Scaling of All-Optical Switching to Nanometer Dimensions.

Here, we first demonstrate helicity-independent all-optical switching in GdCo, a material chosen for stronger perpendicular magnetic anisotropy (PMA) than GdFeCo but with similar ferrimagnetic properties; furthermore, we achieve reliable AOS down to 200 nm diameters. The greater challenge to scaling was maintaining the perpendicular magnetic anisotropy for smaller dot dimensions, as was found to be a challenge in. While ion milling is a common method for patterning MTJ pillars for MRAM, it was found to destroy the integrity of the PMA. Instead, a lift-off process with electron -beam lithography was used to pattern the nanodots, ranging in size from 15 pm down to 50 nm, into arrays. Each dot size of diameter d was arrayed with a pitch of 3d in a25 pm x 25 pm square region. The pitch was chosen to be large enough to prevent magnetistatic coupling between the dots, while simultaneously allowing a high areal density of the dots for maximum magnetic signal during subsequent optical measurements.