Query: Current-induced torques in magnetic materials

Candidate papers:

abstract: The magnetization of a magnetic material can be reversed by using electric currents that transport spin angular momentum. In the reciprocal process a changing magnetization orientation produces currents that transport spin angular momentum. Understanding how these processes occur reveals the intricate connection between magnetization and spin transport, and can transform technologies that generate, store or process information via the magnetization direction. Here we explain how currents can generate torques that affect the magnetic orientation and the reciprocal effect in a wide variety of magnetic materials and structures. We also discuss recent state of the art demonstrations of current induced torque devices that show great promise for enhancing the functionality of semiconductor devices.
author_names: Arne Brataas

Andrew D Kent

Hideo Ohno
title: Current induced torques in magnetic materials.
venue: Nature materials
year: 2012

author_names: Arne Brataas

Andrew D Kent

Hideo Ohno
title: Current Induced Torques in Magnetic Materials
year: 2012

abstract: Spin orbit coupling in inversion asymmetric magnetic crystals and structures has emerged as a powerful tool to generate complex magnetic textures, interconvert charge and spin under applied current, and control magnetization dynamics. Current induced spin orbit torques mediate the transfer of angular momentum from the lattice to the spin system, leading to sustained magnetic oscillations or switching of ferromagnetic as well as antiferromagnetic structures. The manipulation of magnetic order, domain walls and skyrmions by spin orbit torques provides evidence of the microscopic interactions between charge and spin in a variety of materials and opens novel strategies to design spintronic devices with potentially high impact in data storage, nonvolatile logic, and magnonic applications. This paper reviews recent progress in the field of spin orbitronics, focusing on theoretical models, material properties, and experimental results obtained on bulk noncentrosymmetric conductors and multilayer heterostructures, including metals, semiconductors, and topological insulator systems. Relevant aspects for improving the understanding and optimizing the efficiency of nonequilibrium spin orbit phenomena in future nanoscale devices are also discussed.
author_names: Aurelien Manchon

Ioan Mihai Miron

Tomas Jungwirth

Jairo Sinova

J Zelezn'y

Andr'e Thiaville

Kevin Garello

Pietro Gambardella
title: Current induced spin orbit torques in ferromagnetic and antiferromagnetic systems
venue: Reviews of Modern Physics
year: 2019

abstract: Spintronics exploit spin orbit coupling (SOC) to generate spin currents, spin torques, and, in the absence of inversion symmetry, Rashba and Dzyaloshinskii Moriya interactions. The widely used magnetic materials, based on 3d metals such as Fe and Co, possess a small SOC. To circumvent this shortcoming, the common practice has been to utilize the large SOC of nonmagnetic layers of 5d heavy metals (HMs) such as Pt, to generate spin currents and, in turn, exert spin torques on the magnetic layers. Here, a new class of material architectures is introduced, excluding nonmagnetic 5d HMs, for high performance spintronics operations. Very strong current induced torques exerted on single ferrimagnetic GdFeCo layers, due to the combination of large SOC of the Gd 5d states and inversion symmetry breaking mainly engineered by interfaces, are demonstrated. These "self torques" are enhanced around the magnetization compensation temperature and can be tuned by adjusting the spin absorption outside the GdFeCo layer. In other measurements, the very large emission of spin current from GdFeCo, 80% (20% of spin anomalous Hall effect (spin Hall effect) symmetry is determined. This material platform opens new perspectives to exert "self torques" on single magnetic layers as well as to generate spin currents from a magnetic layer.
author_names: David C'espedes-Berrocal

