Nuclear Magnetic Resonance in the Paramagnetic States of MnO,α−MnS, andα−MnSe

The ${\mathrm{Mn}}^{55}$ and ${\mathrm{Se}}^{77}$ NMR have been observed in the paramagnetic states of the antiferromagnetic compounds MnO, $\alpha -\mathrm{M}\mathrm{n}\mathrm{S}$, and $\alpha -\mathrm{M}\mathrm{n}\mathrm{S}\mathrm{e}$. The ${\mathrm{Mn}}^{55}$ and ${\mathrm{Se}}^{77}$ NMR frequency shifts were found to be temperature-dependent and proportional to the magnetic susceptibility. From an analysis of the NMR frequency shift and magnetic-susceptibility data, the following hyperfine coupling constants were determined: $A^{55}\left(\mathrm{MnO}\right)=-(81.5\mathrm{}\pm 2.5)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $A^{55}(\alpha -\mathrm{M}\mathrm{n}\mathrm{S})=-(71.8\mathrm{}\pm 5.3)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $A^{55}(\alpha -\mathrm{M}\mathrm{n}\mathrm{S}\mathrm{e})=-(67.0\mathrm{}\pm 4.5)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and $A^{77}(\alpha -\mathrm{M}\mathrm{n}\mathrm{S}\mathrm{e})=+(7.2\mathrm{}\pm 0.6)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. Additional information regarding the Néel temperatures of $\alpha -\mathrm{M}\mathrm{n}\mathrm{S}$ and $\alpha -\mathrm{M}\mathrm{n}\mathrm{S}\mathrm{e}$ was obtained by studying the temperature dependence of the ${\mathrm{Mn}}^{55}$ NMR intensity with the result $T_N(\alpha -\mathrm{M}\mathrm{n}\mathrm{S})=(147\mathrm{}\pm 1)$°K and $T_N(\alpha -\mathrm{M}\mathrm{n}\mathrm{S}\mathrm{e})\simeq 150$°K. The experimental ${\mathrm{Mn}}^{55}$ and ${\mathrm{Se}}^{77}$ NMR linewidths were found to be in agreement with predictions based upon the theory of exchange-narrowed hyperfine-broadened NMR linewidths in paramagnetic insulators.