MICTOMAGNETIC BEHAVIOR OF CENI0.84SN2 - A NEUTRON-DIFFRACTION AND MAGNETIC STUDY

The magnetic properties of the orthorhombic (Cmcm) antiferromagnetic c ompound of nominal composition CeNiSn2.1 were studied by magnetisation measurements and neutron diffraction. The refinement of the nuclear s tructure shows a Ni deficiency, leading to the formula CeNi0.840(4)Sn- 2. At 1.5 K two magnetic phases coexist in equal amounts. One of these is ferromagnetic q(1) = 0 with T-C = 3 K. The other phase is an antif erromagnetic modulated phase (antiphase domain type with two amplitude s) with T-N = 4.0 K. Its magnetic ordering can be described by two pro pagation vectors q(2) = (010) (C-P magnetic lattice) and q(3) = 1/36. The ordered magnetic moment value at 1.5 K in both phases is 2.0 mu(B )/Ce atom and points to the same direction along c. Above 2 K the wave vector q(3), becomes incommensurate with the crystal lattice. The obs ervation of two magnetic phases is attributed to the occurrence of con centration fluctuations associated with the Ni deficiency.