Heloise Damas

Sebastien Petit-Watelot

Davide Maccariello

Ping Tang

Aldo Arriola-C'ordova

Pierre Vallobra

Yong Xu

Jean-Lois Bello

Elodie Martin

Sylvie Migot

Jaafar Ghanbaja

Shufeng Zhang

Michel Hehn

Stephane Mangin

Christos Panagopoulos

Vincent Cros

Albert Fert

Juan-Carlos Rojas-Sanchez
title: Current Induced Spin Torques on Single GdFeCo Magnetic Layers.
venue: Advanced materials
year: 2021

abstract: In this review article, an insight of the physics that explains the phenomenon of torques induced by currents in systems comprising ferromagnetic (FM) non magnetic (NM) materials has been provided with particular emphasis on experiments that concern the observation of such torques. An important requirement of systems that enables observation of such relativistic torques is that the material needs to possess large spin orbit coupling (SOC) In addition, the FM/NM interface should be of high quality so that spin angular momentum can be transferred across the interface. Under such conditions, the magnetization of a magnetic material experiences a torque, and can be reversed, thanks to the phenomenon of the spin Hall effect in the NM layer with large SOC. A reciprocal process also occurs, in which a changing magnetization orientation can produce spin current, i.e. current that supports spin angular momentum. It is important to know how these processes occur which often tells us about the close connection between magnetization and spin transport. This paves the way to transform technologies that process information via magnetization direction, namely in magnetic recording industry. This field of physics being relatively young much remains to be understood and explored. Through this review we have attempted to provide a glimpse of existing understanding of current induced torques in ferromagnetic thin film heterostructures along with some future challenges and opportunities of this evolving area of spintronics. Specifically, we have discussed the state of the art demonstrations of current induced torque devices that show great promise for enhancing the functionality of magnetic memory devices.
author_names: Bhaskar Kaviraj

Jaivardhan Sinha
title: Relativistic torques induced by currents in magnetic materials: physics and experiments
year: 2018

abstract: There exists a significant challenge in developing efficient magnetic tunnel junctions with low write currents for non volatile memory devices. With the aim of analysing potential materials for efficient current operated magnetic junctions we have developed a multi scale methodology combining the ab initio calculations of spin transfer torque with large scale time dependent simulations using atomistic spin dynamics. In this work we introduce our multi scale approach including a discussion on a number of possible mapping schemes the ab initio spin torques into the spin dynamics. We demonstrate this methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin torques are primarily acting at the interface between the Co free layer and MgO. Using spin dynamics we then calculate the reversal switching times for the free layer and the critical voltages and currents required for such switching. Our work provides an efficient, accurate and versatile framework for designing novel current operated magnetic devices, where all the materials details are take into account.
author_names: Matthew O A Ellis

Maria Stamenova

Stefano Sanvito
title: Multiscale modeling of current induced switching in magnetic tunnel junctions using ab initio spin transfer torques
year: 2017

abstract: Control of magnetization in magnetic nanostructures is essential for development of spintronic devices because it governs fundamental device characteristics such as energy consumption, areal density, and operation speed. In this respect, spin orbit torque (SOT) which originates from the spin orbit interaction, has been widely investigated due to its efficient manipulation of the magnetization using in plane current. SOT spearheads novel spintronic applications including high speed magnetic memories, reconfigurable logics, and neuromorphic computing. Herein, recent advances in SOT research, highlighting the considerable benefits and challenges of SOT based spintronic devices, are reviewed. First, the materials and structural engineering that enhances SOT efficiency are discussed. Then major experimental results for field free SOT switching of perpendicular magnetization are summarized, which includes the introduction of an internal effective magnetic field and the generation of a distinct spin current with out of plane spin polarization. Finally, advanced SOT functionalities are presented, focusing on the demonstration of reconfigurable and complementary operation in spin logic devices.
author_names: Jeongchun Ryu

Soogil Lee

Kyung-Jin Lee

Byong-Guk Park
title: Current Induced Spin Orbit Torques for Spintronic Applications.
venue: Advanced materials
year: 2020

abstract: We report on the switching of the in plane magnetization of thin yttrium iron garnet (YIG)/Pt bilayers induced by an electrical current. The switching is either field induced and assisted by a dc current, or current induced and assisted by a static magnetic field. The reversal of magnetization occurs at a current density as low as 105 A/cm2 and magnetic fields of ~40 mT, two orders of magnitude smaller than in ferromagnetic metals, and consistent with the weak uniaxial anisotropy of the YIG layers. We use the transverse component of the spin Hall magnetoresistance to sense the magnetic orientation of YIG while sweeping the current. Our measurements and simulations reveal that the current induced effective field responsible for switching is due to the Oersted field generated by the current flowing in the Pt layer rather than by spin orbit torques, and that the switching efficiency is influenced by pinning of the magnetic domains.
author_names: Johannes Mendil

