Nuclear magnetic resonance in solid and liquid manganese

Abstract

Nuclear-magnetic-resonance measurements at elevated temperatures are described for the four solid allotropic forms and the liquid state of manganese. Knight-shift ($\mathcal{K}$) data extend from 300 K ($\ensuremath{\alpha}\ensuremath{-}\mathrm{M}\mathrm{n}$) to 1575 K (liquid) and spin-lattice relaxation rates ($\frac{1}{{T}_{1}}$) were measured from 1050 K ($\ensuremath{\beta}\ensuremath{-}\mathrm{M}\mathrm{n}$) to 1570 K (liquid). Knight shifts in $\ensuremath{\alpha}\ensuremath{-}$ and $\ensuremath{\beta}\ensuremath{-}\mathrm{M}\mathrm{n}$ exhibit a strong dependence on crystallographic site reflecting a highly nonuniform distribution of paramagnetism within the unit cell. Motional narrowing of the splitting between the two inequivalent sites in $\ensuremath{\beta}\ensuremath{-}\mathrm{M}\mathrm{n}$ allowed determination of $\mathcal{K}$ for both sites. At 1200 K, ${\mathcal{K}}_{\mathrm{I}}=(+0.030\ifmmode\pm\else\textpm\fi{}0.005)%$ and ${\mathcal{K}}_{\mathrm{II}}=(\ensuremath{-}0.720\ifmmode\pm\else\textpm\fi{}0.005)%$ for type-I and type-II sites, respectively. In contrast to $\ensuremath{\alpha}\ensuremath{-}$ and $\ensuremath{\beta}\ensuremath{-}\mathrm{M}\mathrm{n}$, small changes of $\mathcal{K}$ and $\frac{1}{{T}_{1}}$ at the high-temperature transitions indicate that the $d\ensuremath{-}\mathrm{s}\mathrm{p}\mathrm{i}\mathrm{n}$ magnetization is only weakly influenced by crystal structure changes at high temperature and by melting. The observed shifts are (-0.690 \ifmmode\pm\else\textpm\fi{} 0.005)% ($\ensuremath{\gamma}\ensuremath{-}\mathrm{M}\mathrm{n}$ at 1400 K), (-0.828 \ifmmode\pm\else\textpm\fi{} 0.005)% ($\ensuremath{\delta}\ensuremath{-}\mathrm{M}\mathrm{n}$ at 1450 K), and (-0.821 \ifmmode\pm\else\textpm\fi{} 0.005)% (liquid Mn at 1525 K). With the exception of shifts for type-I and type-II sites in $\ensuremath{\alpha}\ensuremath{-}\mathrm{M}\mathrm{n}$, all shifts tend toward more negative values with increasing temperature within a single phase region. Above 1375 K, ${({T}_{1}T)}^{\ensuremath{-}1}$ is essentially constant in $\ensuremath{\gamma}\ensuremath{-}$, $\ensuremath{\delta}\ensuremath{-}$, and liquid Mn and equal to 14.5 \ifmmode\pm\else\textpm\fi{} 0.7 ${(\mathrm{sec}\mathrm{K})}^{\ensuremath{-}1}$. Decomposition of the $d$-spin susceptibility using a $\mathcal{K}$ vs $\ensuremath{\chi}$ analysis led to orbital and spin susceptibilities of (0.141 \ifmmode\pm\else\textpm\fi{} 0.017) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ and (0.451 \ifmmode\pm\else\textpm\fi{} 0.017) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ emu/mole for $\ensuremath{\gamma}\ensuremath{-}\mathrm{M}\mathrm{n}$, and similar values were obtained for $\ensuremath{\delta}\ensuremath{-}$ and liquid Mn. The spin susceptibility is enhanced by roughly a factor of 25, and the $d$-spin hyperfine field (-223 \ifmmode\pm\else\textpm\fi{} 22 $\frac{\mathrm{kOe}}{{\ensuremath{\mu}}_{B}}$) is due mainly to spin-polarized conduction-electron hyperfine fields originating on neighboring atoms.