Nature: Hot magnets do it faster
An ultra-short pulse of one-twentieth of a millionth of a millionth of a second can switch a bit in a magnetic memory. That is a completely unexpected discovery, which former FOM researcher Dr. Alexey Kimel reported in an online article in Nature on 8 February 2012.
'Absolute nonsense,' says Kimel on the telephone from Grenoble where he is attending a congress today. His discovery – and the other recent work from researchers in the group of FOM workgroup leader Theo Rasing, professor of experimental solid state physics – is causing a considerable stir in the world of physics. 'Absolute nonsense, is what we thought when we discovered this. It is completely at odds with all our old ideas about magnetism.'
Changing pole
The atoms in the magnetic material are themselves all small mini-magnets, so-called spins. These can all point in the same direction with their North pole (then you have a normal magnet) or they can alternate in direction (then you have an anti-ferromagnet). An external force can change the direction of the poles. In computer hard disks that is achieved with another magnet and this is how we store information. At present that switch costs about one nanosecond, a thousandth millionth of a second.
Heat can do the same trick
Last year Kimel discovered something unexpected. With extremely short laser pulses (one-twentieth of a millionth of a millionth of a second) he could very briefly convert an anti-ferromagnet made of iron and gadolinium into a normal magnet. And that was worth an article in Nature. 'In that experiment we used a very small magnetic field and we were curious to know with just how little magnetic field that effect could still be achieved. To our great surprise the field was not needed at all; the heat of the laser pulse was enough. That was really interesting because heat has no direction, of course.'
The discovery could lead to much faster hard disks but as Kimel points out: ‘Real breakthroughs in science usually lead to applications that you could never dream of in advance.' And should this principle be applied on a large scale then it would need to be done with a different material. Gadolinium is a very scarce and expensive rare earth metal. 'We will now search for cheap, man-made materials that can be used instead.'
Kimel received an NWO Vidi grant and an ERC starting grant for this research. You can read more about this research on the website Science Now.