Regensburg 2013 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 42: New Instruments and Methods
CPP 42.5: Vortrag
Donnerstag, 14. März 2013, 12:30–12:45, H39
Larmor precession in ultralow magnetic fields detected by Field Cycling NMR — •Benjamin Kresse — Institut für Festkörperphysik, TU Darmstadt, Hochschulstr. 6, 64289 Darmstadt
Field Cycling (FC) relaxometry is a powerful tool to measure the microscopic dynamics at a wide range of Larmor frequencies. Typically, the highest accessible magnetic field of about 1 Tesla is limited by the power of the magnet, while the low frequency limit is the noise of the current source. The present work deals with experiments in the low frequency range.
For reaching low magnetic fields in an FC experiment it is important to (i) compensate the earth field, (ii) avoid a zero field overshoot during the fast field switch from high to low field, (iii) stabilize the low field and (iv) measure the low field at the sample position.
Our way to solve these problems is to implement a set of five independently controlled coils into our home built FC magnet. This setup allows us to perform non-adiabatic field switch down to a low evolution field which is controlled by an active fluctuation compensation. In a series of test experiments the lowest stable magnetic field we reached and measured directly by Larmor precession of protons in a water sample was about 0.3 microTesla corresponding to ν0(1H) = 12 Hz [B. Kresse, A. Privalov, F. Fujara / Solid State Nuclear Magnetic Resonance 40 (2011) 134-137]. With this setup it is also possible to measure T1 and the evolution field combined in one and the same measurement.