Spin-Torque and Spin-Hall Nano-Oscillators

Abstract

This paper reviews the state of the art in spin-torque and spin Hall effect driven nano-oscillators. After a brief introduction to the underlying physics, the authors discuss different implementations of these oscillators, their functional properties in terms of frequency range, output power, phase noise, and modulation rates, and their inherent propensity for mutual synchronization. Finally, the potential for these oscillators in a wide range of applications, from microwave signal sources and detectors to neuromorphic computation elements, is discussed together with the specific electronic circuitry that has so far been designed to harness this potential.<p>QS 2016</p

Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions

“…Magnetic tunnel junctions (MTJs) [1][2][3][4] are multilayer stacks consisting of two ferromagnetic (FM) layers separated by an insulating tunnel barrier. The advantage of MTJs is their high tunnel magnetoresistance (TMR), [3][4][5][6] which enables spintronic applications such as spin-transfer torque magnetoresistive random access memory (STT-MRAM), 7-11 spintorque nano-oscillators (STNOs), [12][13][14][15][16] and neuromorphic computing. 17,18 Recently, voltagecontrolled magnetic anisotropy (VCMA) [19][20][21][22][23][24] was demonstrated in MTJ structures, which is very promising for next-generation devices, including highly energy-efficient magnetoelectric RAM (MeRAM).…”

Low operational current spin Hall nano-oscillators based on NiFe/W bilayers

“…1 These SHNOs operate on the basis of spin-orbit torque (SOT), 2 which is produced when a spin current, created via the spin Hall effect [3][4][5][6][7][8] in a metal with high spin-orbit coupling (e.g., Pt, 9 W, 10,11 Ta 12 ), is absorbed by an adjacent ferromagnetic layer. SOT can act as a negative spin-wave damping in the ferromagnet and above a certain threshold current, it can sustain a steady state autooscillation of the local magnetization.…”

Merging magnetic droplets by a magnetic field pulse

“…[1][2][3][4][5] Under sufficiently large currents, the intrinsic damping torque can be compensated by the spin-transfer torque (STT) 6,7 generated in such contacts in the free layer of spin valves or magnetic tunnel junctions, giving rise to coherent oscillations. For a STO magnetized in the film plane, a self-localized "bullet mode" can be excited depending on the applied magnetic field angle.…”