Origin of field-induced discontinuous phase transitions in Nd2Fe17

Abstract

Magnetic properties of a trigonal ferromagnet $\mathrm{N}{\mathrm{d}}_{2}\mathrm{F}{\mathrm{e}}_{17}$ have been studied on single crystals in steady (14 T) and pulsed (32 T) magnetic fields. The easy-magnetization direction lies close to the [120] axis, deviating from the basal plane by $2.{9}^{\ensuremath{\circ}}$ (at $T=5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$). Of particular interest is the low-temperature magnetization process along the high-symmetry axis [001], which is the hard direction. This process is discontinuous and involves two first-order phase transitions (FOMPs). One of them (at 20 T) is a symmetry FOMP similar to that observed in $\mathrm{S}{\mathrm{m}}_{2}\mathrm{F}{\mathrm{e}}_{17}$. The second transition (at 10.4 T) is unusual: as the magnetization turns abruptly toward the applied field, it also changes its azimuthal orientation (the angle $\ensuremath{\varphi}$) by ${60}^{\ensuremath{\circ}}$. Both transitions can be reasonably accounted for by the presence of a significant sixth-order trigonal anisotropy term.