Nuclear and Magnetic Structures and Magnetic Properties of Co3(OH)2(SO4)2(H2O)2. Comparison to the Mn and Ni Analogues

Abstract

We report the synthesis, crystal structure derived from X-ray single crystal and neutron powder data at 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 of the latter as a function of temperature. The structure consists of corrugated metal-hydroxide layers with intralayer μ6-sulfate, and the layers are connected to one another by μ4-sulfate. The magnetic properties exhibit a transition from a paramagnet to a canted-antiferromagnet at 42 K and display an unusual hysteretic spontaneous magnetization with temperature. The paramagnetic region is characterized by Curie constants of ∼9.5 emu K/mol and a Weiss constant of ∼ −70 K. From the remanant magnetization, extrapolated from the linear dependence of the isothermal magnetization with field, we estimate the canting angle to be <0.2°. Refinement of the magnetic structure from data collected on two different diffractomers (D20 at ILL, Grenoble, and G4.1 at CEA, Saclay) and considering the group analysis of Bertaut's, we find the moments to lie along the c-axis with complete compensation of the moments within one layer. The temperature dependence of the moments of the two cobalt atoms also reflects the hysteresis observed in magnetization. The magnetic model is in good agreement with magnetization measurements performed on an aligned single crystal along the three orthogonal axes of the orthorhombic unit cell.