Synthesis and Characterization of the Electron-Doped Single-Layer Manganite La1.2Sr0.8MnO4- and Its Oxidized Phase La1.2Sr0.8MnO4+

The electron-doped single-layer manganite, La1.2Sr0.8MnO3.94, has been synthesized under reducing conditions. It has the K2NiF4 type structure (space group I4/mmm) with a unit cell of a=3.82698(2) ? and c=13.06858(7) ?. Magnetic susceptibility study of the as-synthesized sample shows a broad maximum at 110 K, which is attributed to an antiferromagnetic transition. When the sample is treated at 550°C in air, interstitial oxygen is incorporated, resulting in an oxidized phase of composition La1.2Sr0.8MnO4.27. The oxidation results in expansion in the ab plane (a=3.93477(5) ?) and a large contraction along the c axis (c=12.5237(2) ?). Although ferromagnetic Mn–Mn interactions are indicated at high temperatures for La1.2Sr0.8MnO4.27, they do not lead to any long–range magnetic order at low temperature. Instead, spin glass behavior is observed with a freezing temperature of Tf=19.5 K.