Spintronic Oscillator Based on Spin-Current Feedback Using the Spin Hall Effect
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As spintronics continues to replace conventional electronics, devices that produce oscillatory signals are needed in particular. They are usually based on spin-transfer torque, but this study offers an alternative, based on feedback of spin current into a magnetic tunnel junction (MTJ). A combination of thermal fluctuations, magnetoresistance, and the spin Hall effect can induce periodic precessional states in the MTJ's free layer, significantly reducing the critical current for oscillations and improving their quality factor.Keywords:
Spin-transfer torque
Tunnel magnetoresistance
Spin Current
Spin pumping
Spintronic phenomena are made possible via the diffusion of spin-currents or the generation of spin-accumulation. Spinorbitronics uses the electronic spin-orbit coupling (SOC) and emerges as a new route to create spin-currents in the transverse direction of the charge flow. This is made possible via the intrinsic spin Hall conduction (SHE) of heavy metals or extrinsic spin-Hall effect of metallic alloys. SHE borrows its concept from the anomalous Hall effect (AHE) where the relativistic spin-orbit coupling (SOC) promotes an asymmetric deflection of the spin-current. SHE is now at the base of magnetization commutation and domain wall moving via spin-orbit torque (SOT) and spin-transfer torque operations in the FMR regime. However, the exact anatomy of SOT at spin-orbit active interfaces like Co/Pt is still missing. In the case of Pt, recent studies have put forward the major role played by i) the spin-memory loss (SML) and the electronic transparency at 3d/5d interfaces and ii) the inhomogeneity of the conductivity in the current-in-plane (CIP) geometry to explain the discrepancy in the SHE. Ingredients to consider then are the profiles of both the conductivity and spin-current across the multilayers and spin-transmission. In this talk, we will present robust SMR measurements observed on NiCo/Pt multilayer stacks characterized by a perpendicular magnetic anisotropy (PMA). The SMR occurs for both in-plane magnetization rotation or from nominal out-of-plane to the in-plane direction transverse to the current flow. This clearly departs from standard AMR or pure interfacial anisotropic-AMR symmetries. We analyze in large details our SMR signals for the whole series of samples owing to two main guidelines: i) we consider the exact conductivity profile across the multilayers, in particular near the Co/Pt interface, via the Camley-Barnas approach and ii) we derive the spin current profile generated by SHE along the perpendicular direction responsible for SMR. We consider pure interfacial spin dissipation by SML (decoherence, interfacial enhanced scattering) and give out a general analytical expression for SMR. Our conclusions go towards a robust value of the spin-Hall conductivity and SML like previously published. The CIP spin-Hall angle, of the order of 0.10 is larger than the one found in spin-pumping experiments (CPP geometry) owing to the smaller conductivity at the Co/Pt interface, in agreement with the results of STT-FMR experiments.
Spin-transfer torque
Spin diffusion
Spin pumping
Spinplasmonics
Spin valve
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We theoretically investigate the fluctuation of a pure spin current induced by the spin Seebeck effect and spin pumping in a normal-metal--(NM-)ferromagnet(FM) bilayer system. Starting with a simple ferromagnet-insulator--(FI-)NM interface model with both spin-conserving and non-spin-conserving processes, we derive general expressions of the spin current and the spin-current noise at the interface within second-order perturbation of the FI-NM coupling strength, and estimate them for a yttrium-iron-garnet--platinum interface. We show that the spin-current noise can be used to determine the effective spin carried by a magnon modified by the non-spin-conserving process at the interface. In addition, we show that it provides information on the effective spin of a magnon, heating at the interface under spin pumping, and spin Hall angle of the NM.
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Spin Current
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As spintronics continues to replace conventional electronics, devices that produce oscillatory signals are needed in particular. They are usually based on spin-transfer torque, but this study offers an alternative, based on feedback of spin current into a magnetic tunnel junction (MTJ). A combination of thermal fluctuations, magnetoresistance, and the spin Hall effect can induce periodic precessional states in the MTJ's free layer, significantly reducing the critical current for oscillations and improving their quality factor.
