Nuclear magnetic and quadrupole resonance in metallic powders in the presence of strong quadrupole interaction: Rhenium metal

The nuclear-magnetic-resonance and nuclear-quadrupole-resonance (NQR-NMR) spectra of 187Re and 185Re in a powder of rhenium metal were measured in the temperature range 5--10 K both in zero field and with an external magnetic field. The zero-field NQR spectrum is severely broadened by a nonuniform distribution of quadrupole interactions. The average quadrupole coupling frequencies measured at 5 K are, for the two isotopes, ν/sub Q/ = 39 +- 0.2 MHz (187Re) and ν/sub Q/ = 40.8 +- 0.3 MHz (185Re). The spectra obtained in the presence of an external magnetic field can be interpreted satisfactorily in terms of transitions among the eigenstates of the full Hamiltonian (Zeeman plus quadrupolar). Measurements of relaxation rates yield T1T = 0.03 sK, indicating a relaxation mechanism driven by the hyperfine interaction with the conduction electrons. The feasibility of NQR-NMR studies in small metal particles in the presence of strong inhomogeneous quadrupole interactions is assessed