Nonmagnetic ions enhance magnetic order in the ludwigite Co5Sn(O2BO3)2

The ludwigite Co5Sn(O2BO3)(2) was studied using x-ray diffraction, Mossbauer spectroscopy, andmagnetic and thermodynamic measurements. This material belongs to a family of oxyborates which presents low-dimensional subunits in the form of three-leg ladders in its structure. The subunits confer to these materials a strong anisotropy in their exchange interactions that provide to the ludwigites several interesting magnetic properties, from partial ordering to spin-glass states. Despite being doped by nonmagnetic ions, Co5Sn(O2BO3)(2) has long-range magnetic order below 82 K which is, surprisingly, the highest critical temperature found so far in the ludwigites. This record can be explained by the absence of double-exchange interactions, usually present in the ludwigites and that gives rise to strong competition. In this paper we study the magnetic and structural properties of Co5Sn(O2BO3)(2) and compare our results with those obtained in other cobalt ludwigites.