Gilbert Damping in Annealed Perpendicular Exchange Biased CoFeB/Pt/MnIr Multilayers

Exchange bias and intrinsic Gilbert damping α0 are two important parameters in magnetic multilayers. To explore the correlation between exchange coupling and damping, the samples Ta (2.6nm)/Pt (2.5nm)/Co62Fe25B13 (0.63nm)/Pt (0.5nm)/Mn78Ir22 (t)/Ta (4nm) are deposited by using pulsed-DC magnetron sputtering. The static and dynamic magnetic responses with different thickness of antiferromagnetic MnIr are investigated using vibrating sample magnetometer (VSM) and the pump-probe time-resolved magneto-optical Kerr effect (TR-MOKE). The exchange bias initially increases and then decreases with increasing thickness of MnIr layer, which is associated with the interfacial exchange coupling. The dynamic results demonstrate that the Gilbert damping of CoFeB/Pt/MnIr can increase by up to 40% compared with CoFeB/Pt. Based on the fact that the spin pumping has been excluded because of the Pt interlayer, we attribute the enhancement in Gilbert damping to the exchange coupling between AFM and FM.