Layered oxyselenides Sr₂Co_1−xMn_xO₂Cu_2−δSe₂: The evolution of magnetic properties tuned by the competed interactions

Highlights: • 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. - Abstract: We have synthesized and investigated the magnetic properties of the layered oxyselenides Sr₂Co_1−xMn_xO₂Cu_2−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 (T_N) 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