A new modification of nickel selenite NiSeO3—crystal structure and magnetic properties

• Published in: Journal of physics. Condensed matter 2007-05, Vol.19 (19), p.196203-196203 (14)
• Main Authors: Miljak, M, Becker, R, Herak, M, Prester, M, Milat, O, Johnsson, M, Berger, H
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Inorganic compounds; Magnetic properties and materials; Physics; Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.); Structure of solids and liquids; crystallography; Structure of specific crystalline solids
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/19/19/196203

The crystal structure of a new modification of NiSeO3 is described together with its magnetic properties. The new polymorph crystallizes in the monoclinic system, space group C 2/c, with unit cell parameters a = 15.4965(7) A, b = 9.8250(4) A, c = 14.7278(8) A, beta = 110.610(4) deg and Z = 8. The crystal structure was solved from single crystal data, R = 0.0252. The structure can be considered as being layered along the bc-plane with [NiO6] octahedra arranged into two sub-groups. The layers are further connected to adjacent layers via groups of two edge-sharing [NiO6] octahedra. The Ni octahedra are tilted and are either edge or corner sharing, giving rise to two different Ni-Ni interactions. The lone pairs of Se4+ occupy non-bonding regions of tunnels along [001] and [010]. The complexity of the crystal structure is also reflected in the complex low-temperature magnetic state. An antiferromagnetic-like transition was observed at Ttr = 14.4 K. A possible structural rearrangement closely above Ttr complicates the details of the low-temperature state. The antiferromagnetic-like transition disagrees with the features of a three-dimensional (3D) Neel antiferromagnetic ordering. This is mostly because of the fact that the assumed bulk easy-axis susceptibility at the lowest temperature remains at high paramagnetic value. The consequences of the complex structure on basic magnetic parameters, zero-field splitting energy D and exchange coupling J, and accordingly on the magnetic properties, are discussed.