Tuning interfacial spin pump in Ta/CoFeB/MgO films by ultrafast laser pulse

Abstract

The operation speed and the energy-efficiency of magnetic random access memory (MRAM) is largely controlled by Gilbert damping of magnetic layers. The ultrafast laser pulse may offer an opportunity to tune the interfacial spin pumping, which can then control the Gilbert damping. Here, we have investigated the ultrafast laser induced magnetization precession, especially the magnetic damping, of a series of Ta/CoFeB/MgO thin films using the pump–probe time-resolved magneto-optical Kerr effect (TR-MOKE) measurements. The pump fluence dependence of the magnetic damping has been found to vary with the thickness tCoFeB of the nanoscale CoFeB layer. Remarkably, the intrinsic damping constant α0 has been found to decrease with the increase in the pump fluence when the thickness of the CoFeB layer is less than 1.2 nm. This fluence-dependent behavior of α0 is attributed to the fluence-dependent contribution of the Ta/CoFeB interface induced spin pumping effect. The ultrafast laser pulses effectively enhance the interfacial spin pumping effect via tuning the spin diffusion length of the adjacent Ta layer, from 2.4 to 7.1 nm. Our findings provide insights into the ultrafast laser pulse driven magnetic dynamics and interfacial spin manipulation in Ta/CoFeB/MgO structures.