Switching of magnetic memory bits with magnons

Magnetization switching remains one of the central applications of spintronic devices.

“Useful devices, such as magnetic memory or logic circuits, require the ability to switch individual magnetic bits without disturbing neighboring ones,” explains Mehrdad Elyasi, a member of AIMR. “This means technologically relevant solutions must not require global magnetic fields or high-power current inputs to achieve localized deterministic switching.”

To this end, a promising approach uses quasiparticles called magnons—wave-like magnetic disturbances that, in principle, can be confined, guided, or even generated locally, particularly using patterned nanostructures or pulsed excitations.

However, recent work on materials with perpendicular magnetic anisotropy (PMA)—ideal for high-density memory—showed that magnons could only switch magnetization reliably in the presence of an external magnetic field.

To overcome this, researchers needed a way to produce a controlled, out-of-plane spin-polarized magnon currents strong enough to deterministically switch PMA materials—without relying on external fields.

In a 2024 article published in Nature Nanotechnology, Elyasi and co-workers addressed this challenge by exploiting the crystal symmetry and spin canting angle of WTe₂ to generate the desired magnon torque in a WTe₂/NiO/CoFeB heterostructure¹. The team used the low symmetry of WTe₂ to produce spin-polarized electrons with both in-plane and out-of-plane components, which were injected into the adjacent NiO layer. The NiO antiferromagnetic insulator then converted the spin current into magnon currents, preserving their original polarization direction—a slight out-of-plane canting angle of approximately 8.5°.

“The out-of-plane tilt, preserved by the optimal NiO thickness of 25 nanometers, is the crucial feature that provides the anti-damping magnon torque required for deterministic switching of the CoFeB ferromagnet’s perpendicular magnetization without any external magnetic field,” says Elyasi. “Moreover, by acting as an insulating spacer, the NiO layer helps address thermal stability concerns by reducing the impact of Joule heating on the CoFeB layer—a key challenge as magnetic elements scale down.”

In addition to demonstrating field-free switching of perpendicular magnetization at room temperature with a critical current density as low as 4 × 10⁶ A/cm², the authors further showed that introducing a PtTe2 layer enhances in-plane conductivity while preserving the out-of-plane spin canting—reducing power consumption by a factor of 190 compared to earlier systems.

These results suggest that exploiting crystal symmetry and spin canting accompanied by magnon transport enables robust, energy-efficient switching. The work provides a blueprint for future low-power spintronic memory devices based on magnon currents.

As a next step, the researchers plan to investigate how nonlinear interactions between magnons may further contribute to spin angular momentum transfer from NiO to the magnetic layer.