Spin-transfer torque
Tunnel magnetoresistance
Spin Current
Spin pumping
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Spin pumping
Spinplasmonics
Spin Current
Spin wave
Spin valve
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A spin battery concept is applied for the dynamical generation of pure spin current and spin transport in p-type silicon (p-Si). Ferromagnetic resonance and effective s-d coupling in Ni80Fe20 results in spin accumulation at the Ni80Fe20/p-Si interface, inducing spin injection and the generation of spin current in the p-Si. The pure spin current is converted to a charge current by the inverse spin Hall effect of Pd evaporated onto the p-Si. This approach demonstrates the generation and transport of pure spin current in p-Si at room temperature.
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Spin Current
Inverse temperature
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This chapter introduces the basic concept of spin current. It begins with an introduction to the general concept of spin and spin current, which is followed by a discussion of particular spin currents, such as incoherent, exchange, topological, and thermal spin currents. The chapter reviews the definition of charge currents for comparison. It talks about a diffusion spin current due to spatial inhomogeneous spin density and a drift spin current in the absence of coherent dynamics of spin. There are some methods for experimentally detecting pure spin currents, spin currents without accompanying charge currents. One direct method is the utilization of the inverse spin-Hall effect, a method which was demonstrated first by spin pumping and nonlocal technique. The chapter explains the exchange interaction in magnets by introducing a concept of an exchange spin current and then formulates a spin-wave spin current.
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Spinplasmonics
Spin wave
Spin diffusion
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Spin Hall effects intermix spin and charge currents even in nonmagnetic materials and, therefore, ultimately may allow the use of spin transport without the need for ferromagnets. We show how spin Hall effects can be quantified by integrating Ni{80}Fe{20}|normal metal (N) bilayers into a coplanar waveguide. A dc spin current in N can be generated by spin pumping in a controllable way by ferromagnetic resonance. The transverse dc voltage detected along the Ni{80}Fe{20}|N has contributions from both the anisotropic magnetoresistance and the spin Hall effect, which can be distinguished by their symmetries. We developed a theory that accounts for both. In this way, we determine the spin Hall angle quantitatively for Pt, Au, and Mo. This approach can readily be adapted to any conducting material with even very small spin Hall angles.
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Spinplasmonics
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Spin current-based electronics, referred to as spintronics, is the promising technology to replace charge current-based technology. Spintronics-based devices allow for the minimization of the size of the device and faster response. The study of spin current efficiency in different materials is one of the emergent research topics in modern days. Spin pumping and inverse spin Hall effect (ISHE) are popular tools for studying the spin current efficiency in materials. In this regard, high spin-orbit coupling (SOC) materials are very useful for such studies. Heavy metals, topological insulators, and Antiferromagnets are used as high SOC layers in this work.
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We overview the recent developments in spin current generation mechanisms and study the spin pumping effect and diffusive spin current in detail based on a microscopic theory. The spin-charge conversion using the inverse spin Hall effect is also discussed. Spin chemical potential describing the diffusive spin current is calculated by linear response theory and spin injection effect is discussed based on the result.
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Spinplasmonics
Spin Current
Spin-transfer torque
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A Spin Current Generated by Spin Pumping in a Ferromagnetic/Nonmagnetic/Spin-Sink Trilayer Film Is Calculated Based on the Spin Pumping Theory and the Standard Spin Diffusion Equation. By Attaching the Spin-Sink Layer, the Injected Spin Current Is Drastically Enhanced when the Interlayer Thickness Is Shorter than the Spin Diffusion Length of the Interlayer. We Also Provided the Formula of the Charge Current which Is Induced from the Pumped Spin Current via the Inverse Spin-Hall Effect.
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Spin diffusion
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