The authors gratefully acknowledge ﬁnancial support via the German Academic Exchange Service, Spanish MINECO grant under research Project No. MAT2013-48054-C2-2-R, the German Priority Program SPP 1536 “SpinCAT” funded by the Deutsche Forschungsgemeinschaft (DFG), and the excellence clusters “The Hamburg Centre for Ultrafast Imaging” funded by the DFG and “Nanospintronics” funded by the State of Hamburg. Scientiﬁc support from the University of Oviedo SCTs is also acknowledged. Work carried out in Budapest was supported by the Hungarian Scientiﬁc Research Fund under Grant No. OTKA K 104696.