Browsing by Author "Clauß, Conrad"

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    On-chip broadband magnetic resonance spectroscopy down to ultralow temperatures
    (2014) Clauß, Conrad; Dressel, Martin (Prof. Dr.)
    This thesis presents a novel technical realization to perform electron paramagnetic resonance (EPR) based on superconducting coplanar waveguides (CPWs) and superconducting CPW resonators. This technique allows for the investigation of magnetic properties of the material under study at basically any arbitrary frequency. The compact design radically facilitates the implementation into dilution refrigerators to probe the samples at temperatures in the milli Kelvin regime. The working principle of the devices is explained and further substantiated by analytical calculations and 3D-electromagnetic (EM) simulations of the microwave EM fields of the given chip structures. The proof of principle was demonstrated on an organic radical with spin 1/2 and on a ruby single crystal with S=3/2, as a more complex spin system. The technique was then utilized to characterize a Gd-based single-ion magnet and to investigate the magnetic properties of the ground states of a heavy-fermion metal. Both materials were studied in detail at temperatures as low as 40 mK, far below the typical low-temperature limit of conventional EPR equipment at around 1 K. The results of the heavy-fermion compound reveal intriguing behavior of the spin-relaxation mechanisms and local magnetic fields at the lowest achievable temperatures and at the phase transitions and crossover regimes of the phase diagram. The thesis is a pioneering work outlining the great potential regarding the range of applicability of the introduced technique and provides a starting point for future improvements and further functional enhancements.