Spintronic ferromagnetic/non-magnetic heterostructures are novel sources for the generation of THz radiation based on spin-to-charge conversion in the layers. The key technological and scientific challenge of THz spintronic emitters is to increase their intensity and frequency bandwidth. Our work reveals the factors to engineer spintronic Terahertz generation by introducing the scattering lifetime and the interface transmission for spin polarized, non-equilibrium electrons. We clarify the influence of the electron-defect scattering lifetime on the spectral shape and the interface transmission on the THz amplitude, and how this is linked to structural defects of bilayer emitters. The results of our study define a roadmap of the properties of emitted as well as detected THz-pulse shapes and spectra that is essential for future applications of metallic spintronic THz emitters.

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We present a study of the influence of the annealing temperature Ta on the magnetic properties of Co40Fe40B20 thin films. Using a vector network analyzer ferromagnetic resonance (VNA-FMR) setup and the magneto-optical Kerr effect, the dependence of the Gilbert damping parameter α, the exchange constant A, the saturation magnetization as well as the coercive field and the Kerr signal on Ta is reported. Additionally, the correlation with the crystalline properties of the films studied by X-ray diffractometry is discussed. We found that while the damping parameter α and the coercive field show sharp changes starting at a certain Ta value, the exchange constant A and the Kerr signal show a steady evolution. A differential modification of the film surface compared to the bulk is discussed as a possible reason. In any case, we found that the low damping values are preserved at the first onset of crystallization.

We examine the influence of crystal growth on the spin-pumping induced inverse spin Hall effect in Fe/Pt bilayers. The morphology of the Fe/Pt interface influences the effective spin mixing conductance. The increase of growth temperature leads to smoother and larger grains at the interface that enhance the effective spin mixing conductance. The spin current injection efficiency into Pt, measured by the inverse spin Hall effect, is maximized by optimizing the epitaxy of Pt on Fe. In magnetic field dependent measurements, the presence of a strong magnetic anisotropy gives rise to two distinct inverse spin Hall effect voltage peaks.Magnon spintronics -an emerging sub-field of spintronics in which magnons, the quasi-particles of the magnetization dynamics, are used as information carriershas attracted considerable attention in the last years. 1,2 A powerful method to detect magnons is the combination of spin pumping and the inverse spin Hall effect. The spin-pumping effect allows for the injection of a spin current from a ferromagnetic (FM) layer into an attached non-magnetic metal (NM) layer. 3 This spin current is subsequently transformed into a charge current by the inverse spin Hall effect (ISHE). 1,4 Many aspects of magnetization dynamics in FM/NM bilayers have been investigated by means of spin pumping and ISHE in various kinds of materials. 5 A prominent material combination is Ni 80 Fe 20 (Py) and Pt bilayers. 6,7 In these kind of metallic heterosystems, the dependencies of the spin-pumping induced ISHE voltage on the saturation magnetization and the damping constant, 8 on the geometry 6 and on the thicknesses of the individual layers 9 have been investigated. Recently, it has been shown that the spin-pumping mechanism is even applicable in insulating FM/NM bilayers like YIG/Pt (YIG:yttrium iron garnet). 2,10-18 Investigations on standing 18 as well as propagating 17 magnons in a wide range of wavelengths 15,16 by a combination of spin pumping and ISHE have been performed. Furthermore, the YIG and Pt thickness dependence on the ISHE-voltage from spin pumping 12-14 and nonlinear spin pumping 11 has been observed.Although spin pumping is an interfacial effect, the manner in which it, and therefore the ISHE signal strength, is affected by the structural parameters of the interface have so far not been investigated in detail. Recently, the role of the cleanliness of the YIG suface, 10 and the crystal perfection of YIG 19 in the YIG /Pt system proved the great importance of the interface properties. However in metallic systems the study of the influence of a) FIG. 1. (left) Schematic diagram of the sample structure with the corresponding thicknesses. Ferromagnetic resonance is excited by a microwave magnetic field induced by a Cu microstrip antenna and a tunable magnetic external field (Hext) while a silicon oxide plate isolates the Pt from the Cu antenna. (right) Scheme of the geometry used for FMR and ISHE measurements.the growth modes is limited. For example, it is not clear to what extend the polycrystalline n...

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