Modulation of magnetic damping in antiferromagnet/CoFeB heterostructures

The modulation of antiferromagnetic (AFM) material and thermal annealing treatment on the magnetic damping of various AFM/CoFeB (CFB) samples have been systematically studied with the time-resolved magneto-optical Kerr effect. It is found the saturated magnetic damping factor αs increases considerably after introducing a thin MnIr or MnPt AFM layer. As a thin Al spacer of tAl = 0-2 nm is inserted, αs is found to decrease rapidly, reaching nearly the same value as that of the single CFB film at tAl = 2 nm. The result suggests that the AFM layer is not a good spin sink material and the surprisingly strong decrease in the damping factor is mainly attributed to the reduced direct exchange coupling between CoFe and Mn spins at the AFM/FM interface. Moreover, in spite of the exchange bias effect occurring or not, a similar monotonic increasing trend of αs with the increasing AFM layer thickness is observed for the as-deposited and annealed AFM/CFB samples, indicating that the enhanced magnetic damping at an elevated annealing temperature is mainly related to the increased interface roughness and atomic diffusion. These findings provide deeper insights into the role of the AFM/FM interface in magnetization dynamics, which will be helpful for future spintronic applications.