Hokkaido University demonstrates world's first topological Hall torque caused by Weyl points that can be applied to magnetization reversal

A research group led by Associate Professor Michihiko Yamanouchi of the Graduate School, Faculty of Information Science and Technology, Hokkaido University, in collaboration with Dr. Yasufumi Araki, a MEXT Distinguished Researcher at the Advanced Science Research Center, Japan Atomic Energy Agency, and Dr. Jun'ichi Ieda, Senior Scientist also at the Advanced Science Research Center, has demonstrated a new principle that can be applied to reversing the direction of magnetization using electricity in an oxide magnet with a special electronic state called the Weyl point in strontium ruthenate (SrRuO₃).

The technique of electrically reversing the direction of a magnet (magnetization) using current-induced magnetic wall movement is expected to be applied to the writing of information in magnetic memory. In SrRuO₃, it was known that this electrical magnetic wall transfer could be highly efficient, but its cause remained unknown.

The research group fabricated a device that forms a domain wall in SrRuO₃ and by studying how the magnetic field required for the movement the domain wall changes with electric current, they found the effective magnetic field exerted by the current on the domain wall and investigated the temperature dependence of the effective magnetic field in detail over a wide temperature range.

They found that the effective magnetic field increases with decreasing temperature, but at lower temperatures than a certain range, it shows a peculiar temperature dependence with two peaks. Moreover, since the magnitude of the effective magnetic field is larger than the calculated value based on conventional principles, the effective magnetic field in SrRuO₃ is a new principle that cannot be explained by conventional ideas. Furthermore, a comparison of the theoretical and experimental results of the new principle torque (topological Hall torque) due to Weyl points shows that the peculiar temperature dependence and magnitude of this effective magnetic field can be sufficiently explained by topological Hall torque.

The results indicate that the current-induced domain wall migration in SrRuO₃ is mainly due to topological Hall torque caused by Weyl points. The effective magnetic field due to topological Hall torque has been theoretically demonstrated but not verified through experiments. This is the first time that such an effective magnetic field has been observed.

"Since a relatively large number of magnets with similar Weyl points to SrRuO₃ have been found, I hope that they can be applied to magnetic memory for faster and lower power consumption than conventional magnetic memory," says Dr. Yamanouchi.