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Antiferromagnetic CuMnAs thin films have attracted attention since the discovery of the manipulation of their magnetic structure via electrical, optical, and terahertz pulses of electric fields, enabling convenient approaches to the switching between magnetoresistive states of the film for the information storage. However, the magnetic structure and, thus, the efficiency of the manipulation can be affected by the film morphology and growth defects. In this study, we investigate the properties of CuMnAs thin films by probing the defect-related uniaxial anisotropy of electric conductivity by contact-free terahertz transmission spectroscopy. We show that the terahertz measurements conveniently detect the conductivity anisotropy, that are consistent with conventional DC Hall-bar measurements. Moreover, the terahertz technique allows for considerably finer determination of anisotropy axes and it is less sensitive to the local film degradation. Thanks to the averaging over a large detection area, the THz probing also allows for an analysis of strongly non-uniform thin films. Using scanning near-field terahertz and electron microscopies, we relate the observed anisotropic conductivity of CuMnAs to the elongation and orientation of growth defects, which influence the local microscopic conductivity. We also demonstrate control over the morphology of defects by using vicinal substrates., 33 pages, 16 figures

This thesis is focused on a detailed investigation of the optically induced quench switching effect in different films of antiferromagnetic CuMnAs. The quench switching effect was recently discovered to be highly reproducible resistance switch- ing, which can be excited by electrical and optical laser pulses. This thesis com- pares the amplitude response to laser-induced quench switching for samples on the different substrate material, samples with different stoichiometries, and sam- ples with different thicknesses of CuMnAs film. The effects of different ratios between the laser spot and the size of the measured device are investigated, and position-dependent measurements are also presented. It is shown that resistivity change with optical excitation using a single 120 femtosecond laser pulse can, in ideal conditions, reach up to 15% at room temperature, which is comparable with the maximum signal obtained with electrical pulses. All of the measure- ments combined with current knowledge of quench switching illustrate the robust behavior of this mechanism across a wide range of conditions. 1

This thesis contains detailed study of a newly discovered effect of quench switch- ing in thin films of antiferromagnetic CuMnAs. This effect can be used to induce highly reproducible resistance switching behaviour in response to electrical or optical laser pulsing. The resistance changes reach up to GMR-like values of 20 % at room temperature and 100 % at low temperatures. We attribute these changes to the nano-fragmentation of magnetic domain structure. After CuMnAs is pulsed into a high resistance state, a characteristic period of time follows, during which the resistance relaxes back to the original value. This relaxation can be described by Kohlrausch stretched exponential function. This type of relaxation is characteristic for behaviour of correlated complex systems, which goes well with the idea of highly fragmented and correlated magnetic states of quenched CuMnAs. The quench switching effect is studied in detail on devices with different geometries, for various parameters of the writing pulse, as well as growth pa- rameters of the CuMnAs films. The switching is demonstrated in CuMnAs films prepared on GaP, GaAs and Si substrates, where the quality of the film differs. This illustrates robustness and application potential of the effect. 1

In this thesis we studied precession mechanism in ferromagnetic thin film half-metal NiMnSb. We measured magnetization oscillations using optical pump and probe experiment at temperatures between 15 and 200 K and we evaluated the magnetic anisotropy fields, spin stiffness and Gilbert damping. New setup for ferromagnetic resonance measurement was built utilizing vector network analyser. With this setup we measured FMR at temperatures between 300 and 75 K. We evaluated the same parameters from FMR experiments as from the optical one. We found very good agreement in results obtained by the two methods. Powered by TCPDF (www.tcpdf.org)