Gilbert Damping in Single-Crystalline Ni/MgO(001)*

The dynamical properties of Nickel and Nickel alloys are of great interest in spintronic applications, as these materials exhibit low coercivity and significant magnetoresistance, however, the interplay of the various damping mechanisms, such as two magnon scattering and local resonance, is not well understood. The frequency, $\omega$, and Gilbert damping, $\alpha$, behavior of uniform spin precession on Ni/MgO(001) are studied over a wide range of external field angles and magnitudes using the Time-Resolved Magneto-Optical Kerr effect (TR-MOKE). The damping parameter shows a strong dependence on the magnetocrystalline anisotropy, suggesting a tuneability of $\alpha$ over the range of 0.09 to 0.5. Two separate trends in $\alpha$ vs. $\omega$ are observed depending on the magnitude and direction of the applied field when applied in-plane, indicating the presence of competing damping mechanisms. We further investigate these properties in measurements in which the external field is applied normal to the sample plane, thereby minimizing the role of two magnon scattering.