Phase diagram and optimal switching induced by spin Hall effect in a perpendicular magnetic layer

Abstract

In a ferromagnet/heavy-metal bilayer device with strong spin Hall effect an in-plane current excites magnetic dynamics through spin torque. We analyze bilayers with perpendicular magnetization and calculate three-dimensional phase diagrams describing switching by external magnetic field at a fixed current. We then concentrate on the case of a field applied in the plane formed by the film normal and the current direction. Here we analytically study the evolution of both the conventional "up"/"down" magnetic equilibria and the additional equilibria created by the spin torque. Expressions for the stability regions of all equilibria are derived, and the nature of switching at each critical boundary is discussed. The qualitative picture obtained this way predicts complex hysteresis patterns that should occur in bilayers. By analyzing the phase portraits of the system we show that when the spin torque induced equilibrium exists, switching between "up" and "down" states proceeds through it as an intermediate state. Using numeric simulations we analyze the switching time and compare it to that of a conventional spin torque device with collinear magnetizations of the polarizer and the free layer.

arXiv comment12 pages, 10 figures

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Cited by in corpus (8)

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• Spin transfer torques due to the bulk states of topological insulators
• Angular dependence of spin-orbit torque in monolayer $F{e}_{3}GeT{e}_2$
• Tuning the perpendicular magnetic anisotropy, spin Hall switching current density and domain wall velocity by submonolayer insertion in Ta / CoFeB / MgO heterostructures
• Current-Induced Instability of a Perpendicular Ferromagnet in Spin Hall Geometry
• Coherent Sub-Nanosecond Switching of Perpendicular Magnetization by the Field-like Spin-Orbit Torque without an External Magnetic Field