Hydrothermal Synthesis in the System Ni(OH)₂−NiSO₄: Nuclear and\nMagnetic Structures and Magnetic Properties of Ni₃(OH)₂(SO₄)₂(H₂O)₂

Abstract

We present the synthesis, characterization by DT-TGA and IR, single crystal X-ray nuclear structure at 300 K,\nnuclear and magnetic structure from neutron powder diffraction on a deuterated sample at 1.4 K, and magnetic\nproperties as a function of temperature and magnetic field of Ni₃(OH)₂(SO₄)₂(H₂O)₂. The structure is formed of\nchains, parallel to the <i>c</i>-axis, of edge-sharing Ni(1)O₆ octahedra, connected by the corners of Ni(2)O₆ octahedra\nto form corrugated sheets along the <i>bc</i>-plane. The sheets are connected to one another by the sulfate groups to\nform the 3D network. The magnetic properties measured by ac and dc magnetization, isothermal magnetization at\n2 K, and heat capacity are characterized by a transition from a paramagnet (<i>C</i> = 3.954 emu K/mol and θ = −31\nK) to a canted antiferromagnet at <i>T</i>_N = 29 K with an estimated canting angle of 0.2−0.3°. Deduced from powder\nneutron diffraction data, the magnetic structure is modeled by alternate pairs of Ni(1) within a chain having their\nmoments pointing along [010] and [01̄0], respectively. The moments of Ni(2) atoms are oppositely oriented with\nrespect to their adjacent pairs. The resulting structure is that of a compensated arrangement of moments within\none layer, comprising one ferromagnetic and three antiferromagnetic superexchange pathways between the nickel\natoms.