Structural and magnetic phase diagram and room temperature CMR effect of La1−xAgxMnO3

The study of the structural and magnetic phase diagram of the manganites La1−xAgxMnO3 shows similarity with the La1−x′Srx′MnO3 series, involving a metallic ferromagnetic domain at relatively high temperature (≈300 K). The Ag-system differs from the Sr-one by a much smaller homogeneity range (x≤1/6) and the absence of charge ordering. But the most important feature of the Ag-manganites deals with the exceptionally high magnetoresistance (−25%) at room temperature under 1.2 T, that appears for the composition x=1/6. The latter is interpreted as the coincidence of the optimal double exchange condition (Mn3+:Mn4+=2) with Tmax=300 K (maximum of the ρ(T) curve in zero field).