Interlayer modulation on the dynamic magnetic properties of L 1₀-FePt/NM/[CoNi]₅ composite film structures

The magnetization precession dynamics is systematically studied in L1₀-FePt/NM/[CoNi]₅ exchange-coupled films using the time-resolved magneto-optical Kerr effect technique, where the nonmagnetic interlayer is Ta or Pt. It is demonstrated that the precession frequency f decreases dramatically with the increasing interlayer thickness of Ta (t_Ta) or Pt (t_Pt). By fitting the f ∼H curves of different t_Ta with the coherent precession model including the interfacial coupling interaction, the exchange coupling strength as well as the magnetization orientations of FePt and [CoNi]₅ are determined. Meanwhile, it is found the magnetic damping constant α can be modulated considerably as well by adjusting the interlayer thickness. For the Ta interlayer, the α value decreases gradually with the increase in t_Ta as the result of decreased coupling strength, while it shows a monotonic increasing behavior for the Pt layer. The increased α with t_Pt can be attributed to the enhanced spin pumping contribution from Pt, which greatly exceeds the decreasing tendency caused by the reduced interfacial coupling. This study provides deep insights into the dynamic behaviors of the exchange-coupled magnetic system, which are valuable to achieve effective control of the ultrafast magnetization dynamics for spintronic applications.