Magnetic domainsData is stored on a hard disk in the form of ‘bits’, minuscule magnetic domains with a North and a South pole. The direction of these poles (‘magnetisation’) determines whether the bits contain a digital 0 or a 1. Writing of the data is achieved by switching the magnetisation of the relevant bits.
Synthetic ferrimagnetsConventionally, this switching takes place by applying an external magnetic field that forces the direction of the poles either up (1) or down (0). An alternative is to achieve this switching optically, by using a very short (femtosecond) laser pulse. With this, data storage can potentially be much faster and more efficient. The researchers succeeded in realising this optical switching using so-called synthetic ferrimagnets – materials that are eminently suitable for spintronics applications. This was achieved with a single femtosecond laser pulse, which means the writing of the information is energy-efficient and fast.
Writing data ‘on-the-fly’Furthermore, the researchers combined this optical switching with a so-called racetrack memory, a magnetic wire in which the data, in the form of magnetic bits, is transported efficiently with the aid of an electric current. In this system, the data is stored continuously in the magnetic bits using light and these bits are then immediately transported along the wire because of an electric current, which then frees up space for empty magnetic bits and therefore new information can be stored. This ‘on-the-fly’ copying of information between light and magnetic racetracks, without intermediate electronic steps, is just like jumping back and forth between two moving, high-speed trains, instead of changing to another train at a station. This is obviously much faster and energy-efficient.
Nano scaleThe research was carried out with micro wires. In the future these need to be reduced to nano scale to enable integration with computer chips. The research group Physics of Nanostructures is also working on the optical reading of the (magnetic) data.
Source: TU Eindhoven