Magnetic diamond chains of $Cu_3O_4$

We present magnetization measurements on a satellite phase of $YBa_2Cu_3O_x$ namely $BaCu_3O_4$. This two-dimensional material is composed of alternate layers of Ba and $Cu_3O_4$. In the latters, the Cu and O atoms are one-dimensionaly ordered in diamond-shaped chains of formula unit $Cu_3O_4$. We will show that this material encounters a magnetic phase transition at around 336 K which is due to intra-ordering through superexchange coupling of the spins born by the Cu atoms in these diamond chains. We will discuss the possibility of either ferrimagnetic or antiferromagnetic inter-ordering of these weakly coupled one-dimensional objects and the possible role of Dzyaloshinskii-Moriya interactions.