Anomalous room temperature magnetoresistance in brownmillerite Ca<inf>2</inf>Fe<inf>2</inf>O<inf>5</inf>

We demonstrate the hitherto unreported field induced magnetoresistance in wet chemical synthesized bulk polycrystalline brownmillerite Ca2Fe2O5. A magnetoresistance of 12% is observed at room temperature, well below its antiferromagnetic transition temperature of 775 K. The variation in resistivity with increasing and decreasing magnetic field shows a significant memory effect. When synthesized in a nanostructured form it exhibits weak ferromagnetism due to the appearance of an Fe oxide phase, besides exhibiting a shift to a higher antiferromagnetic Néel temperature of 820 K. Spectroscopic investigations (X-ray photoelectron and Raman spectroscopy) as well as magnetic measurements have been employed to investigate the above behavior of brownmillerite Ca2Fe2O5.