Magnetization precession and damping in Co ₂ FeSi Heusler alloy thin films

Magnetization dynamics of Co ₂ FeSi full Heusler alloy films have been investigated by time-resolved magneto-optical Kerr effect (TR-MOKE). For the samples grown at a substrate temperature (T _s ) lower than 350 °C, an obvious dual frequency phenomenon is found in the TR-MOKE signals due to the coexistence of a strong main precession mode and a weak additional mode. The amplitude of the additional high frequency mode decreases and becomes undetectable with increasing T _s . On the contrary, the magnetic damping parameter α ₀ measured at the highest external field of H = 15kOe is as low as 0.004 for low T _s samples, it rises abruptly at T _s > 350 °C and even reaches 0.023 at T _s = 480 °C in spite of the improved atomic ordering. We attribute the greatly increased magnetic damping to the enhanced two-magnon scattering occurred at grain-grain boundaries. This study provides a comprehensive insight into the spin precession and magnetic damping behaviors of Heusler alloy films, which will be helpful for developing high frequency spintronic devices.