Spintronics: Fast-switching magnetic tunnel junctions

In spin transport electronics, also known as spintronics, it is not the charge of the electron that acts as the carrier of information – it is the electron’s spin. As spins are ‘sensitive’ to the magnetic properties of a given material, the field of spintronics – which was born at the end of the eighties and has since evolved at a steady rate – holds much promise for the development of high-performance microelectronic systems. This is a short highlight on a paper where a spintronic device and optical control at short time scales play the leading roles.


To live up to its promise, it is crucial for spintronics technology to achieve control over magnetic behaviour without recurring to strong external magnetic fields. Spin-torque and electric-field-assisted switching of the magnetization suffer from operating speeds above tens of picoseconds. Optical manipulation enables magnetization reversal on shorter times scales, and for this reason all-optical switching (AOS) with femtosecond laser pulses has been recently investigated in a range of magnetic systems. Jun-Yang Chen and collaborators now report ultrafast AOS of a realistic spintronic device, namely a magnetic tunnel junction (MTJ), using subpicosecond laser pulses at telecom wavelengths. The considered MTJ, described as a pillar with a diameter of 12 μm, features ferrimagnetic Gd(Fe,Co) as the free layer and MgO for the tunneling barrier. All-optical switching of the device is achieved by illuminating the MTJ with a train of 0.4-ps-long pulses at a repetition rate of 0.5 Hz. Monitoring an averaged value of the tunneling magnetoresistance (TMR) over time shows that each laser pulse switches the MTJ between its low and high resistance states, corresponding to a variation in TMR by 0.6 ± 0.05 Ω. The team could also demonstrate AOS with 1-MHz repetition rate on a simpler Hall-effect Gd(Fe,Co) device, using trains of multiple pulses with a pulse-to-pulse spacing of 1μs. In the light of the obtained results, the authors expect further work on optically switchable MTJs to lead to the development of novel optospintronic systems.

Phys. Rev. Applied 7, 021001 (2017)


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