Fig. 1
(a) Schematic of tr-MOKE experiment: A 1.55 eV pump pulse excites the sample, followed by probing at different photon energies-3.1 eV in the visible range and 67 eV and 72.5 eV in the extreme ultraviolet (EUV) range. The inset depicts the FeNi/FePt bilayer system with varying FeNi thicknesses. Blue arrows indicate the magnetization easy axis for FeNi and FePt. The red-shaded region highlights the pump-probe penetration depth, while the bold blue arrow represents the average magnetization canting detected by the probe pulse. (b) MFM phase maps: Magnetic force microscopy (MFM) images (2 \({\upmu }\)m \(\times\) 2 \({\upmu }\)m) display the FeNi/FePt system with FeNi thicknesses ranging from 30 nm to 6 nm. All maps use a consistent color contrast for direct comparison. Notably, FeNi(12)/FePt and FeNi(6)/FePt exhibit a higher density of bright regions due to enhanced out-of-plane magnetization. (c) Static longitudinal MOKE measurements: Magneto-optical Kerr effect (MOKE) data for FeNi and FeNi/FePt composites show variations in magnetization as a function of FeNi thickness. (d) Magnetization dynamics: Time-resolved magnetization measurements reveal ultrafast demagnetization followed by recovery. FeNi(30) and FeNi(30)/FePt exhibit slower recovery dynamics, while FeNi(6)/FePt and FeNi(12)/FePt show ultrafast demagnetization accompanied by a transient rotation of magnetization vector with an increase of its in-plane component on femtosecond timescales before recovery.
