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

Abstract

The current density required for current induced magnetization switching in magnetic devices such as Magnetoresistive Random Access Memory (MRAM) is proportional to Gilbert damping constant. The lower damping would enable more energy-efficient excitations and thus less current needed. The Gilbert damping constant of the Co2FeAl film, a half-metal material important for spintronics with its 100% spin polarization at Fermi level, has shown the lowest Gilbert damping constant among the Heusler alloys. However, the increased Gilbert damping constant in ultra-thin Co2FeAl films is undesirable for low power consumption applications such as STT-MRAM. Being able to manipulate the Gilbert damping on demand is crucial for spintronic device engineering and optimization. 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. The 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 the 10.37% of composition change from the scanning transmission electron microscope energy-dispersive-spectroscopy. This work offers a unique path to manipulate the Gilbert damping constant in ultra-thin Co2FeAl films by Al concentration control.