A torque on conventional magnetic wisdom

phys.org | 7/22/2019 | Staff
JimmyJoe (Posted by) Level 3
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Physicists at the University of Illinois at Urbana-Champaign have observed a magnetic phenomenon called the "anomalous spin-orbit torque" (ASOT) for the first time. Professor Virginia Lorenz and graduate student Wenrui Wang, now graduated and employed as an industry scientist, made this observation, demonstrating that there exists competition between what is known as spin-orbit coupling and the alignment of an electron spin to the magnetization. This can be thought of as analogous to the anomalous Hall effect (AHE).

For a long time now, physicists have known about interesting phenomena such as the AHE in which spins of a certain species accumulate on a film edge. Their accumulations are detectable with electric measurements. This type of experiment requires the magnetization of the film to point perpendicular to the plane of the film. In fact, the Hall effect and similar experiments such as the AHE in the past all use an applied magnetic field (for non-magnetic samples) or the magnetization of the film (for magnetic samples), always perpendicular to the plane of the film.

Effects - AHE - Magnetizations - In-plane

Effects like the AHE had not been found for magnetizations that point in-plane, until now.

By taking advantage of the magneto-optic Kerr effect (MOKE), which can probe the magnetization near the surface of a magnetic sample, Wang and Lorenz demonstrated that an electrical current modifies the magnetization near the surface of a ferromagnetic sample to point in a direction different from the magnetization of the interior of the sample. It is not necessarily strange that the magnetization near the surface can differ from that in the interior, as evidenced by previous experiments in spin-orbit torque. However, the Illinois researchers used a purely ferromagnetic film, whereas past experiments in spin-orbit torque combined ferromagnets with metals that have a property called "spin-orbit coupling."

Discovery - Implications - Technology

This discovery has implications for energy-efficient magnetic-memory technology.

The team's findings are published...
(Excerpt) Read more at: phys.org
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