Nuclear magnetic resonance in solid and liquid manganese

Nuclear-magnetic-resonance measurements at elevated temperatures are described for the four solid allotropic forms and the liquid state of manganese. Knight-shift (K) data extend from 300 K (α-Mn) to 1575 K (liquid) and spin-lattice relaxation rates (1T₁) were measured from 1050 K (β-Mn) to 1570 K (liquid). Knight shifts in α- and β-Mn 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 β-Mn allowed determination of K for both sites. At 1200 K, KI=(+0.030±0.005)% and KII=(-0.720±0.005)% for type-I and type-II sites, respectively. In contrast to α- and β-Mn, small changes of K and 1T₁ at the high-temperature transitions indicate that the d-spin magnetization is only weakly influenced by crystal structure changes at high temperature and by melting. The observed shifts are (-0.690 ±{} 0.005)% (γ-Mn at 1400 K), (-0.828 ±{} 0.005)% (δ-Mn at 1450 K), and (-0.821 ±{} 0.005)% (liquid Mn at 1525 K). With the exception of shifts for type-I and type-II sites in α-Mn, all shifts tend toward more negative values with increasing temperature within a single phase region. Above 1375 K, (T₁T)^-1 is essentially constant in γ-, δ-, and liquid Mn and equal to 14.5 ±{} 0.7 (secK)^-1. Decomposition of the d-spin susceptibility using a K vs χ analysis led to orbital and spin susceptibilities of (0.141 ±{} 0.017) ×{} 10^-3 and (0.451 ±{} 0.017) ×{} 10^-3 emu/mole for γ-Mn, and similar values were obtained for δ- and liquid Mn. The spin susceptibility is enhanced by roughly a factor of 25, and the d-spin hyperfine field (-223 ±{} 22 kOeμB) is due mainly to spin-polarized conduction-electron hyperfine fields originating on neighboring atoms.