Field-induced transformations of the spin ordering in Nd2CuO4

Abstract

Using elastic neutron scattering, we show first that at zero field Nd 2 CuO 4 undergoes successive magnetic phase transitions associated with the Cu ++ spins. A phase I with La 2 NiO 4 magnetic type structure is stabilized between T N ≈ 250 K and T 1≈ 80 K and a phase II with a La 2 CuO 4 magnetic type structure is formed between T 1 and T 2≈ 30 K. Below T 2 a phase III with a magnetic structure similar to that of phase I, is stabilized down to the lowest temperatures. When a small magnetic field, up to about 2 Tesla, is continuously applied perpendicular to the tetragonal axis along (1,−1,0), the magnetic reflections ( 1 2 , 1 2 ,l) with odd integers l continuously vanish in the stability region of phases I and III, while the intensity of those with even integers l increases. However in the region of phase II the opposite occurs: even l reflections continuously vanish and odd l reflections are enhanced. The results indicate that at relatively small field of about 0.7 Tesla, a single magnetic domain with collinear spins is stabilized. Further, detailed studies of the reversibility of these transformations upon the applied field show no significant hysteresis, suggestive of a continuous transformation from non collinear spins structures at zero field into their collinear analogues at high field.