Abstract
Neutron diffraction investigations of orthorhombic Co3 11B7O13Br at 293 K and in the temperature range 1.5–30 K reveal a two step onset of magnetic ordering, starting at the the second order transition to a weakly ferromagnetic phase at T N = 17.5 K (Néel type) and followed at about T t = 10.5 K, by a smooth transformation to a three-dimensional canted magnetic structure (magnetic space group Pc′a21′ (Sh29 101), magnetic modes C x(+ + − −), F y(+ + + +), A z(+ − − +). The three Co sites display completely different moment values and directions, arising from frustration effects associated with the formation of isolated Co3Br groups with a triangular arrangement of the three Co sites.