Revealing the hidden hyperfine interactions in ε-iron

Herein, evidence for the long-sought finite hyperfine interaction in the high-pressure hexagonal close-packed $\ensuremath{\epsilon}$-iron is gained through synchrotron radiation perturbed angular correlation spectroscopy. This method yields an energy splitting of $3.5(5)\phantom{\rule{4.pt}{0ex}}\text{neV}$ between the ${m}_{{I}_{\text{e}}}=\ifmmode\pm\else\textpm\fi{}1/2$ and ${m}_{{I}_{\text{e}}}=\ifmmode\pm\else\textpm\fi{}3/2$ nuclear sublevels of the iron-57 $14.412\text{-keV}$ nuclear excited state at $30(1)\phantom{\rule{4.pt}{0ex}}\text{GPa}$ and room temperature. This energy splitting is related to a nuclear quadrupole hyperfine interaction with an electric field gradient of $eq=1.2(2)\ifmmode\times\else\texttimes\fi{}{10}^{16}{\phantom{\rule{0.16em}{0ex}}\mathrm{V}/\mathrm{cm}}^{2}$. However, there is still a possibility that the splitting of the iron-57 nuclear levels is related to a modest magnetic hyperfine interaction of ca. $0.40(5)\phantom{\rule{4.pt}{0ex}}\text{T}$.