Morgan Trassin

Quingquing Bu

Manfred Fiebig

Pietro Gambardella

Department of Materials

Eth Zurich

8093 Zurich
title: Current induced switching of YIG/Pt bilayers with in plane magnetization due to Oersted fields
venue: Applied Physics Letters
year: 2019

abstract: We have studied the effects of electrical current pulses on skyrmion nucleation in a series of Pt/Co/Ni based multilayers. Transmission X ray microscopy reveals that by applying electrical current pulses of duration and current density on the order of \tau$=50 \mu$s and j=10$^9$ ^1$^0$ A/m$^2$ respectively, in an applied magnetic field of \mu$$_0$Hz=50 mT, stripe to skyrmion transformations are attained. The skyrmions remain stable across a wide range of magnetic fields, including zero field. We primarily attribute the transition to current induced Joule heating, with the minor contribution of spin orbit torques. Reducing the magnetic moment and perpendicular anisotropy using rare earth spacers lowers the current and magnetic field needed to accomplish the transition. These findings support the idea that energetic inputs allow for the formation and stabilization of skyrmions in a broader class of materials than previously thought possible, and that material properties can be tuned to yield a more energy efficient stabilization of the skyrmion phase.
author_names: J A Brock

S A Montoya

Mi-Young Im

Eric E Fullerton
title: Energy efficient current induced skyrmion phases in Co/Ni/Pt based multilayers
year: 2020

abstract: In magnets without inversion symmetry weak spin orbit coupling leads to the formation of smooth twisted magnetic structures like helices with a long period. In 2009, a new chiral magnetic phase was observed in the helimagnet manganese silicide (MnSi) within a certain temperature and magnetic field range. It turned out that this phase is a lattice of skyrmions which are topologically stable whirl lines. In the first Part of this Thesis, we review the discovery of the skyrmion lattice in MnSi, its manifestation in other chiral magnets and in thin films. Furthermore, we review the Ginzburg Landau theory for chiral magnetic structures describing their equilibrium properties, followed by a discussion of additional terms that orient and distort the skyrmion lattice. Finally, we analyze the crystalline nature of the skyrmion lattice. In the second Part of this Thesis, we investigate the interplay of electric currents and magnetic structures in bulk materials, in particular the skyrmion phase. Electrons traversing a spatially or temporally inhomogeneous magnetization configuration pick up a Berry phase which, rewritten as an Aharonov Bohm phase arising from emergent magnetic and electric fields, leads to an effective Lorentz force acting on the electrons. For the skyrmion lattice these emergent fields are particularly interesting as the emergent magnetic field is quantized due to the topology of the skyrmions. On the other hand, the electric current induces forces on the magnetic texture via spin tranfer torques, describing the transfer of angular momentum from the conduction electrons to the local magnetic structure. We show that skyrmions act very sensitively to electric currents, and we study their current induced dynamics, i.e. the translational motion as well as rotations of the topologically stable knots. This research was, is and will be done in cooperation with recent experiments performed by the group of Prof. Dr. Christian Pfleiderer from the Technical University of Munich. The very efficient coupling of skyrmions to electric currents was experimentally confirmed by an ultra low threshold current density of about 10^6 A/m^2 above which spin transfer torque effects were observed. It is about five order of magnitude smaller compared to that of other present day spin torque effects like domain wall motion. Hence, skyrmions are expected to be excellent systems to study the interplay of magnetism and electric currents, thereby advancing the general understanding of spin transfer torque effects. We further think that the gained knowledge from such studies might be useful for future spintronic devices.
author_names: Karin Everschor
title: Current Induced Dynamics of Chiral Magnetic Structures Skyrmions, Emergent Electrodynamics and Spin Transfer Torques
year: 2012