Recent developments and new trends in NMR on oriented nuclei

Recent developments in nuclear magnetic resonance on oriented nuclei (NMR-ON) are reviewed with the following main topics: (i) Measurement of magnetic moments. In this context the resonance shift of NMR-ON resonances with an external magnetic field is discussed critically. (ii) Resonance techniques for the measurement of electric quadrupole moments. It is shown that - with hcp-Co as host matrix - the techniques QI-NMR-ON (quadrupole-interaction-resolved NMR-ON) and MAPON (modulated adiabatic passage on oriented nuclei) have a tremendous potential for the measurement of quadrupole moments of radioactive nuclei. Data are presented for medium (Zr, Nb) and heavy elements (Ir, Pt, Au, Hg). With results on the 11/2(-) isomers in Au it is shown that MAPON yields highly precise quadrupole moments of states with half-lives of the order of seconds, for which no other technique with comparable precision exists up to now. In the case of Nb-90 it is demonstrated that MAPON allows also the measurement of very small quadrupole moments with high precision. (iii) Electric field gradients in cubic Fe, fee-Co and Ni. MAPON experiments show a strong magnetic-field dependence of the ''effective'' quadrupole interaction; the implications are discussed. (iv) beta-decay-induced lattice site change identified by a double-resonance NMR-ON measurement. The resulting change of the hyperfine interaction has severe consequences for the interpretation of time-integral and even time-differential nuclear orientation measurements on nuclei far off stability. (v) Spin-lattice relaxation for nuclei on non-substitutional lattice sites. Recent experiments support the global character of the spin-lattice relaxation, in contrast to the local character of the static magnetic hyperfine interaction. (vi) Magnetic-field dependence of the spin-lattice relaxation. Recent experiments with hcp-Co as host lattice strongly support the so-called enhancement factor model and disfavour the one-, two- or three-magnon processes postulated in the literature.