Increasing the Magnetic Order Temperature in Co 3 O 2 BO 3 :In Ludwigite.

Below 42 K, the homometallic Co 3 O 2 BO 3 ludwigite forms magnetic planes separated by nonmagnetic low-spin Co 3+ ions. The substitution of Co 3+ by other nonmagnetic ions enhances the magnetic interactions, raising the magnetic ordering temperature. However, depending on the nonmagnetic dopant ion, the remaining Co 3+ ions could adopt a high-spin state, creating magnetic frustration and lowering the magnetic transition temperature. Doping Co 3 O 2 BO 3 with nonmagnetic In 3+ ions favors the appearance of both high-spin Co 2+ and Co 3+ . The In 3+ ions preferentially occupy sites 4 and are randomly distributed in each site. The two-dimensional magnetic character of the parent compound, Co 3 O 2 BO 3 , 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 Co 3 O 2 BO 3 with different nonmagnetic +3 ions are discussed in terms of the presence of high-spin Co 2+ and Co 3+ in the compounds.