Thomas Gigl

Positron spectroscopy of point defects in the skyrmion-lattice compound MnSi

Outstanding crystalline perfection is a key requirement for the formation of new forms of electronic order in a vast number of widely different materials. Whereas excellent sample quality represents a standard claim in the literature, there are, quite generally, no reliable microscopic probes to establish the nature and concentration of lattice defects such as voids, dislocations and different species of point defects on the level relevant to the length and energy scales inherent to these new forms of order. Here we report an experimental study of the archetypical skyrmion-lattice compound MnSi, where we relate the characteristic types of point defects and their concentration to the magnetic properties by combining different types of positron spectroscopy with ab-initio calculations and bulk measurements. We find that Mn antisite disorder broadens the magnetic phase transitions and lowers their critical temperatures, whereas the skyrmion lattice phase forms for all samples studied underlining the robustness of this topologically non-trivial state. Taken together, this demonstrates the unprecedented sensitivity of positron spectroscopy in studies of new forms of electronic order.

Detection and imaging of the oxygen deficiency in single crystalline YBa2Cu3O7−δ thin films using a scanning positron beam

Single crystalline YBa2Cu3O7−δ (YBCO) thin films were grown by pulsed laser deposition in order to probe the oxygen deficiency δ using a mono-energetic positron beam. The sample set covered a large range of δ (0.191 < δ < 0.791) yielding a variation of the critical temperature Tc between 25 and 90 K. We found a linear correlation between the Doppler broadening of the positron electron annihilation line and δ determined by X-ray diffraction. Ab-initio calculations have been performed in order to exclude the presence of Y vacancies and to ensure the negligible influence of potentially present Ba or Cu vacancies to the found correlation. Moreover, scanning with the positron beam allowed us to analyze the spatial variation of δ, which was found to fluctuate with a standard deviation of up to 0.079(5) within a single YBCO film.

Defect imaging and detection of precipitates using a new scanning positron microbeam

We report on a newly developed scanning positron microbeam based on threefold moderation of positrons provided by the high intensity positron source NEPOMUC. For brightness enhancement a remoderation unit with a

Ab-initio calculation of CDB spectra - a case study on transition metals

100\,

Positronbeam for μm Resolved Coincident Doppler Broadening Spectroscopy at NEPOMUC

nm thin Ni(100) foil and 9.6% efficiency is applied to reduce the area of the beam spot by a factor of 60. In this way, defect spectroscopy is enabled with a lateral resolution of

Ionic Liquid Loaded Silica Gel Particles Studied by Spatially Resolved DBS Using a Scanning Positron Beam

33\,\mu

Defects and Charging Processes in Li-Ion Battery Cathodes Studied by Operando Magnetometry and Positron Annihilation

m over a large scanning range of

Detection and imaging of the oxygen deficiency in single crystalline YBa

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