Soft X-ray microscope observation of spin-torque-induced vortex gyration

Spintronics is now one of the most important keywords in modern sciences and technologies. The currently employed method for magnetic recording uses electrical current pulses, and there appear to be limitations for extremely high density devices (e.g., G-bit level MRAM). One of the most promising solutions is the use of spin polarized current in a ferromagnetic medium, which can provide a spin-transfer torque to the magnetization, resulting in its motion. To develop high-density and very fast devices, it is indispensable to obtain a fundamental understanding of what really takes place there. Recently, a research group led by Dr. G. Meier (Hamburg University, Germany) succeeded in visualizing spin-torque-induced vortex gyration in micrometer-sized permalloy squares using a 30nm-resolution X-ray microscope at the Advanced Light Source (ALS), Berkeley, United States. The phases of the gyration in structures with different chirality have been analyzed considering alternating spin-polarized currents and the current's Oersted field. For more information on the present experiments, see the paper, "Time-Resolved X-Ray Microscopy of Spin-Torque-Induced Magnetic Vortex Gyration", M. Bolte et al., Phys. Rev. Lett., 100, 1701 (2008).