Magnetism
✦ first navigational device based on magnetism
✦ made of Copper (nonmagnetic)
✦ magnetite or iron tip on the “spoon”
Magnetism: The early days I
Chinese “south pointer”, ~ 200 B.C.
✦ magnetic interactions lead to mechanical forces and torque
✦ Maxwell’s equations
✦ interplay between electricity and magnetism
Magnetism: The early days II
Military compass by Galileo, ~ A.D. 1600
✦ magnetism as a cooperative phenomenon
✦ long range magnetic order
✦ Heisenberg Hamiltonian
Magnetism & Electronic Structure (1920’s)
✦ Stoner model
✦ Stoner criterion
✦ Density functional theory
✦ Electronic correlations
Magnetism & Electronic Structure (1960)
Fe
✦ Stoner model
✦ Stoner criterion
✦ Density functional theory
✦ Electronic correlations
Magnetism & Electronic Structure (1960)
E
n↓↑( ! k) = E
0( ! k) ± 1
2 I · M
Fe
✦ Stoner model
✦ Stoner criterion
✦ Density functional theory
✦ Electronic correlations
Magnetism & Electronic Structure (1960)
E
n↓↑( ! k) = E
0( ! k) ± 1
2 I · M I · n
0(E
F) > 1
Fe
✦ Stoner model
✦ Stoner criterion
✦ Density functional theory
✦ Electronic correlations
Magnetism & Electronic Structure (1960)
E
n↓↑( ! k) = E
0( ! k) ± 1
2 I · M I · n
0(E
F) > 1
V
X( ! r) = − α e
2! 6 π
"
13# n
↑↓( ! r ) $
13Fe
✦ Stoner model
✦ Stoner criterion
✦ Density functional theory
✦ Electronic correlations
Magnetism & Electronic Structure (1960)
E
n↓↑( ! k) = E
0( ! k) ± 1
2 I · M I · n
0(E
F) > 1
E
XC[n
↑( ! r ), n
↓( ! r)] −→ V
XC↑↓( ! r) V
X( ! r) = − α e
2! 6 π
"
13# n
↑↓( ! r ) $
13Fe
Lecture Part 1&2
•
Magnetism of atoms•
Magnetism in solids 1Magnetism in Solids II
•
exchange interactions in complex materials•
indirect exchange path•
magnetic order intransition metal oxides
Mn
3+O
2-Mn
3+Electronic Correlations
Complex Collective Behavior Novel Ground states
charge ordering orbital ordering spin ordering
Jahn-Teller distortions spin-Peierls transition metal-insulator trans.
Cooper pairs
orbital-/spin-liquid
?
charge spin
lattice orbit External Parameters
magnetic field H electric field E chem. potential µ temperature T
pressure p
strain σ
dimensionality d Novel Functionalities
colossal magnetoresistance high-TC superconductivity neg. thermal expansion
? ccoommppeettiinngg ddeeggrreeeess ooff ffrreeeeddoomm
Electronic Correlations
Complex Collective Behavior Novel Ground states
charge ordering orbital ordering spin ordering
Jahn-Teller distortions spin-Peierls transition metal-insulator trans.
Cooper pairs
orbital-/spin-liquid
?
