Neutron diffraction study of magnetic structures in TbNiAl

A single crystal of TbNiAl has been studied by neutron diffraction and magnetization measurements. Terbium magnetic moments are aligned along the c-axis over the whole temperature range below T-N = 44.6 K, A change of the propagation and magnitude of one-third of the moments occurs at T-1 = 23.5 K. Below T-1, moments at (x,0,1/2) and ((x) over bar,(x) over bar,1/2) propagate with k = (1/2,0,1/2), while moments at (0,x,1/2) propagate with k' = (0,1/2,1/2) or k '' = (-1/2,1/2,1/2). All moments have the same magnitude. Between T-1 and T-N, all moments propagate with the same propagation vector k, but moments at (0,x,1/2) are significantly reduced. A metamagnetic transition occurs in a field of 0.4 T applied along the c-axis.