Giant spin Hall effect and spin-orbit torques from 5d transition metal - aluminum alloys for energy efficient synthetic antiferromagnetic racetrack memories

Synthetic antiferromagnetic thin film stacks are an essential component for racetrack memory and magnetic tunnel junction devices. The magnetic layers in these devices must display perpendicular magnetic anisotropy (PMA) that is typically derived from interfaces between [111] crystallographically textured layers of Co and Ni. Here, we show that 5d transition metal-Al alloy sputtered thin films that display an L1₀ structure even for room temperature deposition both show large PMA as well as giant spin Hall effects that give rise to giant spin orbit torques. Using the L1₀ compound RuAl as a AF spacer layer we demonstrate novel synthetic antiferromagnets with an entire L1₀ structure that are, moreover, crystallographically ordered along the [001] orientation and yet demonstrate high PMA. We demonstrate state-of-the-art racetrack memory devices that exhibit a several-fold increased efficiency for current induced domain wall motion as compared to prior-art materials. These structures are formed on thin Ir_xAl_100-x underlayers with an L1₀ structure and are composed of ultra-thin layers of cubic Co and Ni with the L1₀ RuAl as the antiferromagnetic coupling spacer layer. These structures exhibit chiral Néel -type domain walls so that all the domain walls move synchronously along the racetracks at very high speeds under the influence of nano-second long current pulses. Moreover, the domain walls show very high thermal stability after repeated motion backwards and forwards along the racetracks. These novel materials based on L1₀ compounds provide a new route for the multifunctional use of racetrack memories that are compatible with complementary metal-oxide semiconductor technologies.