-generated spin-orbit torque, which exhibits a unique spin-torque symmetry that is ideal for supporting future spintronic devices. Together with the spin Hall torque and the recently identified planar Hall torque discovered by a team that also included co-author Montoya and UCI physicist Ilya Krivorotov, the anomalous Hall torque is one of three Hall-like spin-orbit torques. Complete the set.
Because the torque triad should exist in all conductive spintronic materials, the authors named them “universal Hall torques.” Their universality provides researchers with powerful tools to develop spintronic devices.
Traditional spintronics typically consist of a nonmagnetic layer sandwiched between two ferromagnetic materials, such as magnetoresistive random access memory (MRAM). Spin-torque MRAM stores and manipulates data by injecting spin-polarized current from one magnetic layer to a second magnetic layer. This reverses the spin direction of the second magnetic layer.
The spin orientation “up” or “down” can be mapped to 0 and 1, which are used to store binary data. Spin-torque MRAM can store and access data faster and more efficiently than traditional MRAM, which relies on magnetic fields to reverse flow.
The authors demonstrated that their device can transfer spin orientation from a ferromagnetic conductor to an adjacent nonmagnetic material, eliminating the need for a second ferromagnetic layer. In fact, the authors have constructed the first-ever spintronics prototype that utilizes the anomalous Hall torque effect.
“We harnessed the anomalous Hall torque to create a nanoscale device known as a spin-torque oscillator. This device can mimic the functionality of neurons, but is significantly smaller and operates at higher speeds. ”Krybolotov said. “Our next step is to explore the possibility of interconnecting these devices into larger networks to perform neuromorphic tasks such as image recognition.”
Further information: Eric Arturo Montoya et al, Anomalous Hall spin current drives self-generated spin-orbit torque in ferromagnets, Nature Nanotechnology (2025). DOI: 10.1038/s41565-024-01819-7
Provided by University of Utah
Citation: Anomalous Hall Torque: “A Whole New Physics” for Next Generation Spintronics (January 16, 2025), https://phys.org/news/2025-01-anomalous-hall-torque-brand-physics Retrieved January 16, 2025 from.html
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