Abstract-Unifying ultrafast demagnetization and intrinsic Gilbert damping in Co/Ni bilayers with electronic relaxation near the Fermi surface

Wei Zhang, Wei He, Xiang-Qun Zhang, Zhao-Hua Cheng, Jiao Teng, and Manfred Fähnle

https://journals.aps.org/prb/accepted/c2075Y25Ia810e5b542200726ae86a14d2dd92127

The ability to controllably manipulate the laser-induced ultrafast magnetic dynamics is a prerequisite for future high speed spintronic devices. The optimization of devices requires the controllability of the ultrafast demagnetization time, \begin{figure}[htbp] } \label{fig1} \end{figure} , and intrinsic Gilbert damping, \begin{figure}[htbp] } \label{fig2} \end{figure} . In previous attempts to establish the relationship between \tauM and \alphaintr , the rare-earth doping of a permalloy film with two different demagnetization mechanism is not a suitable candidate. Here, we choose Co/Ni bilayers to investigate the relations between \begin{figure}[htbp] } \label{fig3} \end{figure} and \begin{figure}[htbp] } \label{fig4} \end{figure} by means of time-resolved magneto-optical Kerr effect (TRMOKE) via adjusting the thickness of the Ni layers, and obtain an approximately proportional relation between these two parameters. The remarkable agreement between TRMOKE experiment and the prediction of breathing Fermi-surface model confirms that a large Elliott-Yafet spin-mixing parameter b2 is relevant to the strong spin-orbital coupling at the Co/Ni interface. More importantly, a proportional relation between \tauM and \alpha \mbox{intr} in such metallic films or heterostructures with electronic relaxation near Fermi surface suggests the local spin-flip scattering domains the mechanism of ultrafast demagnetization, otherwise the spin-current mechanism domains. It is an effective method to distinguish the dominant contributions to ultrafast magnetic quenching in metallic heterostructures by investigating both the ultrafast demagnetization time and Gilbert damping simultaneously. Our work can open a novel avenue to manipulate the magnitude and efficiency of Terahertz emission in metallic heterostructures such as the perpendicular magnetic anisotropic Ta/Pt/Co/Ni/Pt/Ta multilayers, and then it has an immediate implication of the design of high frequency spintronic devices.https://journals.aps.org/prb/accepted/c2075Y25Ia810e5b542200726ae86a14d2dd92127