Spin Orbit Torque MRAM Ohio State CEM REU Flashcards

Spin

Intrinsic angular momentum of an electron, typically described as spin-up (+1/2) or spin-down (−1/2)

Spin Polarization

An imbalance between spin-up and spin-down electrons

Spin Current

Flow of spin angular momentum through a material

Charge Current

Flow of electric charge through a material

Spin Hall Effect (SHE)

A charge current generates a transverse spin current due to spin-orbit coupling

Inverse Spin Hall Effect (ISHE)

A spin current generates a transverse charge current or voltage

Spin Accumulation

Build-up of spins at the edges or interfaces of a material

Spin Diffusion Length

Characteristic distance over which spin polarization survives before decaying

Spin Relaxation Time

Average time before electron spins randomize

Momentum Relaxation Time

Average time between electron scattering events

Spin-orbit Coupling

Interaction between an electron’s spin and its motion through a material

Spin Hall Angle

Measure of how efficiently charge current converts into spin current

Spin-transfer Torque

Torque on a magnetic layer caused by spin-polarized current flowing directly through it

Spin-orbit Torque

Torque generated by spin accumulation from spin-orbit effects in an adjacent layer

Torque

A force that causes magnetization to rotate or precess

Magnetization Precession

Rotational motion of magnetization around an effective magnetic field

Ferromagnet

Material with aligned magnetic moments and spontaneous magnetization

Magnetic Anisotropy

Preference of magnetization to point in a certain direction

Perpendicular Magnetic Anisotropy (PMA)

Magnetization prefers pointing out-of-plane

Topological Insulator

Material insulating in the bulk but conductive at the surface with strong spin-orbit effects

Transition Metal Dichalcogenide (TMD)

2D material with formula MX₂ often showing strong spin-orbit coupling.

Berry Phase

Geometric phase accumulated by a quantum state during cyclic evolution

Berry Curvature

Momentum-space quantity acting like an effective magnetic field for electrons

Fermi Velocity

Velocity of electrons near the Fermi level

Drift Velocity

Average electron velocity caused by an electric field

Anomalous Hall Effect

Transverse voltage caused by spin-orbit coupling and magnetization

Hall Voltage

Voltage generated perpendicular to current flow

Spin Pumping

Generation of spin current from a precessing magnet

Spin Mixing Conductance

Measure of spin transfer efficiency across an interface

Gilbert Damping

Dissipation term describing loss of magnetization precession energy

Heavy Metal

Material with strong spin-orbit coupling used for spin current generation

Spin Texture

Spatial arrangement of spin directions in momentum or real space

Cyclic Evolution

Process by which a quantum state accumulates a geometric phase while undergoing periodic changes

Current in x-direction → SHE produces what?

Spin current in y-direction with spins polarized along z

Where does spin accumulate during SHE?

At opposite edges of the sample/channel

Top edge spin direction in SHE?

+z polarization.

Bottom edge spin direction in SHE?

-z polarization.

ISHE geometry

Spin current + spin polarization generate transverse charge current

Transverse response

A current, voltage, or spin accumulation appearing perpendicular to the applied input

Cross product rule in spintronics

Generated response is perpendicular to both current direction and spin direction

DRAM

Dynamic RAM storing charge in capacitors; volatile because charge leaks over time

Volatile memory

Memory requiring power to retain information

Non-volatile memory

Memory retaining information without power

MRAM

Magnetic RAM using magnetic states to store bits

Magnetic tunnel junction (MTJ)

Two magnetic layers separated by a thin insulating barrier

Tunnel magnetoresistance (TMR)

Resistance change depending on relative magnetic alignment of layers

Parallel magnetic alignment

Lower resistance state

Antiparallel magnetic alignment

Higher resistance state

Free layer

Magnetic layer whose magnetization switches

Reference layer

Fixed magnetic layer used for comparison

Spin Hall material

Material used to efficiently generate spin current from charge current

SOT-MRAM

MRAM using spin-orbit torque switching instead of direct current through the MTJ

Radiation hardness

Resistance of electronics to radiation damage

Bi₂Se₃

Topological insulator with strong spin-orbit coupling

Bi₂Te₃

Topological insulator commonly studied for spin transport

WTe₂

TMD with strong spin-orbit effects and broken symmetry

PtTe₂

Transition metal dichalcogenide with strong SOC

TaIrTe₄

Weyl semimetal candidate with strong spin effects

CrTe₂

Magnetic layered material used in spintronics research

Pt (Platinum)

Heavy metal commonly used for SHE experiments

Ta (Tantalum)

Heavy metal often used in SOT devices

MBE (Molecular Beam Epitaxy)

Ultra-high vacuum thin-film growth method using atomic beams

Ultra-high vacuum (UHV)

Extremely low-pressure environment minimizing contamination

Epitaxy

Growth of a crystalline film aligned with the substrate crystal structure

Thin film

Material layer with thickness from atomic scale to microns

Substrate

Base material on which films are grown

Flux (MBE)

Rate at which atoms arrive at the substrate

Effusion cell

Heated source evaporating material during MBE growth

Reflection High-Energy Electron Diffraction (RHEED)

Used for monitoring surface growth in real time

Base pressure

Lowest pressure achieved in a vacuum system

Deposition rate

Speed at which material is deposited onto a substrate

Annealing

Controlled heating to improve crystal quality or interfaces

X-ray diffraction (XRD)

Technique used to determine crystal structure and orientation

Bragg’s Law

Relationship describing constructive interference of x-rays from crystal planes

X-ray reflectivity (XRR)

Technique measuring thin-film thickness and interface quality

Atomic force microscopy (AFM)

Surface imaging technique using a nanoscale probe tip

Scanning electron microscopy (SEM)

Electron imaging technique for surface morphology

Transmission electron microscopy (TEM)

High-resolution imaging through thin samples

Energy dispersive spectroscopy (EDS/EDX)

Elemental analysis using emitted x-rays

Hall measurement

Electrical measurement used to determine carrier density and mobility

Harmonic Hall measurement

Technique for measuring spin-orbit torque strength

SQUID magnetometry

Extremely sensitive magnetization measurement technique

VSM (Vibrating Sample Magnetometry)

Measures magnetic moment using induced voltage

Photolithography

Patterning process using light and photoresist

Photoresist

Light-sensitive material used for lithography

Positive photoresist

Exposed regions become soluble in developer

Negative photoresist

Exposed regions become insoluble

Spin coating

Spreading photoresist uniformly by rapid rotation

Soft bake

Heating step to remove solvent from photoresist

Mask alignment

Aligning photomask pattern with substrate

UV exposure

Exposing resist to ultraviolet light through a mask

Development

Removing soluble regions of photoresist

Hard bake

Post-development bake improving resist durability

Lift-off

Removing resist to leave patterned deposited material behind

Etching

Removing material selectively from exposed regions

Wet etching

Chemical liquid-based material removal

Dry etching

Plasma-based material removal

Ion milling

Physical sputtering process used for etching

Cleanroom

Controlled environment minimizing particles and contamination

Class 100 cleanroom

Fewer than 100 particles (>0.5 μm) per cubic foot of air