PSI scientists Loïc Le
Guyader (left) and Souliman
El Moussaoui adjusting the
laser that was used to heat
the magnetic sample; © PSI
They have demonstrated that the positions of both North and the South poles of a magnet can be inverted by an ultra short very intense heat pulse created by a short laser flash. This heat pulse brings the magnet into a strongly non-equilibrium state (the bit is neither “0” nor “1”) from where it will relax to the “0” or “1”-state within several picoseconds (1 picosecond = 0.000 000 000 001 second).
This method of recording might allow one to record Terabytes (1000s of Gigabytes) of information per second being 100s of times faster than present hard drive technology, and consumes much less energy by using heat without the need for a magnetic field. The scientists working on this project come from the United Kingdom, Spain, Switzerland, Ukraine, Russia, Japan and the Netherlands. Using modern lithographic methods and x-ray microscopy, researchers from the Paul Scherrer Institute contributed considerably to this work.
Everyone who has experienced the attractive and repulsive forces of magnets knows that there is a North and a South pole and that the North pole of one magnet is attracted to the South pole of another and two like poles repel each other. Such magnets, but much smaller than those known from our everyday life are employed in modern magnetic recording technology, e.g. in hard disk drives. This technology uses the polarity of nanometre size magnets to represent bits of information (“0”and “1”). Until now it was believed that in order to record one bit of information, that is invert the poles of a magnet, it was necessary to apply an external magnetic field. For example, modern hard drives record magnetic bits by applying magnetic fields with a strength of up to 1 Tesla (approx. 20,000 times the strength of the Earth’s magnetic field), which allow recording a bit within a few nanoseconds (1 nanosecond = 0.000 000 001 second = 1000 picoseconds). One should emphasize that fast switching of strong magnetic fields is very difficult to achieve.
By harnessing the power of the much stronger internal forces of magnetic media, the members of an international research team have found a way to record information hundreds of times faster without the need for a magnetic field. Instead of the magnetic field, they used a heat pulse produced by a laser. Every nanomagnet in the material consists of billions of so-called spins, which act like magnets at the atomic scale and are strongly coupled by a so-called exchange interaction. This internal force aligns all the spins of a medium in one direction so the whole medium becomes “magnetic”.
COMPAMED.de; Source: Paul Scherrer Institute (PSI)