Spin Doctors: Scientists Observe New Magnetic Phenomenon
By Dawn Allcot
Physicists at the University of Illinois at Urbana-Champaign revealed new findings that put their beliefs about how magnets behave into something of a tailspin – and could change the way we store data in the future.
To understand the new discovery, it’s important to understand the basics of the Hall effect and similar magnetic phenomena.
Sometime after 1879 when New England-based physicist Edwin Hall discovered the Hall effect, which relates to the electric field produced as a transverse of a material’s density and the applied magnetic field. scientists noted a phenomenon called the anomalous Hall effect (AHE). When the AHE is observed, spins of a certain species accumulate on a film edge. The 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 used 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 like the AHE had not been found for magnetizations that point in-plane until recently. Scientists at the University of Illinois at Urbana-Champaign began observing a magnetic phenomenon called the “anomalous spin-orbit torque” (ASOT) for the first time. Professor Virginia Lorenz and graduate student Wenrui Wang demonstrated that there exists competition between what is known as spin-orbit coupling and the alignment of electron spin to the magnetization. The observation is analogous to the AHE.
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.”
The discovery has implications for energy-efficient magnetic-memory technology, taking us beyond solid-state drives to smaller, more efficient magnetic storage. As our electronic devices become smaller and more portable, this research could lead to tremendous advances in both industrial computers and consumer electronics.