Light is the most energy-efficient way to move information; however, light shows one big limitation: it is difficult to store. Data centers, for example, rely primarily on magnetic hard drives in which information is transferred at an energy cost that is increasing. A hybrid technology was developed that shows advantages of both light and magnetic hard drives.
Ultra-short (femtosecond) light pulses allow data to be directly written in a magnetic memory in a fast and highly energy-efficient way. Moreover, as soon as the information is written (and stored), it moves forward, leaving space to empty memory domains to be filled in with new data.
Data are stored in hard drives in the form of bits — tiny magnetic domains with a North and a South pole. The direction of these poles (magnetization) determines whether the bits contain a digital 0 or a 1. Writing the data is achieved by switching the direction of the magnetization of the associated bits. Conventionally, the switching occurs when an external magnetic field is applied, which would force the direction of the poles either up (1) or down (0). Alternatively, switching can be achieved via the application of a short (femtosecond) laser pulse, called all-optical switching, and results in more efficient and much faster storage of data.
All-optical switching was achieved in synthetic ferrimagnets — a material system highly suitable for spintronic data applications — using single femtosecond laser pulses, thus exploiting the high velocity of data writing and reduced energy consumption.
The switching of the magnetization direction using single-pulse, all-optical switching is in the order of picoseconds — about 100 to 1,000 times faster than what is possible with today's technology. Moreover, as the optical information is stored in magnetic bits without the need of costly energy electronics, it holds potential for future use in photonic integrated circuits.
All-optical switching was integrated with so-called racetrack memory — a magnetic wire through which the data, in the form of magnetic bits, is efficiently transported using an electrical current. In this system, magnetic bits are continuously written using light and immediately transported along the wire by the electrical current, leaving space to empty magnetic bits and store new data. This on-the-fly copying of information between light and magnetic racetracks, without any intermediate electronic steps, is like jumping from one moving high-speed train to another.
The research was performed on micrometric wires; smaller devices on the nanometer scale should be designed for better integration on chips.