We report a detailed study on the magnetic properties of the pyroxene series <i>M2</i><i>M1</i>Si<sub>2</sub>O<sub>6</sub>, with <i>M2</i> = Ca and <i>M1</i> = Mg, where magnesium and then calcium are progressively substituted by cobalt. For cobalt site occupancy larger than 0.7 at the <i>M1</i> site, a collinear antiferromagnetic phase is detected for T < T<sub>N1</sub> = 12 K with a monodimensional character (i.e. <i>M1</i> site intra-chain order parallel to <i>c</i> axis). Moreover the magnetization easy axis has been estimated to lie roughly along the  direction. Cobalt content ≥ 0.5 at the <i>M2</i> site (overall content 1.5) determines the formation of a new independent antiferromagnetic order with higher Néel temperatures, involving only the <i>M2</i> site intra-chain interactions. The incoming <i>M2</i> 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 <i>M1</i> or <i>M2</i> chains. Furthermore, metamagnetic transitions are observed for both <i>M1</i> and <i>M2</i> site intra-chain orders at relatively low critical magnetic fields, around 2 T, suggesting that this series of pyroxenes can be used as model system for investigating the fundamental aspects of magnetism in the matter.
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