Hydrothermal Synthesis in the System Ni(OH)<sub>2</sub>−NiSO<sub>4</sub>: Nuclear and Magnetic Structures and Magnetic Properties of Ni<sub>3</sub>(OH)<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>
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We present the synthesis, characterization by DT-TGA and IR, single crystal X-ray nuclear structure at 300 K, nuclear and magnetic structure from neutron powder diffraction on a deuterated sample at 1.4 K, and magnetic properties as a function of temperature and magnetic field of Ni3(OH)2(SO4)2(H2O)2. The structure is formed of chains, parallel to the c-axis, of edge-sharing Ni(1)O6 octahedra, connected by the corners of Ni(2)O6 octahedra to form corrugated sheets along the bc-plane. The sheets are connected to one another by the sulfate groups to form the 3D network. The magnetic properties measured by ac and dc magnetization, isothermal magnetization at 2 K, and heat capacity are characterized by a transition from a paramagnet (C = 3.954 emu K/mol and θ = −31 K) to a canted antiferromagnet at TN = 29 K with an estimated canting angle of 0.2−0.3°. Deduced from powder neutron diffraction data, the magnetic structure is modeled by alternate pairs of Ni(1) within a chain having their moments pointing along [010] and [01̄0], respectively. The moments of Ni(2) atoms are oppositely oriented with respect to their adjacent pairs. The resulting structure is that of a compensated arrangement of moments within one layer, comprising one ferromagnetic and three antiferromagnetic superexchange pathways between the nickel atoms.
