Ordering wave vectors of metamagnetic states inHoNi2B2C:One dimension is not enough

Abstract

Elastic neutron-diffraction measurements have been preformed in each of the metamagnetic states of ${\mathrm{HoNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ for an applied field applied in the tetragonal basal plane making an angle of approximately $15\ifmmode^\circ\else\textdegree\fi{}$ with the $[110]$ axis. Whereas these data are in excellent quantitative agreement with earlier thermodynamic studies of the ${H}_{\mathrm{app}}\ensuremath{-}\ensuremath{\theta}$ phase diagram of ${\mathrm{HoNi}}_{2}{\mathrm{B}}_{2}\mathrm{C},$ the magnetic wave vector of the metamagnetic state, $\ensuremath{\approx}{4/7a}^{\ensuremath{\star}},$ is in stark contradiction with the predictions of two, one-dimensional theoretical models developed for this system. On the other hand, simple energetic arguments which are consistent with the existence of the ${a}^{\ensuremath{\star}}$ phase are presented.