Researchers at Boston College, University of Chemistry and Technology Prague and Japan's National Institute for Materials Science have built a spin transistor that can be switched either electrically or magnetically from within a single two-dimensional device, using the van der Waals magnetic semiconductor chromium sulfur bromide (CrSBr). The device reaches an electrical on/off ratio of a million percent and a magnetic on/off ratio of 3,000 percent, which the team says is well above what prior spin-transistor efforts have achieved.
The work targets the "von Neumann bottleneck": the energy and speed cost of continually shuttling data, including the billions of parameters in large AI models, between separate compute and memory blocks on a chip. A long-standing goal in spintronics is a single "spin transistor" device that combines a magnetic bit with a semiconducting switch, so it can compute and store data at once. Historically, building one has meant physically joining two different materials, a magnet and a semiconductor, together. "By engineering a single van der Waals crystal, CrSBr, that inherently possesses both semiconducting and magnetic properties, we eliminate losses at interfaces entirely," said Zdeněk Sofer, a materials-synthesis specialist at the University of Chemistry and Technology Prague.
The group fabricated the device from two-layer-thick CrSBr, placing laterally separated electrodes on opposite layers of a monolayer-bilayer junction so that current is forced to travel both across and between the magnetic layers, a transport geometry the team describes as mechanistically distinct from the vertical-tunneling junctions typically used in spintronic devices. The layers, encapsulated with hexagonal boron nitride crystals grown by NIMS researchers Kenji Watanabe and Takashi Taniguchi, can be switched on and off either by changing the voltage on a nearby gate electrode or by flipping the two CrSBr layers between parallel and antiparallel magnetic orientation, conceptually similar to a CMOS transistor but with an added magnetic degree of freedom.
To characterize the device, the team paired electrical transport measurements with scanning nitrogen-vacancy (NV) center magnetometry, a quantum sensing technique that maps local magnetic fields by tracking an atomic defect's magnetic resonance. "The major challenge is understanding how magnetism and electrical current interact in nanoscale devices," said Boston College's Brian B. Zhou. "We developed a single-spin quantum microscope to observe magnetic states inside atomically thin devices as they actively process electrical information."
The performance gain traces back to the device operating in a "space-charge-limited" conduction regime, where the buildup and mutual repulsion of charges inside the material produce a power-law current-voltage relationship instead of conventional ohmic, linear behavior. Combining electrostatic gate doping of that space-charge-limited lateral conduction with interlayer exchange coupling between the two CrSBr layers is what produces the device's giant, gate-tunable magnetoresistance. "The rapid power law scaling allows us to dramatically tune the conductivity," said Thomas K. M. Graham, the study's lead author and a graduate student in Zhou's lab. "Our device achieves an electrical on/off ratio of a million percent and a magnetic on/off ratio of 3,000 percent."
The team also identified a field-trainable "layer-sharing" effect that determines whether the device's magnetic layers reverse coherently or through domain-wall motion at the spin-flip transition, which lets the device access multiple, memristive intermediate conductance states rather than just a binary on/off switch, a feature relevant to analog and neuromorphic-style computing. Zhou's group frames the combined switching-logic-plus-nonvolatile-memory architecture as a path toward "instant-on" processors that skip fetching data from separate memory, as well as reconfigurable circuits that could be rewired after manufacturing. Realizing that, Zhou said, will depend on continued advances in nanoscale magnetic imaging and in electrically controlling magnetic states.