Increasing the Magnetic Order Temperature in Co₃O₂BO₃:In Ludwigite

Below 42 K, the homometallic Co₃O₂BO₃ ludwigite forms magnetic planes separated by nonmagnetic low-spin Co³⁺ ions. The substitution of Co³⁺ by other nonmagnetic ions enhances the magnetic interactions, raising the magnetic ordering temperature. However, depending on the nonmagnetic dopant ion, the remaining Co³⁺ ions could adopt a high-spin state, creating magnetic frustration and lowering the magnetic transition temperature. Doping Co₃O₂BO₃ with nonmagnetic In³⁺ ions favors the appearance of both high-spin Co²⁺ and Co³⁺. The In³⁺ ions preferentially occupy sites 4 and are randomly distributed in each site. The two-dimensional magnetic character of the parent compound, Co₃O₂BO₃, is preserved, and the magnetic transition temperature increases to 47.8 K. Measurements of magnetization, which show metamagnetic transitions at low temperatures, and specific heat are consistent with ferrimagnetic ordering in this system. Thus, using these results and those reported in the literature, the effects caused by doping of Co₃O₂BO₃ with different nonmagnetic +3 ions are discussed in terms of the presence of high-spin Co²⁺ and Co³⁺ in the compounds.