NMR ofN14in the Paramagnetic State of Uranium Mononitride

摘要: Uranium mononitride (UN) has the NaCl-type structure, is a good conductor of electricity, antiferromagnetic (type I) below \ensuremath{\sim}53\ifmmode^\circ\else\textdegree\fi{}K, and obeys Curie-Weiss law in paramagnetic state temperature range 77-300\ifmmode^\circ\else\textdegree\fi{}K. A continuous-wave NMR study was carried out on $^{14}\mathrm{N}$ this applied magnetic fields 6340-13 000 Oe by use Varian V-4210A spectrometer. The signals were detected only dispersion mode using high modulations rf fields. positive temperature-dependent Knight shift can be represented $K={K}_{0}+\ensuremath{\alpha}{\ensuremath{\chi}}_{M}$, where ${K}_{0}=\ensuremath{-}(31.5\ifmmode\pm\else\textpm\fi{}3.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ different from shift, + (10.7\ifmmode\pm\else\textpm\fi{}1.5)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$, isostructural ThN. difference probably due to some temperature-independent susceptibility \ensuremath{\sim}${10}^{\ensuremath{-}3}$ cgs. coefficient $\ensuremath{\alpha}$ 4.20+0.25 (when ${\ensuremath{\chi}}_{M}$ cgs units), which practically same value as for other uranium compounds; analyzed assumption ${\mathrm{U}}^{+4}$ ions ($5{f}^{2}$ configuration) recent 0.876 conduction electrons per atom. In model with uniform conduction-electron polarization, an exchange constant ${J}_{\mathrm{sf}}$ - (1.0\ifmmode\pm\else\textpm\fi{}0.2) eV obtained that sign lanthanides, but about one order magnitude larger; variation larger extent $5f$ electronic functions. Ruderman-Kittel-Kasuya-Yosida (RKKY) model, $s\ensuremath{-}f$ coupling $\ensuremath{\Gamma}=\ensuremath{-}460$ ${\mathrm{\AA{}}}^{3}$ again negative, eight times higher than $|\ensuremath{\Gamma}|$ Curie ($\ensuremath{\theta}\ensuremath{\simeq}\ensuremath{-}320\ifmmode^\circ\else\textdegree\fi{}$K) contribution resistivity. T mainly sensitivity RKKY sums, also may simple used. compounds, have ordered state, indication nonapplicability analysis shifts. linewidth UN depends field. terms quadrupole interaction (similar contributes total ThN) proportional $\frac{{H}_{0}}{(T\ensuremath{-}\ensuremath{\theta})}$ UP absent). These results are compared those lanthanide nitrides compounds state.