Dynamic Nuclear Polarization by Thermal Mixing Under Partial Saturation
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We describe a low-temperature thermodynamic model for dynamic nuclear polarization (DNP) via continuous-wave partial saturation of electron spin resonance (ESR) lines that are both homogeneously and inhomogeneously broadened. It is a variant of a reasoning proposed by Borghini, which in turn used Redfield’s thermodynamic treatment of saturation. Our variant is furthermore based on Provotorov’s insight that under partial saturation of a coupled-spin system two distinct spin temperatures should appear in a thermodynamical theory. We apply our model to DNP results obtained at a temperature of 1.2 K and in magnetic fields of 3.35 and 5 T on 1-13C labeled sodium acetate dissolved in a frozen D2O/ethanol-d6 solution doped with the free radical TEMPO.
KeywordsElectron Spin Resonance Microwave Power Lattice Relaxation Dynamic Nuclear Polarization Electron Spin Resonance Line
The authors wish to acknowledge Dr. Ben van den Brandt, Dr. J. A. (Ton) Konter and Dr. Patrick Hautle of the Paul Scherrer Institute for the design and construction of the DNP cryostat. This work was supported by the Swiss National Science Foundation (Grants No. 200021-109479 and PP00P2_133562). Part of the experimental work was done while the authors were in the Laboratory of the Physics of Nanostructured Materials (LPMN) of the EPFL. Sami Jannin additionally acknowledges support from Prof. Geoffrey Bodenhausen, the Commission pour la Technologie et l’Innovation (CTI Grant 9991.1 PFIW-IW), and SNF (Grant No. 200020-124694).
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