Neutron diffraction study of magnetic ordering in quasi-1D S=1 Haldane chain compounds

Materials with (S=1) Ni2+ ions in quasi-one-dimensional spin-chains are of great interest because of the formation of a Haldane gap in the ground state. The compounds PbM2Ni6Te3O18 (M = Fe, Co, Zn) are new systems with hexagonal structure and quasi-1D chains formed by Ni2+. The M2+ ions provide additional spins whit S=2, S=3/2 and S=0 for M=Fe, Co and Zn respectively, tuning the exchange interactions and proving new degree of freedom. Recently our group has investigated another member of the family with M=Cd, using elastic and inelastic neutron scattering. The obtained result revealed a complex AFM ordering with propagation vector k=(1/3 1/3 0), which is different from the simple collinear k=0 magnetic structure found in M=Mn compound. To understand the role of M ions in the magnetic structure stability and the magnetic exchange interactions, we propose to investigate magnetic orders in the M=Fe, Co and Zn members, using WISH diffractometer. The obtained information will also help to analysis spin waves in these compounds, which are going to be investigated using inelastic neutron scattering.