Magnetic ordering in silicon defect NdSi compounds studied by neutron diffraction and magnetic measurements

Abstract

Earlier investigations had indicated the presence of a compound (of unknown structure) with the composition Nd 3Si 4. Our neutron diffraction data show that the compound crystallizes in a novel type of structure related to the CrB and α-GdSi 2 structure types. The structure is orthorhombic and comprises two neodymium sites and three silicon sites. It is a defect structure in which about 50% of one of the silicon sites is unoccupied, leading to the composition Nd 2Si 3–5 with σ = 0.5. The compound orders ferromagnetically below T c = 80 K and the neodymium moments are oriented along the c axis. The experimental results obtained for Nd 2Si 3−5 are discussed together with the defect structures of the α-GdSi 2 type observed for NdSi x in the range 1.75⩽ x⩽1.85. The distribution of the vacancies changes substantially within this range and the magnetic ordering changes with increasing x from ferromagnetic to antiferromagnetic.