We present an approach to realize ultrafast field-free spin-orbit torque (SOT) switching of a ferromagnetic layer with perpendicular magnetic anisotropy. In this scheme, the heavy metal layer serves as both the spin Hall channel and the interlayer exchange spacer. The magnetization switching of the adjacent ferromagnetic layer is driven by magnetic inertia, exhibiting intriguing and rich switching behavior under current pulses of different amplitudes and durations. Based on the macrospin simulation, we investigated the switching behavior of the composite-free layer, i.e., two antiferromagnetically coupled ferromagnetic layers, and demonstrated the possibility of field-free switching within tens of picoseconds. Our results show that the positive sign product of field-like SOT and damping-like SOT and the strong antiferromagnetic exchange between the two coupled ferromagnetic layers are critical to realize the deterministic switching. This work is expected to stimulate further experimental efforts for designing high performance magnetic random-access memory application.

A novel method utilizing response surface methodology (RSM) is proposed for effective analysis of the combined influence of writing head geometry and media properties on writing field performance. The method comprises two main modules: (1) a parametric writing head model based on finite element electromagnetic field analysis and (2) an effective writing field gradient model based on RSM. Using the method proposed, the writing performance of an asymmetrically shielded writing head for shingled magnetic recording on bit-patterned media (SMR-BPM) is analyzed. The results show that the shielding trailing gap and medium coercivity primarily impact the effective writing field (EWF) gradient and that the shielding side gap has a secondary impact. More importantly, the analysis shows a strong interaction effect between the influences of writing head geometry and medium coercivity on the EWF gradient, which indicates the need for inclusive design.

As the lateral dimension of spin Hall effect based magnetic random-access memory (SHE-RAM) devices is scaled down, shape anisotropy has varied influence on both the magnetic field and the current-driven switching characteristics. In this paper, we study such influences on elliptic film nanomagnets and theoretically investigate the switching characteristics for SHE-RAM element with in-plane magnetization. The analytical expressions for critical current density are presented and the results are compared with those obtained from macrospin and micromagnetic simulation. It is found that the key performance indicators for in-plane SHE-RAM, including thermal stability and spin torque efficiency, are highly geometry dependent and can be effectively improved by geometric design.