Optical Switching with Spintronics

All-optical switching. Data is stored in the form of bits. Data writing is achieved by switching the direction of the poles via the application of short laser pulses. (Source: TU Eindhoven)

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. Researchers of the Institute of Photonic Inte­gration of the Eindhoven Univer­sity of Tech­nology have developed a “hybrid tech­nology” which shows the advantages of both light and magnetic hard drives. Femto­second light pulses allows 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. This research promises to revolu­tionize the process of data storage in future photonic inte­grated circuits.

Data are stored in hard drives in the form of ‘bits’, tiny magnetic domains with a North and a South pole. Conven­tionally, the switching occurs when an external magnetic field is applied, which would force the direction of the poles either up or down. Alter­natively, switching can be achieved via the application of a short femto­second laser pulse in an all-optical switching, and results in a more effi­cient and much faster storage of data. Mark Lalieu, PhD candidate at the Applied Physics Depart­ment, says: “All-optical switching for data storage has been known for about a decade. 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, under the guidance of Reinoud Lavrijsen and Bert Koopmans, was able to achieve all-optical switching 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. He says: “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 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. Koopmans says: “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. From a ‘photonic Thalys’ to a ‘magnetic ICE’, without any inter­mediate stops. You will under­stand the enormous increase in speed and reduction in energy consump­tion that can be achieved in this way”.

This 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 busy with the inves­tigation on the read-out of the magnetic data, which can be done all-opti­cally as well. (Source: TU Eindhoven)

Reference: M. L. M. Lalieu et al.: Integrating all-optical switching with spintronics, Nat. Commun. 10, 110 (2019); DOI: 10.1038/s41467-018-08062-4

Link: Institute for Photonic Integration, Eindhoven University of Technology, Eindhoven, The Netherlands

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