Layered oxyselenides Sr2Co1−xMnxO2Cu2−δSe2: The evolution of magnetic properties tuned by the competed interactions

• The copper-deficiency increases when Co is substituted by Mn.
• The doping of Mn introduces the FM interaction in the Co/MnO2 planes.
• The competition of AFM and FM results in the appearance of the SG state.
• The coexistence of AFM order and SG state is observed.

We have synthesized and investigated the magnetic properties of the layered oxyselenides Sr2Co1−xMnxO2Cu2−δSe2 (0 ⩽ x ⩽ 1). They crystallize in an unusual intergrowth structure with Cu2Se2 and (Co,Mn)O2 layers separated by Sr ions. The refinement of the X-ray diffraction data reveals an increase in the copper-deficiency when Co is substituted by Mn, which is caused by oxidization of Mn2+ ions. The antiferromagnetic (AFM) transition temperature (TN) shifts to lower temperature and the dominant in plane interaction changes from AFM to ferromagnetic (FM) with Mn doping. The coexistence of AFM order and SG state is observed for compositions with 0.25 ⩽ x ⩽ 0.5.