INCOMMENSURATE ANTIFERROMAGNETIC STRUCTURES IN NDIN3

Among the AuCu3-type RIn3 series where R is a rare earth, the NdIn3 compound presents a complex magnetic phase diagram. In this compound, which orders antiferromagnetically at T(N) = 5.9 K, three magnetic phases are separated by two sharp first-order transitions. The phase diagrams, determined for the main crystallographic directions, by magnetization measurements in fields up to 7 T show a strong dependence of the transition temperatures. In order to determine the actual magnetic structures in NdIn3, a neutron diffraction experiment has been performed on a single crystal under magnetic field. It shows that the magnetic structures are collinear (single q) with the magnetic moments aligned along the fourfold axis. They clearly evidence the existence of two incommensurate phases with q = (1/2, 1/2, tau): for T(N) greater-than-or-equal-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 the structure squares up. Below 4.7 K the q = (1/2, 1/2, 0) commensurate structure is stabilized.