Transcript Slide 1

PhD thesis, Claudiu Daniel Stanciu
Radboud University Nijmegen, The Netherlands (2004 - 2008)
(now working at Océ Technologies)
Radboud University Nijmegen
Over 110 years of Magnetic Recording
The first working magnetic recorder (1898)
The first magnetic tape (1928)
Telegraphone (by Valdemar Poulsen)
Magnetophon (Fritz Pfleumer)
The first magnetic core memory (late 1940’s)
The first hard disk drive – HDD (1955)
IBM
5MB memory storage (IBM)
Radboud University Nijmegen
Magnetic Recording Devices Today
The first hard disk drive – HDD (1955)
5MB memory storage (IBM)
Hard disk drive – HDD (2010)
5GB memory storage
Radboud University Nijmegen
Magnetic Data Storage
Magnetic Bits
Hard Disk Drive
(HDD)
0 1
1 0
Magnetic domains in a HDD
- black areas
- white areas
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Challenges in Magnetic Data Storage
Higher and higher bit density
SMALLER magnetic areas
(tinier magnets)
Higher and higher data storage speed
FASTER switching speed
of the tiny magnets
“By 2012, just two disks will provide
the same storage capacity as the human brain!”
FAST!
Robert Birge (Syracuse University)
~ 10 Terabyte
This thesis focuses on the speed of the magnetization switching
Radboud University Nijmegen
How to Switch a Magnet…?
?
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Conventional Magnetic Data Storage
1
1
0
1
1
0
1
0
The conventional way
of reversing magnetization
is by applying an external magnetic field.
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How Fast a Magnet can be Switched…?
Today, the time it takes to switch a magnet in
is ~ 700ps
The speed of this process is proportional with
the strength of the applied magnetic field.
The switching speed
may be as high as desired
provided sufficiently high fields are available!?
~ 700ps
Is there any speed limit?
Initial
state
Final
state
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The Ultimate Speed Limit: a few Picoseconds
In 2004…
3 km long Stanford
Linear Accelerator in California
The shortest and strongest magnetic
field on the Earth
Magnetic field pulses:
2.3 picoseconds, 3 Tesla
“No matter how short and strong the magnetic-field pulse,
magnetic recording cannot be made ever faster than picoseconds.”
Radboud University Nijmegen
New Challenge in Magnetic Data Storage
Find novel ways
to reverse magnetization
faster than picoseconds
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The dream
Use Light Pulse:
No Magnetic
What
if light could reverse Magnetization?
One of the
Field!
shortest manmade event
Light could not only
transfer but store
the information too
Opto-Magnetic
Recording
Unimaginable
storage speeds:
100THz and
more
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Opto-Magnetism
Magneto-Optics
Magnetization
Controlling
changes
magnetization
the polarization
by lightof light
Magneto-optics
Opto-magnetism
qF ~Mz
E
E
Mz
Faraday effect
Spins
s(-)
s(+)
dM
?
dM
Inverse Faraday effect
Photons
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Is all-optical magnetization reversal feasible?
“The amount of the photons involved in the experiments
is far not enough to contribute a significant angular momentum.”
“In metals, electron-electron scattering appears to make coherent
manipulation of magnetization difficult if not impossible.”
“… one cannot expect to induce coherent electron spin
dynamics in metals with laser pulses of 30 fs duration.”
J. Stohr, H. C. Siegmann
Magnetism: From Fundamentals to Nanoscale Dynamics, Springer 2006
Radboud University Nijmegen
Ultrafast opto-magnetic recording…?
Speed limit?
Not enough photons?
Electron-electron scattering a problem?
Literature says:
Ultrafast opto-magnetic recording is IMPOSSIBLE!
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…we never say NEVER…
Radboud University Nijmegen
Experimental set-up
Amplified Ti:Sapphire laser, 1 KHz, 40 fs and 800 nm
Magneto-Optical image
Linear polarized
laser pulses
GdFeCo thin film
Quarter wave
plate
Circularly polarized
laser pulses
Metallic amorphous alloy
GdFeCo
typically used in
data storage
Before laser
excitation
Magneto-Optical
microscope
Radboud University Nijmegen
Opto-magnetic recording
40 fs pulses at 1kHz
Material: GdFeCo, Hext = 0
s+
s-
100mm
C.D. Stanciu et al,, Phys. Rev. Lett. 98, 207401 (2007)
C.D. Stanciu et al., Phys. Rev. Lett. 99, 047601 (2007)
Radboud University Nijmegen
Opto-magnetic recording
With a single 40 fs laser pulse?
Sweeping the pulsed laser beam at high speed across the sample
Each domain is written with a single 40 fs laser pulse
Braking the speed limit of magnetic recording with an
effect previously believed impossible!
Radboud University Nijmegen
Ultrafast
Traditional
Opto-Magnetic
Magnetic Recording
Recording
Switching
Switching
Magnets
Magnets
with
with
Magnetic
Light Pulses
Field
Writing time ~10
~ 1 ns
~ ~100
1 GHz
THz
fs
~50.000 faster
than the actual speed
of a Hard Disk Drive
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Femtosecond is one quadrillionth of a second,
and 40 femtoseconds
is all it takes for a bit of data to be written
to a magnetic material.
Thank you for your attention!
&
Thank you
UMICORE and FWO!
Radboud University Nijmegen