Temperature Dependence of the Hyperfine Field and Hyperfine Coupling Constant of Iron

Abstract

The hyperfine field of $^{57}\mathrm{Fe}$ in natural iron has been measured by continuous-wave NMR in the temperature range 4.2-400 \ifmmode^\circ\else\textdegree\fi{}K. The measurements below 32 \ifmmode^\circ\else\textdegree\fi{}K follow a ${T}^{\frac{3}{2}}$ law and are in good agreement with the magnetization data. A single extra term in ${T}^{\frac{5}{2}}$ is sufficient to fit the hyperfine-field measurements, reduced to zero spin-wave gap, between 32 and 400 \ifmmode^\circ\else\textdegree\fi{}K. The hyperfine coupling constant is temperature dependent, despite the agreement in the ${T}^{\frac{3}{2}}$ term found by magnetization and hyperfine field measurements, with the form ${A}_{T}=1\ensuremath{-}6.58\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}{T}^{\frac{5}{2}}+8.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}{T}^{\frac{7}{2}}$.