Transcript Slide 1

Spintronics
Tomas Jungwirth
Institute of Physics ASCR, Prague
University of Nottingham
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
Hard disk drive
First hard disc (1956) - classical electromagnet for read-out
1 bit: 1mm x 1mm
MB’s
From PC hard drives ('90)
to micro-discs - spintronic read-heads
1 bit: 10-3mm x 10-3mm
10’s-100’s GB’s
Dawn of spintronics
Magnetoresistive read element
Inductive read/write element
Anisotropic magnetoresistance (AMR) – 1850’s  1990’s
Giant magnetoresistance (GMR) – 1988  1997
MRAM – universal memory
fast, small, low-power, durable, and non-volatile
2006- First commercial 4Mb MRAM
Based on Tunneling Magneto-Resistance (similar to GMR but insulating spacer)
RAM chip that actually won't forget  instant on-and-off computers
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
Spin-orbit coupling from classical E&M and postulated electron spin
nucleus rest frame
electron rest frame
I  Qv
1
B   0 0 v  E  2 v  E
c
H SO
E
Q
4 0 r
3
r
0 I  r
B
4 r 3
g B
e

SB 
SvE
2
2
2mc
Lorentz transformation  Thomas precession
e… it’s all about spin and charge
of electron communicating
SO coupling from relativistic QM
quantum mechanics & special relativity  Dirac equation
E=p2/2m
E2/c2=p2+m2c2
E ih d/dt
Spin
(E=mc2 for p=0)
p -ih d/dr
Anisotropic Magneto-Resistance
& HSO (2nd order in v/c around
the non-relativistic limit)
~ 1% MR effect
Current sensitive to magnetization direction
Ferromagnetism = Pauli exclusion principle & Coulomb repulsion
etotal wf antisymmetric
e-
= orbital wf antisymmetric * spin wf symmetric
(aligned)
DOS
e-
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)
DOS
Giant Magneto-Resistance
>
P AP
  
~ 10% MR effect
Tunneling Magneto-Resistance
DOS  DOS
~ 100% MR effect
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
Tunneling Anisotropic Magneto-Resistance
TMR
Au
Au
Discovered in ferromagnetic semiconductors (Tc < room T)
Ga
Mn
As
First successful attempts in metals
Mn
Magneto-Resistive transistors
Spin Transfer Torque writing
Magnetic domain “race-track” memory
Spintronics in nominally non-magnetic materials
Datta-Das transistor
Spin Hall effect
spin-dependent deflection  transverse edge spin polarization
skew scattering
intrinsic
_
__
side jump
FSO
FSO
I
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
p
n
n
SHE mikročip, 100A
SHE detected elecrically in metals
Cu
supercondicting magnet, 100 A
SHE edge spin accumulation can be
extracted and moved further into the circuit
Magnetization
Spintronics explores new avenues for:
• Information reading


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
Ga
As
• New materials
Ferromagnetic semiconductors
Non-magnetic SO-coupled systems
Mn
Mn