Lattice symmetry of the spiral spin-density-wave state inγ−Feprecipitates in Cu

Abstract

Lattice symmetry of $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ in a spiral spin-density-wave (SDW) state was studied by neutron scattering experiments under uniaxial stress. If we express a wave vector of the spiral SDW as ${\mathbf{q}}_{2}={\mathbf{Q}}_{\mathrm{AF}}+{\mathbf{Q}}_{\mathrm{md}}$, where ${\mathbf{Q}}_{\mathrm{AF}}=(1,0,0)(2\ensuremath{\pi}∕a)$ and ${\mathbf{Q}}_{\mathrm{md}}=(0,\ensuremath{\xi},0)(2\ensuremath{\pi}∕a)$, the volume fraction of $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ precipitates with the ${\mathbf{Q}}_{\mathrm{md}}$ vector parallel to uniaxial stress increasing and that with the ${\mathbf{Q}}_{\mathrm{AF}}$ vector decreasing under uniaxial stress, indicating that an fcc lattice contracts along the direction parallel to ${\mathbf{Q}}_{\mathrm{md}}$ and expands along the ${\mathbf{Q}}_{\mathrm{AF}}$ direction below the N\'eel temperature. The magnitude of the lattice distortion is estimated to be of the order of ${10}^{\ensuremath{-}4}$, which would not suffice to explain the discrepancies between the experimental results and the first principles calculations assuming the ideal cubic lattice. Similarities of the lattice symmetry with CuMn spin-glass alloys are discussed.