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Current induced spin–orbit torque (SOT) switching of magnetization is a promising technology for nonvolatile spintronic memory and logic applications. In this work, we systematically investigated the effect of Ta thickness on the magnetic properties, field-free switching and SOT efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer with perpendicular magnetic anisotropy. We found that both the anisotropy field and coercivity increase with increasing Ta thickness from 0.15 nm to 0.4 nm. With further increase of Ta thickness to 0.5 nm, two-step switching is observed, indicating that the two magnetic layers are magnetically decoupled. Measurements of pulse-current induced magnetization switching and harmonic Hall voltages show that the critical switching current density increases while the field-free switching ratio and SOT efficiency decrease with increasing Ta thickness. Both the enhanced spin memory loss and reduced interlayer exchange coupling might be responsible for the β DL decrease as the Ta spacer thickness increases. The studied structure with the incorporation of a CoFeB layer is able to realize field-free switching in the strong ferromagnetic coupling region, which may contribute to the further development of magnetic tunnel junctions for better memory applications.

The current-induced magnetization switching and damping-like field in Pt/(Co/Pt)/PtMn trilayer films prepared with and without an

A sensitive DC magnetic field sensor is constructed by measuring the signal-to-noise ratio of an AC-modulated magnetic field at a particular frequency from an optical whispering gallery mode microcapillary resonator. The sensing element consists of an optical whispering gallery mode microcapillary resonator bonded to a magnetostrictive material that enables it to respond to external magnetic fields. A DC magnetic field sensitivity of 0.1703dB/Oe and a linear detection range from 4.8Oe to 65.7Oe are realized under an AC modulation field of 168.1kHz in the unshielded environment at room temperature. To our best knowledge, this sensitivity is about 2.3 times of the maximum sensitivity of other DC magnetic field sensors based on magnetic fluid or magnetostrictive material integrated fiber systems that use the dissipative sensing scheme. Furthermore, the sensor can operate at a stable temperature in the range of [-11∼45]°C, as long as the modulation frequency of the AC-modulation field is adjusted according to the ambient temperature. This sensor provides us with a novel DC magnetic field sensing scheme, which may play a role in industrial fields related to current and position detection in the future.

Vertically coupled magnetic vortices with potential applications in data storage and processing have attracted great interests in the past two decades. A nonlinear device with short-term memory and controllable activation states is also demanded for neuromorphic computing. In this paper, we investigate the dynamics of vertically coupled vortices with different magnetic configuration excited by a charge current with tilted spin polarization through micromagnetic simulations. It is found that the critical current for the gyration of coupled vortices with parallel polarity is one order larger than that with antiparallel polarity. The eigen-frequency of coupled vortices with parallel polarity is much lower than that with antiparallel polarity. With increasing the inter-disk spacer thickness, the gyration amplitude of vortex with antiparallel polarity becomes smaller. Furthermore, a switching phase diagram study shows that the relative polarity of coupled disks can be manipulated by passing sequential pulse currents. Those results indicate that in a coupled vortex system, the excitation states can be manipulated by controlling the relative polarity (through the applying of currents) and the spacer thickness between them. Our findings provide a device which is more similar to the neurons in human’s brain and being potentially used in spintronic neuromorphic computing.