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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: