Spin Hall Switching Enabled by Uniaxial In-Plane Magnetocrystalline Anisotropy

We present a new method for stabilization of magnetic devices: in-plane uniaxial magnetocrystalline anisotropy, achieved through epitaxial growth of a magnetic thin film on a single-crystal substrate. This paradigm enables the creation of in-plane spin orbit torque magnetic random access memory (SOT-MRAM) devices that function without external fields and exhibit the same scalability as perpendicular SOT-MRAM. Through theoretical derivations and numerical simulations based on the Landau-Lifshitz-Gilbert (LLG) equation with spin transfer torque, we show that switching of such devices can be optimized by varying the angle between the injected spin current and the crystalline easy axis, and contrast this angular dependence with the Stoner-Wohlfarth model. Furthermore, we demonstrate rich and complex magnetization dynamics in this system, including strong and tunable dependence on bulk and interfacial magnetoresistance and boundaries between stochastic and deterministic switching. Finally, we present a concept that couples our in-plane anisotropy layer with an out-of-plane ferromagnet to achieve out-of-plane field-free SOT-MRAM switching. We quantify regions of operation for this new device and link them to simulation results for the in-plane layer alone.