Perpendicular magnetic field arises from asymmetric current spreading

Magnetic memory and computing exploit the charge, spin, and orbital degrees of electrons. A strong perpendicular magnetic anisotropy capable of switching via an electrical manner is integral to the development of these technologies. However, conventional materials such as heavy metals and topological insulators can only generate transversely polarized spins resulting in an angular momentum incapable of switching.

Liu and Zhu report that a perpendicular effective magnetic field can exist in magnetic micron devices due to asymmetric current spreading. The magnetic field was found to vary with the geometries of devices and measurements.

“Such perpendicular effective magnetic fields induced by asymmetric current spreading within uniform magnetic heterostructures provides a new, universally accessible mechanism for efficient, scalable, and external-field-free switching of perpendicular magnetization in nonvolatile memory and computing technologies,” said co-author Lijun Zhu.

Using spin torque ferromagnetic resonance, harmonic Hall voltage response, and magnetization switching analyses, the researchers concluded that neglecting a significant current spread results in incorrect conclusions regarding the presence of a perpendicular spin. As a solution, they developed a unified approach to reliably measure the spin-orbit torque efficiencies of different spin polarizations from angle-dependent measurements considering current spreading effects.

“This work advances the understanding of the characterization techniques and helps achieve reliable spin-torque analyses of different spin polarizations,” said Zhu.

Future work will likely focus on the integration scheme of a spin-orbit torque magnetoresistive RAM device with optimized contact geometry to enhance the current spreading effects.

Source: “Current-induced perpendicular effective magnetic field in magnetic heterostructures,” by Qianbiao Liu and Lijun Zhu, Applied Physics Reviews (2022). The article can be accessed at https://doi.org/10.1063/5.0116765 .