Nanomagnetism variation with fluorine content in Co(OH)F

Magnetic behaviors of cobalt hydroxide fluoride, Co(OH)F_2-x F_x (x = 1.09 and 1.26), which are consisted with nanorods of ∼5 μm length and diameter ∼100 nm, obtained by a facile hydrothermal method, have been researched with the variation of fluorine content as a result of the different amount of reactant NH₄F addition. Magnetic coupling performance are characterized based on the observation and analysis of magnetic susceptibility, X-ray Absorption Fine Structure (XAFS) and specific heat. Co(OH)F_2-x is found to undergo an antiferromagnetic transition at 40 K. The peak temperature (T) on the transition curves shifts to lower temperature according with the increased magnetic field (H) following the rule of H^2/3∞ (-T) because of the surface spin-glass behavior. The paramagnetic susceptibility can be fitted with the modified Curie–Weiss law between 100 K and 320 K. The negative Curie-Weiss temperature indicates that the antiferromagnetic coupling becomes stronger with the fluorine content. In addition, at temperatures below 5 K, the magnetic reordering was observed as spin-glass. Exchange bias behavior in Co(OH)F_2-x was found after field cooling process demonstrating an exotic surface magnetic behavior generated with high fluorine contents due to the deformation of CoO₆ octahedral induced large spin-glass behavior.