Spintronics Spintronics

Tomas Jungwirth

University of Nottingham

Institute of Physics ASCR, Prague

1.1. Current Current sspipintronics in HDD read-heads and MRAMsntronics in HDD read-heads and MRAMs

2.2. Basic Basic physical principles of the operation of current spintronic physical principles of the operation of current spintronic devices devices

3.3. S Spintronipintronics researchcs research

4. Summary4. Summary

Hard disk drive Hard disk drive

First hard discFirst hard disc (1956) (1956) - - classical electromagnet for read-outclassical electromagnet for read-out

From PC hard drives ('90)From PC hard drives ('90)to mto miicro-discscro-discs - - spintronispintronic read-headsc read-heads

MBMB’s’s

10’s-100’s 10’s-100’s GBGB’s’s

1 bit: 1mm x 1mm1 bit: 1mm x 1mm

1 bit: 101 bit: 10-3-3mm x 10mm x 10-3-3mmmm

Dawn of spintronicsDawn of spintronics

Anisotropic magnetoresistance (AMR) – 1850’s Anisotropic magnetoresistance (AMR) – 1850’s 1990’s 1990’s

Giant magnetoresistance (GMR) – 1988 Giant magnetoresistance (GMR) – 1988 1997 1997

Inductive read/write element

Magnetoresistive read element

MRAM – universal memoryMRAM – universal memory fast, small, low-power, durable, and non-volatile

2006- First commercial 4Mb MRAM

RAM chip that actually won't forget instant on-and-off computers

Based on Tunneling Magneto-Resistance (similar to GMR but insulating spacer)

1.1. Current Current sspipintronics in HDD read-heads and MRAMsntronics in HDD read-heads and MRAMs

2.2. Basic Basic physical principles of the operation of current spintronic physical principles of the operation of current spintronic devices devices

3.3. S Spintronipintronics researchcs research

4. Summary4. Summary

Spin-orbit coupling from classical E&M and postulated electron spin Spin-orbit coupling from classical E&M and postulated electron spin

nucleus rest frame electron rest frame

vI Q rE3

04 r

Q

3

0

4 r

rIB

EvEvB 200

1

c EvSS

2B

mc

egH B

SO

Lorentz transformation Thomas precession

2 2

ee--

… it’s all about spin and chargeof electron communicating

quantum mechanics & special relativity Dirac equation

E=p2/2mE ih d/dtp -ih d/dr

E2/c2=p2+m2c2

(E=mc2 for p=0)

& HSO (2nd order in v/c around the non-relativistic limit)

Spin

Anisotropic Magneto-ResistanceAnisotropic Magneto-Resistance

Current sensitive to magnetization direction

~ 1% MR effect~ 1% MR effect

SO coupling from relativistic QM SO coupling from relativistic QM

FerromagnetismFerromagnetism = Pauli exclusion principle & Coulomb repulsion = Pauli exclusion principle & Coulomb repulsion

total wf antisymmetric = orbital wf antisymmetric * spin wf symmetric (aligned)

• RobustRobust (can be as strong as bonding in solids)(can be as strong as bonding in solids)

• Strong coupling to magnetic fieldStrong coupling to magnetic field (weak fields = anisotropy fields needed (weak fields = anisotropy fields needed only to reorient macroscopic moment)only to reorient macroscopic moment)

DOS

DOS

ee--

ee--

ee--

Giant Magneto-ResistanceGiant Magneto-Resistance

~ 10% MR effect~ 10% MR effect

DOS

AP

P

>

Tunneling Magneto-ResistanceTunneling Magneto-Resistance

~ 100% MR effect~ 100% MR effect

DOS DOS

1.1. Current Current sspipintronics in HDD read-heads and MRAMsntronics in HDD read-heads and MRAMs

2.2. Basic Basic physical principles of the operation of current spintronic physical principles of the operation of current spintronic devices devices

3.3. S Spintronipintronics researchcs research

4. Summary4. Summary

TMRTMRTunneling Anisotropic Magneto-ResistanceTunneling Anisotropic Magneto-Resistance

Magneto-Resistive transistorsMagneto-Resistive transistors

Discovered in ferromagnetic semiconductors (Tc < room T)

First successful attempts in metals

Mn

GaAs Mn

Au

Au

Spin Transfer Torque writingSpin Transfer Torque writing

Magnetic domain “race-track” memoryMagnetic domain “race-track” memory

Datta-Das transistor

Spintronics in nominally non-magnetic materialsSpintronics in nominally non-magnetic materials

intrinsic skew scattering side jump

I

_ FSO

FSO

_ __

Spin Hall effectspin-dependent deflection transverse edge spin polarization

n

n

p

SHE mikročip, 100A supercondicting magnet, 100 A

Spin Hall effect detected optically in GaAs-based structures

Same magnetization achievedby external field generated bya superconducting magnet with 106 x larger dimensions & 106 x larger currents

Cu

SHE detected elecrically in metals SHE edge spin accumulation can beextracted and moved further into the circuit

• Information reading

Ferro

Magnetization

Current

• Information reading & storage

Tunneling magneto-resistance sensor and memory bit

• Information reading & storage & writing

Current induced magnetization switching

• Information reading & storage & writing & processing

Spintronic transistor::magnetoresistance controlled by gate voltage

• New materialsFerromagnetic semiconductorsNon-magnetic SO-coupled systems

Mn

GaAs Mn

Spintronics explores new avenues for: