  The impact of the local chemical environment on the Gilbert damping in the
binary alloy Fe$_{100-x}$Co$_{x}$ is investigated, using computations based on
density functional theory. By varying the alloy composition x as well as Fe/Co
atom positions we reveal that the effective damping of the alloy is highly
sensitive to the nearest neighbor environment, especially to the amount of Co
and the average distance between Co-Co atoms at nearest neighbor sites. Both
lead to a significant local increase (up to an order of magnitude) of the
effective Gilbert damping, originating mainly from variations of the density of
states at the Fermi energy. In a global perspective (i.e., making a
configuration average for a real material), those differences in damping are
masked by statistical averages. When low-temperature explicit atomistic
dynamics simulations are performed, the impact of short-range disorder on local
dynamics is observed to also alter the overall relaxation rate. Our results
illustrate the possibility of local chemical engineering of the Gilbert
damping, which may stimulate the study of new ways to tune and control
materials aiming for spintronics applications.
