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Eindhoven team develops hybrid data storage with optical and magnetic drives

17 Jan 2019

Next-generation photonic memory devices are ‘light-written’, ultrafast and energy efficient,

Researchers at the Institute of Photonic Integration of the Eindhoven University of Technology (TU/e) have developed a hybrid technology featuring the advantages of both optical and magnetic hard drives. Ultra-short (femtosecond) light pulses allows data to be directly written in a magnetic memory in a fast and highly energy-efficient way, say the developers.

TU/e comments, “Light is the most energy-efficient way of moving information. Yet, light shows one big limitation: it is difficult to store. As a matter of fact, data centers rely primarily on magnetic hard drives. However, in these hard drives, information is transferred at an energy cost that is nowadays exploding.”

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. The research, which has just been published in Nature Communications, promises to revolutionize the process of data storage in future photonic integrated circuits.

Synthetic ferrimagnets

Conventionally, the switching required for storage occurs when an external magnetic field is applied, which would forces the polarity of the storage “bits” either up (1) or down (0). Alternatively, switching can be achieved via the application of a short (femtosecond) laser pulse – “all-optical switching” – and results in a more efficient and more rapid storage of data.

Mark Lalieu, PhD candidate at the Applied Physics Department of TU/e commented, “When all-optical switching was first observed in ferromagnetic materials, amongst the most promising materials for magnetic memory devices, this research field gained a great boost. However, the switching of the magnetization in these materials requires multiple laser pulses and, thus, long data writing times.”

Lalieu, guided by Reinoud Lavrijsen and Bert Koopmans, achieved all-optical switching in synthetic ferrimagnets using single femtosecond laser pulses, thus exploiting the high velocity of data-writing and reduced energy consumption.

So how does all-optical switching compare to modern magnetic storage technologies? Lalieu explained, “The switching of the magnetization direction using the single-pulse all-optical switching is in the order of picoseconds, which is about a 100 to 1000 times faster than what is possible with today’s technology. Moreover, as the optical information is stored in magnetic bits without the need of energy-costly electronics, it holds enormous potential for future use in photonic integrated circuits.”

In addition, Lalieu integrated all-optical switching with the 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, thus, new data to be stored.

‘On the fly copying’

Koopmans commented, “This ‘on the fly’ copying of information between light and magnetic racetracks, without any intermediate electronic steps, is like jumping out of a moving high-speed train to another one. You will understand the enormous increase in speed and reduction in energy consumption that can be achieved in this way.”

The research was performed on micrometric wires. In the future, smaller devices in the nanometer scale should be designed for better integration on chips. In addition, working towards the final integration of the photonic memory device, the Physics of Nanostructure group is currently also investigating the read-out of the magnetic data, which can be done all-optically as well.

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