Light is the most energy-efficient way for transmitting information. However, it is not easy to store light. That is why data centres are still using magnetic hard disks, but with this the information transfer requires much more energy. Researchers from the Institute of Photonic Integration at the TU Eindhoven have, however, presented a ‘hybrid technique’ in the journal Nature Communications, that combines the advantages of light and magnetic storage. Ultra-short light pulses enable information to be written directly to a magnetic memory in a fast and energy-efficient manner.

Magnetic domains

Data 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 ferrimagnets

Conventionally, 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.
 
The 'on-the-fly' writing of data in a racetrack memory. The magnetic bits (ones and zeros) are written with laser pulses (red pulse, left side). These subsequently move along the racetrack (black arrows). In the future, the data may also be read optically (red pulse, right side). Illustration: TU Eindhoven.

Nano scale

The 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