INCOMMENSURATE ANTIFERROMAGNETIC STRUCTURES IN NDIN3

Among the AuCu3-type RIn3 series where R is a rare earth, the NdIn3 co mpound presents a complex magnetic phase diagram. In this compound, wh ich orders antiferromagnetically at T(N) = 5.9 K, three magnetic phase s are separated by two sharp first-order transitions. The phase diagra ms, determined for the main crystallographic directions, by magnetizat ion measurements in fields up to 7 T show a strong dependence of the t ransition temperatures. In order to determine the actual magnetic stru ctures in NdIn3, a neutron diffraction experiment has been performed o n a single crystal under magnetic field. It shows that the magnetic st ructures are collinear (single q) with the magnetic moments aligned al ong the fourfold axis. They clearly evidence the existence of two inco mmensurate phases with q = (1/2, 1/2, tau): for T(N) greater-than-or-e qual-to T > 5.5 K, tau1 almost-equal-to 0.037 2pi/a and the structure is sine-wave modulated, for 5.5 K > T> 4.7 K, tau2 = 0.017 2pi/a and t he structure squares up. Below 4.7 K the q = (1/2, 1/2, 0) commensurat e structure is stabilized.