Spin‐lattice relaxation of spin‐½ nuclei in solids containing diluted paramagnetic impurity centers. III. Dynamic polarization of nuclear spin system by nuclear orientation via electron spin locking

Abstract

AbstractDynamic nuclear polarization of nuclei by means of paramagnetic electron spin locking (Hartmann‐Hahn cross‐polarization between paramagnetic electrons and nuclei, or NOVEL) is discussed. The theory is demonstrated by experiments executed at 2.4 and 9.6 GHz on a natural type Ib diamond. It is shown that the 13C polarization rate is independent of the microwave frequency, in agreement with theory. NOVEL polarization takes place only while the spin‐locking pulse is on. The rate at which the nuclei are polarized is proportional to the electron polarization in the rotating frame. Therefore, the length of the spin‐locking pulse is limited by the value of T1ρ(e), and because T1ρ(e) ≪ T1(e) for diamond the effective NOVEL polarization rate of 13C nuclei is usually relatively low. A comparison between the relative effectiveness of 13C polarization rates between NOVEL and the solid‐state effect is made for high and low paramagnetic impurity concentrations. The dependence of the 13C polarization rate on the paramagnetic impurity concentration has been determined for a suite of natural diamonds. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 44–49, 2003.