Radboud University Nijmegen PhD thesis, Claudiu Daniel Stanciu Radboud University Nijmegen, The Netherlands ( ) (now working at Océ Technologies)

Radboud University Nijmegen Over 110 years of Magnetic Recording Telegraphone (by Valdemar Poulsen) The first working magnetic recorder (1898) The first hard disk drive – HDD (1955) 5MB memory storage (IBM) The first magnetic tape (1928) Magnetophon (Fritz Pfleumer) The first magnetic core memory (late 1940’s) 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 Hard Disk Drive (HDD) Magnetic Bits Magnetic domains in a HDD - black areas - white areas

Radboud University Nijmegen Challenges in Magnetic Data Storage Higher and higher bit densityHigher and higher data storage speed FASTER switching speed of the tiny magnets SMALLER magnetic areas (tinier magnets) This thesis focuses on the speed of the magnetization switching “By 2012, just two disks will provide the same storage capacity as the human brain!” Robert Birge (Syracuse University) ~ 10 Terabyte FAST!

Radboud University Nijmegen ? How to Switch a Magnet…?

Radboud University Nijmegen Conventional Magnetic Data Storage The conventional way of reversing magnetization is by applying an external magnetic field.

Radboud University Nijmegen Initial state Final state 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?

Radboud University Nijmegen “No matter how short and strong the magnetic-field pulse, magnetic recording cannot be made ever faster than picoseconds.” The Ultimate Speed Limit: a few Picoseconds Magnetic field pulses: 2.3 picoseconds, 3 Tesla 3 km long Stanford Linear Accelerator in California The shortest and strongest magnetic field on the Earth In 2004…

Radboud University Nijmegen New Challenge in Magnetic Data Storage Find novel ways to reverse magnetization to reverse magnetization faster than picoseconds

Radboud University Nijmegen The dream What if light could reverse Magnetization? Opto-MagneticRecording No Magnetic Field! Field! Use Light Pulse: One of the shortest man- made event Unimaginable storage speeds: 100THz and more Light could not only transfer but store the information too Light could not only transfer but store the information too

Radboud University Nijmegen Magnetization changes the polarization of light Spins Photons Controlling magnetization by light Magneto-OpticsOpto-Magnetism ?Opto-magnetism MMMM MMMM  (-)  (+) Inverse Faraday effect Magneto-opticsE E  F ~M z MzMzMzMz Faraday effect

Radboud University Nijmegen 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.” J. Stohr, H. C. Siegmann Magnetism: From Fundamentals to Nanoscale Dynamics, Springer 2006 “… one cannot expect to induce coherent electron spin dynamics in metals with laser pulses of 30 fs duration.”

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! Literature says: Ultrafast opto-magnetic recording is IMPOSSIBLE!

Radboud University Nijmegen …we never say NEVER…

Radboud University Nijmegen Experimental set-up Metallic amorphous alloy GdFeCo typically used in data storage Circularly polarized laser pulses Quarter wave plate Linear polarized laser pulses Magneto-Opticalmicroscope Amplified Ti:Sapphire laser, 1 KHz, 40 fs and 800 nm Before laser excitation GdFeCo thin film Magneto-Optical image

Radboud University Nijmegen Opto-magnetic recording   100  m H ext = 0 Material: GdFeCo, 40 fs pulses at 1kHz C.D. Stanciu et al,, Phys. Rev. Lett. 98, (2007) C.D. Stanciu et al., Phys. Rev. Lett. 99, (2007)

Radboud University Nijmegen 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! With a single 40 fs laser pulse? Opto-magnetic recording

Radboud University Nijmegen Writing time ~ 1 ns Switching Magnets with Magnetic Field ~ 1 GHz Switching Magnets with Light Pulses Writing time ~10 fs ~ 100 THz Traditional Magnetic Recording Ultrafast Opto-Magnetic Recording ~ faster than the actual speed of a Hard Disk Drive

Radboud University Nijmegen 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 to a magnetic material. Radboud University Nijmegen, Nijmegen, The Netherlands: Scientific: Dr. F. Hansteen Dr. A. V. Kimel Dr. A. Kirilyuk Prof. Dr. Th. Rasing Technical: Albert van Etteger Tonnie Nihon University, Tokyo, Japan: Dr. A. Tsukamoto Prof. Dr. A. Seagate Research, USA: Dr. Julius Hohlfeld Dr. Adnan Rebei Financial support: ◦ The European network DYNAMICS ◦ Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) ◦ NanoNed: Nano-Spintronics ◦ Stichting voor Fundamenteel Onderzoek der Materie (FOM) ◦ Grant-in-Aid for Scientific Research of the Ministry of Education, Culture, Sports, Science and Technology in Japan ◦ Seagate Research Thank you for your attention! & Thank you UMICORE and FWO!