| Abstract
| - We report the synthesis, crystal structure derived from X-ray single crystal and neutron powder dataat 300 K, infrared spectra, thermogravimetric analysis, and the magnetic properties of Co3(OH)2(SO4)2(H2O)2 and its deuterated (d6-) analogue, as well as the magnetic structure from neutron powder data ofthe latter as a function of temperature. The structure consists of corrugated metal-hydroxide layers withintralayer μ6-sulfate, and the layers are connected to one another by μ4-sulfate. The magnetic propertiesexhibit a transition from a paramagnet to a canted-antiferromagnet at 42 K and display an unusual hystereticspontaneous magnetization with temperature. The paramagnetic region is characterized by Curie constantsof ∼9.5 emu K/mol and a Weiss constant of ∼ −70 K. From the remanant magnetization, extrapolatedfrom the linear dependence of the isothermal magnetization with field, we estimate the canting angle tobe <0.2°. Refinement of the magnetic structure from data collected on two different diffractomers (D20at ILL, Grenoble, and G4.1 at CEA, Saclay) and considering the group analysis of Bertaut's, we find themoments to lie along the c-axis with complete compensation of the moments within one layer. Thetemperature dependence of the moments of the two cobalt atoms also reflects the hysteresis observed inmagnetization. The magnetic model is in good agreement with magnetization measurements performedon an aligned single crystal along the three orthogonal axes of the orthorhombic unit cell.
- The layered cobalt hydroxysulfate, Co3(OH)2(SO4)2(H2O)2, contains μ3-OH, μ2-OH2, μ4-SO4, and μ6-SO4, providing magnetic exchange pathways between cobalt atoms which result in an antiferromagnetic ground state below 42 K with a small spontaneous magnetization, possibly due to hidden canting. It exhibits textbook temperature-dependent ac- and dc- magnetic susceptibilities along its three orthogonal axes of the orthorhombic unit cell defining the easy axis along c (red circles), the hard and also canting axis along b (blue circles), and the intermediate axis along a (green circles), in good agreement with the magnetic structure (inset) derived from neutron powder data.
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