A review of current research on spin currents and spin–orbit torques

Spintronics is a new discipline focusing on the research and application of electronic spin properties. After the discovery of the giant magnetoresistance effect in 1988, spintronics has had a huge impact on scientific progress and related applications in the development of information technology. In recent decades, the main motivation in spintronics has been efficiently controlling local magnetization using electron flow or voltage rather than controlling the electron flow using magnetization. Using spin-orbit coupling in a material can convert a charge current into a pure spin current(a flow of spin momenta without a charge flow) and generate a spin-orbit torque on the adjacent ferromagnets. The ability of spintronic devices to utilize spin-orbit torques to manipulate the magnetization has resulted in large-scale developments such as magnetic random-access memories and has boosted the spintronic research area. Here in, we review the theoretical and experimental results that have established this subfield of spintronics. We introduce the concept of a pure spin current and spin-orbit torques within the experimental framework, and we review transport-, magnetization-dynamics-, and opticalbased measurements and link then to both phenomenological and microscopic theories of the effect. The focus is on the related progress reported from Chinese universities and institutes, and we specifically highlight the contributions made by Chinese researchers.

High Resolution Microwave B-Field Imaging Using a Micrometer-Sized Diamond Sensor

We propose a diamond-based micron-scale sensor and perform high-resolution B-field imaging of the near-field distribution of coplanar waveguides.The sensor consists of diamond crystals attached to the tip of a tapered fiber with a physical size on the order of submicron.The amplitude of the B-field component B is obtained by measuring the Rabi oscillation frequency.The result of Rabi sequence is fitted with a decayed sinusoidal.We apply the modulation-locking technique that demonstrates the vector-resolved field mapping of the micromachine coplanar waveguide structure(CPW).B-field line scan was performed on the CPW with a scan step size of 1.25μm.To demonstrate vector resolved rf field sensing,a full field line scan acts(was performed)along four NV axes at a height of 50μm above the device surface.The simulations are compared with the experimental results by vector-resolved measurement.This technique allows the measurement of weak microwave signals with a minimum resolvable modulation depth of 20 ppm.The sensor will have great interest in micron-scale resolved microwave B-field measurements,such as electromagnetic compatibility testing of microwave integrated circuits and characterization of integrated microwave components.