Time: Wednesday, October 24th, 17:50
Speaker: Jeffrey BOKOR, Berkeley
Single‐shot helicity independent all optical switching (AOS) of GdFeCo ferrimagnetic alloys has received considerable attention since it was first reported in 2011 [1] and has been understood as arising from an ultrafast thermal effect [2]. We have demonstrated that ultrafast heating of GdFeCo may be achieved by electrical charge current pulses from an electronic circuit [3]. We observe deterministic, repeatable, and reversible ultrafast switching of the magnetization of GdFeCo with a single sub‐10 picosecond electrical current pulse. The magnetization reverses in ~10 ps, which is more than one order of magnitude faster than any other electrically controlled magnetic switching, and demonstrates a fundamentally new switching mechanism without the need for spin polarized currents or spin transfer/orbit torques. The original observation of all‐optical switching was limited to GdFeCo [1, 2]. In 2014 it was discovered that all‐optical switching could be obtained in a range of ferromagnetic films [3]. However, it has now been understood that, in the ferromagnets that have been tested to date, all‐optical switching is a multi‐shot process [5]. This means that for full magnetization reversal to occur, multiple laser pulses are needed, which limits the operation speed. We have experimentally demonstrated a new family of ferromagnets grown on GdFeCo which present single‐shot all optical switching [6]. These coupled bilayer stacks may offer distinct advantages of ferromagnets over pure ferrimagnets for applications, including ultrafast electric current switching of ferromagnets, thereby enabling a high magnetoresistance electrical readout. We are also studying scaling of the required switching current with size of the magnetic element down to 50 nm dots and smaller. Results on switching of such nanoscale magnetic dots in GdFeCo as well as a number of new ferrimagnetic materials will be presented. Our long‐term goal is to realize fully integrated devices suitable for on‐chip magnetic memory (and perhaps even logic) that can be switched with current delivered by an on‐chip CMOS drive circuit (no laser involved!) with switching speed in the range of picoseconds, i.e. up to two orders of magnitude faster than present spin‐torque based spintronics.
[1] I. Radu, et al., Nature 472, 205 (2011).
[2] T. A. Ostler, et al., Nat Commun 3, 666 (2012).
[3] Y. Yang, et al., Science Advances 3, E1603117 (2017).
[4] C. H. Lambert, et al., Science 345, 1337 (2014).
[5] M. S. El Hadri, Phys. Rev. B 94, 064412 (2016).
[6] J. Gorchon, et al., Appl. Phys. Lett. 111 (2017).