Farzad Mahfouzi

Microwave-driven ferromagnet–topological-insulator heterostructures: The prospect for giant spin battery effect and quantized charge pump devices

We study heterostructures where a two-dimensional topological insulator (TI) is attached to two normal metal (NM) electrodes while an island of a ferromagnetic insulator (FI) with precessing magnetization covers a portion of its lateral edges to induce time-dependent exchange field underneath via the magnetic proximity effect. When the FI island covers both lateral edges, such device pumps pure spin current in the absence of any bias voltage, thereby acting as an efficient spin battery with giant output current even at very small microwave power input driving the precession. When only one lateral edge is covered by the FI island, both charge and spin current are pumped into the NM electrodes. We delineate conditions for the corresponding conductances (current-to-microwave-frequency ratio) to be quantized in a wide interval of precession cone angles, which is robust with respect to weak disorder and can be further extended by changes in device geometry.

Antidamping spin-orbit torque driven by spin-flip reflection mechanism on the surface of a topological insulator: A time-dependent nonequilibrium Green function approach

Motivated by recent experiments observing spin-orbit torque (SOT) acting on the magnetization

Charge pumping by magnetization dynamics in magnetic and semimagnetic tunnel junctions with interfacial Rashba or bulk extrinsic spin-orbit coupling

\vec{m}

Spin-to-charge conversion in lateral and vertical topological-insulator/ferromagnet heterostructures with microwave-driven precessing magnetization

of a ferromagnetic (F) overlayer on the surface of a three-dimensional topological insulator (TI), we investigate the origin of the SOT and the magnetization dynamics in such systems. We predict that lateral F/TI bilayers of finite length, sandwiched between two normal metal leads, will generate a large antidamping-like SOT per very low charge current injected parallel to the interface. The large values of antidamping-like SOT are {\it spatially localized} around the transverse edges of the F overlayer. Our analysis is based on adiabatic expansion (to first order in

Signatures of electron-magnon interaction in charge and spin currents through magnetic tunnel junctions: A nonequilibrium many-body perturbation theory approach

\partial \vec{m}/\partial t

Spin-charge conversion in a multiterminal Aharonov-Casher ring coupled to precessing ferromagnets: A charge-conserving Floquet nonequilibrium Green function approach

) of time-dependent nonequilibrium Green functions (NEGFs), describing electrons pushed out of equilibrium both by the applied bias voltage and by the slow variation of a classical degree of freedom [such as

HOW TO CONSTRUCT THE PROPER GAUGE-INVARIANT DENSITY MATRIX IN STEADY-STATE NONEQUILIBRIUM: APPLICATIONS TO SPIN-TRANSFER AND SPIN-ORBIT TORQUES

\vec{m}(t)

Intrinsic damping phenomena from quantum to classical magnets: An ab initio study of Gilbert damping in a Pt/Co bilayer

]. From it we extract formulas for spin torque and charge pumping, which show that they are reciprocal effects to each other, as well as Gilbert damping in the presence of SO coupling. The NEGF-based formula for SOT naturally splits into four components, determined by their behavior (even or odd) under the time and bias voltage reversal. Their complex angular dependence is delineated and employed within Landau-Lifshitz-Gilbert simulations of magnetization dynamics in order to demonstrate capability of the predicted SOT to efficiently switch

Current-induced damping of nanosized quantum moments in the presence of spin-orbit interaction

\vec{m}

Spin-orbit torque-driven magnetization switching in 2D-topological insulator heterostructure

of a perpendicularly magnetized F overlayer.