Neutron diffraction study of magnetic ordering in RNiAl compounds

We studied magnetic ordering in RNiAl (R = Pr, Nd, Tb, Dy, Ho and Er) compounds by neutron diffraction. All observed magnetic structures have a common propagation vector k = (0.5, 0, q), commensurate (q = 0.5) for heavy rare earths (R = Tb, Dy, Ho and Er) and incommensurate in PrNiAl (q = 0.41) and NdNiAl (q = 0.46) with q temperature invariable down to 1.8 K. The antiferromagnetic (AF) ground-state phases have the rare-earth magnetic moments lying in the basal plane for R = Pr, Nd, Er and oriented along the c-axis in TbNiAl. The canted structures in DyNiAl and HoNiAl are combinations of the AF coupled basal-plane components and the c-axis ferromagnetic ones. The latter three materials (R = Tb, Dy, Ho) exhibit a magnetic phase transition in the ordered state connected with quite a complex moment re-arrangement.