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物性・原理

Current-induced Magnetization Switching Using Electrically-insulating Spin-torque Generator

 Keio University announced on February 26, 2018 that the research group led by Associate Professor Kazuya Ando succeeded in demonstrating current-induced magnetization switching using an insulator. The success was based on the collaborative research with Tohoku University, and details were published in Science Advances*.

 Spin is an attribute of electron and its use in addition to electric charge is expected to enable high performance and low-power operation of memory and logic devices. The current-induced magnetization switching through the spin-orbit torques is generally observed in heterostructures with broken inversion symmetry, such as an ultrathin FM (ferrimagnetic material) sandwiched between an oxide and a heavy metal (HM): oxide / FM / HM structures. However, electric current through HM could be against energy- efficient operation. Spin-torque generation through insulator is desirable.

 The research group demonstrated current-induced magnetization switching using electrically-insulating spin-torque generator. The device was composed of a MgO (1.4nm) / CoTb (4.2nm) / Pt (O) (8nm) trilayer on thermally-oxidized Si substrate. HM Pt was deposited on the substrate by RF magnetron sputtering at room temperature in argon and oxygen gas to incorporate O into Pt so that the HM turns into an insulating spin-torque generator. CoTb was selected as FM with perpendicular magnetic anisotropy instead of commonly used CoFeB for better interface stability. Hall effect resistance of the device showed hysteresis loop against electric current through FM under magnetic field between -60mT and +60mT, manifesting magnetization switching by spin-torque generation at the FM/Pt (O) interface.

*Hongyu An, Takeo Ohno, Yusuke Kanno, Yuito Kageyama, Yasuaki Monnai, Hideyuki Maki, Ji Shi, and Kazuya Ando, "Current-induced magnetization switching using electrically-insulating spin-torque generator", Science Advances, 23 Feb 2018, Vol. 4, No. 2, eaar2250; DOI: 10.1126/sciadv.aar2250