Magnetic structure of DyN: A Dy161 Mössbauer study

Conventional magnetometry yields a low temperature bulk magnetic moment of about $4\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\phantom{{\ensuremath{\mu}}_{\mathrm{B}}\mathrm{D}{\mathrm{y}}³⁺}\phantom{\rule{0.0pt}{0ex}}\mathrm{D}{\mathrm{y}}³⁺$ in an applied field of ${\ensuremath{\mu}}₀H=9\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.28em}{0ex}}\mathrm{T}$ for thin and thick dysprosium nitride (DyN) films. This is significantly lower than the maximum possible value of $10\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\phantom{10\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}\mathrm{D}{\mathrm{y}}³⁺}\phantom{\rule{0.0pt}{0ex}}\mathrm{D}{\mathrm{y}}³⁺.$ Ion-assisted deposition was used to grow 5.7-\ensuremath{\mu}m-thick rare earth nitride DyN films on organic Kapton\textregistered{} substrates. $¹⁶¹\mathrm{Dy}$ M\"ossbauer spectroscopy (with its time scale on the order of nanoseconds) indicates thermal relaxation between fully stretched $\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ levels of a low-lying Kramers doublet, which is inconsistent with the $\mathrm{D}{\mathrm{y}}³⁺$ site's ideal cubic symmetry. However, a small tetragonal distortion $[\ensuremath{\epsilon}\ensuremath{\approx}\ensuremath{-}0.024(10)]$ observed using x-ray powder diffraction is compatible with an additional rank 2 crystal field term, ${B}₂⁰\ensuremath{\approx}\ensuremath{-}1.0(4)\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, approaching the magnitude estimated to bring this about. The observed magnetic behavior can then be described using a two-level, molecular field model with ${\ensuremath{\theta}}_{\mathrm{C}}$ set to $\ensuremath{\approx}6--8\phantom{\rule{0.16em}{0ex}}\mathrm{K},$ which is substantially smaller than the accepted ordering temperature of ${T}_{\mathrm{C}}\ensuremath{\approx}17--26\phantom{\rule{0.16em}{0ex}}\mathrm{K}$.