Spintronics

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Spintronics
Tomas Jungwirth
University of Nottingham
Institute of Physics ASCR, Prague
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1. Current spintronics in HDD read-heads and
MRAMs 2. Basic physical principles of the
operation of current spintronic devices
3. Spintronics research 4. Summary
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Hard disk drive
First hard disc (1956) - classical electromagnet
for read-out
1 bit 1mm x 1mm
MBs
From PC hard drives ('90) to micro-discs -
spintronic read-heads
1 bit 10-3mm x 10-3mm
10s-100s GBs
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Dawn of spintronics
Magnetoresistive read element
Inductive read/write element
Anisotropic magnetoresistance (AMR) 1850s ?
1990s Giant magnetoresistance (GMR) 1988 ?
1997
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MRAM universal memory fast, small, low-power,
durable, and non-volatile
2006- First commercial 4Mb MRAM
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Based on Tunneling Magneto-Resistance (similar to
GMR but insulating spacer)
RAM chip that actually won't forget ? instant
on-and-off computers
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1. Current spintronics in HDD read-heads and
MRAMs 2. Basic physical principles of the
operation of current spintronic devices
3. Spintronics research 4. Summary
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Spin-orbit coupling from classical EM and
postulated electron spin
nucleus rest frame
electron rest frame
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Lorentz transformation ? Thomas precession
its all about spin and charge of electron
communicating
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SO coupling from relativistic QM
quantum mechanics special relativity ? Dirac
equation


Ep2/2m E? ih d/dt p? -ih d/dr
E2/c2p2m2c2 (Emc2 for p0)
Spin
HSO (2nd order in v/c around the
non-relativistic limit)
Anisotropic Magneto-Resistance
1 MR effect
Current sensitive to magnetization direction
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Ferromagnetism Pauli exclusion principle
Coulomb repulsion
DOS
DOS

• Robust (can be as strong as bonding in solids)
• Strong coupling to magnetic field
• (weak fields anisotropy fields needed
• only to reorient macroscopic moment)

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DOS
?? ? ??
Giant Magneto-Resistance
?AP
gt
?P
10 MR effect
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Tunneling Magneto-Resistance
DOS? ? DOS?
100 MR effect
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1. Current spintronics in HDD read-heads and
MRAMs 2. Basic physical principles of the
operation of current spintronic devices
3. Spintronics research 4. Summary
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Tunneling Anisotropic Magneto-Resistance
TMR
Au
Au
Discovered in ferromagnetic semiconductors (Tc lt
room T) First successful attempts in metals
Magneto-Resistive transistors
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Spin Transfer Torque writing
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Magnetic domain race-track memory
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Spintronics in nominally non-magnetic materials
Datta-Das transistor
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Spin Hall effect spin-dependent deflection ?
transverse edge spin polarization
skew scattering
side jump
intrinsic
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Spin Hall effect detected optically in
GaAs-based structures
Same magnetization achieved by external field
generated by a superconducting magnet with 106 x
larger dimensions 106 x larger currents
SHE mikrocip, 100?A
supercondicting magnet, 100 A
SHE edge spin accumulation can be extracted and
moved further into the circuit
SHE detected elecrically in metals
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Spintronics explores new avenues for
?

• Information reading

• 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 materials

Ferromagnetic semiconductors Non-magnetic
SO-coupled systems