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Spin angular momentum transfer in magnetic bilayers offers the possibility of ultrafast and low-loss operation for next-generation spintronic devices. We report the field- and temperature- dependent measurements on the magnetization precessions in Co2FeAl/(Ga,Mn)As by time-resolved magneto-optical Kerr effect. Analysis of the effective Gilbert damping and phase shift indicates a clear signature of an enhanced dynamic exchange coupling between the two ferromagnetic (FM) layers due to the reinforced spin pumping at resonance. The temperature dependence of the dynamic exchange-coupling reveals a primary contribution from the ferromagnetism in (Ga,Mn)As.

Optical control of magnetic anisotropy in ferromagnetic (FM) metals via non-thermal effects offers an intriguing route for the ultrafast magnetization control. Here, we report on strong modification of exchange-coupling induced uniaxial magnetic anisotropy (UMA) in Fe/CoO below the Néel temperature of CoO owing to the charge transfer excited by ultrafast laser pulses. This UMA modification by nonthermal effects is manifested as much smaller frequencies of the Fe spin precession in the initial 100-ps time range under the 400-nm pump with charge transfer excitation, compared to the 800-nm pump with pure thermal effects. From the time-dependent frequency shift under a moderate pump fluence of 0.5 mJ/cm2, we determined the magnitude of the UMA attenuation with a highest value of more than 1000 Oe in a duration of 100 ps. The strong UMA attenuation is attributed to the large suppression of the interface exchange coupling as a result of the diminishment of antiferromagnetic (AFM) spin order in CoO. Our results give insights into the ultrafast spin modulation in AFM CoO dominated by the electronic process, which can be utilized for efficient driving of the coherent spin motion in the proximate FM metal exchange coupled to CoO.

Using an ultrafast laser pulse as a substitution of continuous-wave laser to excite a magnetic film leads to high spin temperature and fast demagnetization, beneficial to the rapid and efficient photo-assisted magnetization (M) reversal. Here, ultrafast laser induced M reversal in perpendicular magnetic anisotropy L10 FePt films with different chemical ordering parameter (from S<0.6 to S>0.9) was investigated using magneto-optical Kerr effect (MOKE). It was found that the coercive field (Hc) without laser excitation increases from ∼0.8 to ∼4 kOe with increasing S, but Hc becomes smaller for enhanced laser fluence (F) and reaches an analogous small value of ∼0.2 kOe for F>12 mJ cm-2. Despite such a significant softening in films with high S, the laser induced M reversal rate is slightly less than 1 even for the applied field (H) much larger than 0.2 kOe. This reveals a small portion of spins are photo inactively pinned, as confirmed by magnetic force microscopy measurements. Such pinning sites may be reduced with improved chemical order and morphology. We also found an approximately inverse linear relation between the H and the corresponding threshold F to induce the M reversal in the film of high S, which can be described by an ultrafast thermal activated spin flip model.