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Physics and applications ofPhysics and applications of spintronicsspintronics

Tomas Jungwirth

University of NottinghamInstitute of Physics ASCR, Prague

University of Cambridge & Hitachi Cambridge Lab

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Information reading

Information reading & storage

MRAM chips

Information reading & storage & writing

magnetization switching by spin-currents

Information reading & storage & writing & processingspins & transistors & semiconductors

Mn

Ga

As Mn

Spintronics explores new avenues for

GMR, TMR sensors

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quantum mechanics & special relativity

Spin from relativistic quantum mechanicsSpin from relativistic quantum mechanics

Dirac equation electron has charge and internal angular momentum

internal magnetic moment = spin

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SpintronicsSpintronics

its all about spin and charge of electroncommunicating with each other

ee-- ss

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FerromagnetismFerromagnetism == PauliPauli exclusion principle & Coulomb repulsionexclusion principle & Coulomb repulsion

DOS

DOS

ee--

ee--

ee--

Collective spin behavior easy to manipulate spins large sensitivity (magnetic fields)

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SpinSpin--orbit couplingorbit coupling

nucleus rest frame electron rest frame

EvSBS == 222 mc

eg

HB

SOh

ee--

Magnetic anisotropy bistability & hysteresis magnetic memory

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Simplicity of translation fromphysics to electronics

Resistor

Tunneling device

Electro-chemical potential

Density of states

Scattering lifetimes

Complexity of designEfficiency ofEfficiency of

spintronicspintronic devicesdevices

Single Electron Transistor

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~ 100% MR effect~ 100% MR effect

DOS < DOS

SpinSpin--dependent DOSdependent DOS tunnelingtunneling magnetoresistancemagnetoresistance

DOS < DOS

DOS < DOS

DOS > DOS >

HDD read-head sensors

Non-volatile magnetic RAM

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M

[110]

[100]

[110] [010]

SpinSpin--dependent electrodependent electro--chemical potentialchemical potential

M

M

~1000% MR controlled by low-gate-voltage

spintronicspintronic transistortransistor for amplification and logic

Source Drain

Gate

VG

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WhyWhy spintronicspintronic transistors?transistors?

IntergratingIntergrating conventionalconventional spintronicspintronic and electronic devices in one physical elementand electronic devices in one physical elemente.g. TMR magnetic tunnel junctions with transistorse.g. TMR magnetic tunnel junctions with transistors

Pure electrical control (no external magnetic fields) ofPure electrical control (no external magnetic fields) of spintronicsspintronics

e.g. magnetization switching induced by gate voltage on ae.g. magnetization switching induced by gate voltage on a spintronicspintronic transistortransistor

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Mn

Ga

As

Mn

Other approach: make conventional SC magneticOther approach: make conventional SC magnetic

GaAsGaAs -- standard IIIstandard III--V semiconductorV semiconductor

GroupGroup--IIII MnMn -- dilutedilute magneticmagnetic momentsmoments

& holes& holes

GaAsGaAs::MnMn -- feferrromagneticromagnetic & electrically& electricallydoped semiconductordoped semiconductor

More tricky than just hammering an iron nail in a silicon wafer

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Non-volatile gating of GaAs:Mn by ferroelectric gate

superhybrid ferromagnetic/ferroelectric/semiconducting FET

Electrical gate control of ultra-thin Fe on Au

large change of magnetic anisotropy byelectric fields in room-temperature FM

Proximity effects in FS/FM hybrids

magnetic behavior of a GaAs:Mninterfacial layer at room-temperature

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I || E

_ FSO

FSO

_ __

Spin Hall effect

spin-dependent deflection transverse edge spin polarization

E

+v

-v

+S

-S

EvS =2

mc

eHSO

SpintronicsSpintronics in nonin non--magnetic materialsmagnetic materials

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spin Hall effect mikro-chip

Same magnetization in a normal semiconductor achieved at106 x smaller dimensions & 106 x smaller currents

superconducting magnet

The potential ofThe potential of spintronicsspintronics ..

need to learn much more to fully exploit spin in microelectronneed to learn much more to fully exploit spin in microelectronicsics

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