Manipulation of Gilbert damping in ultrathin half-metallic Co2FeAl1+x by composition-deficiency-compensation

Abstract

Gilbert damping is of crucial importance for spintronic devices due to its practical effect on the response time and energy consumption. Lower damping would enable more energy-efficient excitations and, thus, less current is needed. The Gilbert damping constant of the Co2FeAl film, a half-metal material important for spintronics with its 100% spin polarization at the Fermi level, has shown an abnormal increase at the thin film limit due to the inter-diffusion of Al atoms. Here, we report that the Gilbert damping of ultra-thin Co2FeAl1+x films of nanometer thicknesses can be effectively tuned by delicately controlling the stoichiometric ratio during the growth. Gilbert damping has been found to be the lowest of 0.065 in Co2FeAl1+0.1, which is deduced by ∼50% compared to that in Co2FeAl. We have further found that the damping constant of the ultra-thin Co2FeAl1+0.1 film is restored to the value of 0.062 of the nominal stoichiometric Co2FeAl by compensating the Al composition deficiency, as supported by 10.37% of composition change from scanning transmission electron microscopy with energy-dispersive-spectroscopy. This work offers a unique path to manipulate the Gilbert damping constant in ultra-thin Co2FeAl films by Al concentration control.