Crystal and magnetic structures of new layered oxides A2GaMnO5+y (A=Ca, Sr)
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Crystal and magnetic structures of new complex manganese oxides A2GaMnO5+y (A=Ca,Sr) were studied by neutron diffraction. Being perovskite-type derivatives, their crystal structures belong to a brownmillerite type and consist of alternating (CaO), (MnO2), (CaO) and (GaO) or (GaO1+x) layers. At temperatures between ≈(100-200) K, these compounds undergo transitions into antiferromagnetic states. The magnetic ordering type depends on the compositions. The Mn magnetic moments are aligned in opposite directions within the MnO2 layer, and the coupling between magnetic moments lying in the adjacent MnO2 layers is, for example, antiferromagnetic for the reduced, and ferromagnetic for the oxidized Sr-containing compound Sr2GaMnO5 and Sr2GaMnO5.52 compositions, respectively.