RESUMEN

We report a detailed study on the magnetic properties of the pyroxene series M2M1Si2O6, with M2 = Ca and M1 = Mg, where magnesium and then calcium are progressively substituted by cobalt. For cobalt site occupancy larger than 0.7 at the M1 site, a collinear antiferromagnetic phase is detected for T < T N1 = 12 K with a monodimensional character (i.e. M1 site intra-chain order parallel to c axis). Moreover the magnetization easy axis has been estimated to lie roughly along the [1 0 1] direction. Cobalt content ⩾0.5 at the M2 site (overall content 1.5) determines the formation of a new independent antiferromagnetic order with higher Néel temperature, involving only the M2 site intra-chain interactions. The incoming M2 site order is accompanied by a lowering of the space symmetry which yields to a weakly ferromagnetic resultant due to spin canted distribution of the magnetic moments either along the M1 or M2 chains. Furthermore, metamagnetic transitions are observed for both M1 and M2 site intra-chain orders at relatively low critical magnetic fields, around 2 T, suggesting that this series of pyroxenes can be used as a model system for investigating the fundamental aspects of magnetism in the matter.