This thesis investigates the ultrafast loss and recovery of ferromagnetic (FM) and antiferromagnetic (AFM) order in exchange-coupled metallic FM/AFM and FM/AFM/FM heterostructures using time-resolved resonant x-ray magnetic circular (R-XMCD) and linear dichroism (R-XMLD) measurements in reflectivity geometry. The work examines how an AFM layer and its spin structure influence the ultrafast dynamics of adjacent FM layers, as well as the intrinsic dynamics of the AFM itself following ultrashort optical excitation. Tailored Co/Mn/Co trilayers and Mn2Au/Fe bilayers exhibiting specific magnetic couplings were grown using molecular beam epitaxy (MBE) and characterized structurally and magnetically using Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and magneto-optical Kerr effect (MOKE) measurements. The experimental findings of this thesis are organized in three main studies. The first investigates the ultrafast magnetization dynamics of two FM Co layers interlayer-exchange-coupled through an AFM Mn spacer layer. An accelerated demagnetization is observed in case of a collinear Mn spin structure, attributed to an enhanced optically induced intersite spin transfer (OISTR) between Co and Mn, with results qualitatively reproduced by ab initio time-dependent density-functional theory (TD-DFT) calculations. The second study focuses on the epitaxial growth of AFM Mn2Au on gold-capped Nb(001) and Ta(001) substrates. Layer-by-layer growth on the gold-capped Nb(001) substrate is observed. Magnetic coupling to an adjacent FM Fe layer reveals distinct coupling and non-coupling areas on the sample, resulting in a partial exchange-bias (EB) shift after field cooling. These regions are locally identified and quantitatively analyzed via Kerr microscopy, revealing dimensions of tens of µm. The final study examines the ultrafast loss and recovery of AFM and FM order in a strongly magnetically coupled Mn2Au/permalloy (Py) bilayer following ultrashort laser excitation. A remarkably fast recovery of AFM order, within 2-3 ps, is observed in the Mn2Au layer, occurring 1-2 orders of magnitude faster than the FM order recovery in the adjacent Py layer. So far, the observed AFM dynamics could not be fully reproduced by an atomistic spin model coupled to a two-temperature model for a simple Mn2Au layer. Absorption calculations for both pump and probe pulses reveal that only surface-near Mn2Au layers are probed, where the excitation is 2-3 times more intense than in bulk layers. These findings demonstrate that AFMs enable ultrafast spin dynamics, highlighting their potential in future THz spintronic devices.