charge spin
lattice orbit External Parameters
magnetic field H electric field E chem. potential µ temperature T
pressure p
strain σ
dimensionality d Novel Functionalities
colossal magnetoresistance high-TC superconductivity neg. thermal expansion
? ccoommppeettiinngg ddeeggrreeeess ooff ffrreeeeddoomm
Magnetic anisotropy
•
magnetization tends to point along preferred spatial directions•
technologically very important•
related to magnetic ordering temperaturesMagnetism in reduced dimensions
•
2D, 1D, 0D,•
magnetic ordering•
magnetic moments•
anisotropies•
Spin-polarized•
Scanning Tunneling•
MicroscopyProbing Nanomagnetism
Micromagnetic Structures
•
Nonhomogeneous magnetization distribution•
domains, domain walls, etc.•
complex patternsImpact on Technology: 1958 - The RAMAC
IBM 305 RAMAC Random
Access Method of
Accounting and
Control
Impact on Technology: 1958 - The RAMAC
IBM 305 RAMAC Random
Access Method of
Accounting and
Control
Impact on Technology: 1958 - The RAMAC
IBM 305 RAMAC Random
Access Method of
Accounting and
Control
Impact on Technology: 1958 - The RAMAC
IBM 305 RAMAC Random
Access Method of
Accounting and Control
~ 600 kB
Hard disks in the early days
Hard disks in the early days
Hard disks in the early days
(Almost) indestructible
•
Hard disk retrieved from space shuttle ChallengerMagnetic excitations
•
spin waves•
temperature dependenceMagnetodynamics
✦
nonhomogeneous excitation of the magnetization
✦
Landau-Lifshitz-Gilbert equation
✦
micromagnetic simulations
-0.01 0
mz
+0.01
H
pulsex
y 600nm x 200nm x 20nm
M
t=0…1000 ps
static dynamic
-1 0 my
+1
Magnetodynamics
✦
nonhomogeneous excitation of the magnetization
✦
Landau-Lifshitz-Gilbert equation
✦
micromagnetic simulations
-0.01 0
mz
+0.01
H
pulsex
y 600nm x 200nm x 20nm
M
t=0…1000 ps
static dynamic
-1 0 my
+1
Magnetodynamics
✦
nonhomogeneous excitation of the magnetization
✦
Landau-Lifshitz-Gilbert equation
✦
micromagnetic simulations
-0.01 0
mz
+0.01
H
pulsex
y 600nm x 200nm x 20nm
M
t=0…1000 ps
static dynamic
-1 0 my
+1
Magnetodynamics
✦
nonhomogeneous excitation of the magnetization
✦
Landau-Lifshitz-Gilbert equation
✦
micromagnetic simulations
-0.01 0
mz
+0.01
H
pulsex
y 600nm x 200nm x 20nm
M
t=0…1000 ps
static dynamic
-1 0 my
+1
Magnetic coupling phenomena I
•
Interlayer exchange couplingMagnetic coupling phenomena I
•
Interlayer exchange couplingInformation Technology
Information Technology
Spin transport phenomena
•
giant magnetoresistance•
tunneling magnetoresistanceSpin transport: GMR
•
Spin transport: GMR
•
Giant magnetoresistanceSpin transport: GMR
•
∆R/R~1.5%
@
150 mT
Application
?
☺
The MRAM
1kb ring core memory (’65)
vs. 4Mb TMR-based MRAM (’07)
Spin-dependent coupling 2
•
exchange bias•
antiferromagnetsNiO
Fe3O4
Spin transfer and switching
•
spin-polarized current can switch the magnetization•
inversion of GMR or TMR principle•
current-induced dynamicsOptical excitation and switching
•
Can photons switch the magnetization?Time [seconds]
One second Fundamental
physical processes
Electronics Camera
flash
10-15 10-12 10-9 10-6 10-3 100
ps ns
fs µs ms s
Blink of eye
Optical excitation and switching
•
Can photons switch the magnetization?Time [seconds]
One second Fundamental
physical processes
Electronics Camera
flash
10-15 10-12 10-9 10-6 10-3 100
ps ns
fs µs ms s
100 fs = 0.0000000000001 seconds
Ultrashort laser pulse
Blink of eye
✦ smallest solid state magnets
✦ fascinating quantum systems
✦ quantum tunneling of the
Magnetic Molecules
✦ smallest solid state magnets
✦ fascinating quantum systems
✦ quantum tunneling of the magnetization
Magnetic Molecules
✦ smallest solid state magnets
✦ fascinating quantum systems
✦ quantum tunneling of the
