Modern hard drives in data centers store huge amounts of information thanks to tiny magnetic regions whose orientation sets the recorded data. Scientists are looking for ways to do this faster, and one promising approach involves ultrashort laser pulses capable of changing a material's magnetic order in tiny fractions of a second.
A team from the Joint Research Center 1242 at the University of Duisburg-Essen, together with colleagues from Helmholtz-Zentrum Berlin, studied how the thickness of an iron film affects so-called ultrafast demagnetization. In this process, a laser pulse causes the material to partially lose magnetic order over a very short time.
It turned out that the effect is stronger the thinner the iron layer. At a thickness of just 2 nanometers (two millionths of a millimeter), demagnetization was about 75% stronger than in a 16-nanometer layer, although the laser intensity remained the same. The results were published in the journal Advanced Science.
The reason lies in electron spins - the intrinsic magnetic moments of electrons, whose collective orientation provides iron's magnetism. "In particularly thin iron layers, a large proportion of these spins are at the interfaces of the material. There they have fewer neighboring spins with which they can interact magnetically," explains Dr. Andrea Eschenlohr from the physics faculty. "Simply put, the spins have less to hold on to. That is why it is easier for a laser pulse to disrupt their magnetic order."
Scientists had previously suspected that the thickness of the iron layer could affect demagnetization. What was unexpected was the size of the effect and the fact that it is linked specifically to the material's magnetic properties, rather than to differences in light absorption or atomic lattice vibrations.
In the long term, the discovery could help create magnetic storage media in which information is written by ultrashort laser pulses. However, several challenges must be solved before the technology can be deployed. For example, suitable laser sources will need to be integrated into electronic devices, and it will be necessary to precisely target very small areas to achieve high storage density.