NMR field-cycling at ultralow magnetic fields.

ABSTRACT

The paper describes some significant technical improvements of a home built NMR field cycling relaxometer [O. Lips, A. Privalov, S. Dvinskikh, F. Fujara, J. Magn. Reson. 149 (2001) 22-28] now allowing for fast switching of polarization fields (up to more than 1T) to evolution fields down to the sub-µT range. The most important instrumental details such as the description of an involved 3-dimensional resistive coil setup are given. Fields below about 5 µT can only be stabilized by incorporation of an active field drift and fluctuation compensation tool. In this way, the smallest 1H Larmor frequency obtained and measured so far has been 12 Hz.