Magnetic data writing by using light
Researchers of the Institute for Molecules and Materials (IMM) at the Radboud University in Nijmegen, The Netherlands, together with a Japanese scientific team, have shown that the polarity of a magnet can be reversed by means of a very short pulse. This technology is even about one hundred thousand times faster than is feasible by using the conventional magnetic techniques. The researchers have applied for a patent to this discovery. This finding will be published in the renowned scientific journal Physical Review Letters on 27 July 2007.
If you want to reverse the polarity of a magnet - that is, to change north and south - then usually a strong magnet is brought close to it. Exactly the same happens with a hard disk of a computer, in which the bits (1 and 0 of the binary code) are being written to the disk in small magnetic domains. Today this is possible within a few nanoseconds (one nanosecond is one thousand millionth of a second). This might be fast - and it is amazingly fast in comparison with computers dating from half a century ago - but further improvements are not possible when using the current technology. Also from a fundamental point of view this seemed to be the most feasible. However, the researchers at the Radboud University Nijmegen have discovered quite a different method that easily exceeds the current speed limit. They accomplished to reverse polarity by using a so-called circular polarized pulse that just lasts for 40 femtoseconds. This is about a hundred thousand times faster than the current limit in reversing magnetic polarity (one femtosecond is one millionth of one thousand millionth second). Only recently, scientific literature has asserted that this idea was out of the question, but Alexey Kimel - one of the researchers - stated 'never say never'.
Using laser light to operate magnets
A hard disk contains about two trillion small magnets. In order to transfer data, these magnets have to transmit very quickly. The transmission is caused by an electromagnet. If the electric power is switched on, then a magnetic field is being generated and the magnet transmits to 180 degrees. The faster the electric power is switched on or off, the faster the computer will operate. However, there is a limitation on the transmission speed of electric power, which is a few nanoseconds per transmission at top speed.
All over the world scientists jumped on the researchers at the Radboud University Nijmegen when they suggested that even a laser might be used for reversing polarity. One scientist wrote that magnets just cannot be influenced by light; another one remarked that laser light is not powerful enough. Even last year a book on magnetism was published, in which the idea was disposed of as being completely impossible. In theory, not that unusual: the current theories, based on thermodynamics, do not explain these spectacular research findings either. However, the researchers at the Radboud University do not restrain themselves from anything, and they are already busy to level the next barrier: how can ultra-fast reversion be applied to nanomagnets, that is, magnets that are ten to one hundred times smaller than de wavelength of the light that is used. The fields (domains) that are covered by the current laser pulses, have a diameter of about five micrometer (one micrometer is one thousandth millimeter), which is much larger than in the existing systems. This drawback might be overcome by using nanomagnets. Therefore, the researchers are collaborating with a scientific team in Switzerland.
The research at the Radboud University Nijmegen in The Netherlands has been financed jointly by EU-RTN network ‘Dynamics’, the NanoNed programme and NWO (Netherlands Organisation for Scientific Research); (a Vidi grant of the Division Physics to Alexey Kimel)).
References:
Daniel Stanciu, Fredrik Hansteen, Alexey Kimel, Andrei Kirilyuk, Arata Tsukamoto, Akivoshi Itoh and Theo Rasing, 'All-optical magnetic recording with circularly polarized light', Physical Review Letters, publishing date 26 July 2007.
For further information, please contact Professor Theo Rasing, phone (024) 365 31 02 or Alexey Kimel, phone (024) 365 30 26.