The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Dissertation for the degree Doctor of Science in Technology to be presented with due permission for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 24th of November, 2000, at 12 noon.
Overview in PDF format (ISBN 951-22-5214-7) [780 KB]
Dissertation is also available in print (ISBN 951-22-5208-2)
This thesis presents the results of experiments studying nuclear magnetism, superconductivity and their mutual interaction in rhodium at ultralow temperatures with high nuclear polarizations. The experiments were performed with a new cooling apparatus particularly designed for such measurements.
The highest nuclear polarizations reached were p = 0.95 and the lowest achieved temperature of the nuclear spin system was below 100 pK. The measured susceptibility data showed a clear antiferromagnetic tendency of the nuclear spin system, but no indication of a magnetically ordered state was observed.
Multiple spin flips, where a single photon flips several nuclei were observed. The double-spin-flip resonance was observed at positive and for the first time also at negative spin temperatures. The behavior of the resonance fitted the theoretical expectations very well and its frequency shift gives direct information of the mutual interactions between the nuclear spins. A possible trace of the triple-spin-flip peak was also detected.
Because of the rare properties of rhodium, where the critical field of superconductivity is considerably lower than the local field of the nuclei, experiments could be performed with polarized nuclei also in the superconducting state of the electron system. The measurements could thus be extended to a completely new regime, where polarized nuclei are embedded in a coherent conduction electron system. The spin-lattice relaxation time was found to be always longer in the superconducting state as compared to the normal state. Additionally in the superconducting state the relaxation time displayed an unexpectedly strong polarization dependence.
This thesis consists of an overview and of the following 8 publications:
Keywords: rhodium, nuclear magnetism, superconductivity, spin-lattice relaxation
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© 2000 Helsinki University of Technology