Magnetic tunnel junctions with MgO-EuO composite tunnel barriers

Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. The chalcogenide compound EuO is best known as a highly efficient spin-filter tunnel barrier material. Using the molecular beam epitaxy method, we combine polycrystalline EuO with epitaxial MgO and construct magnetic tunnel junctions with such hybrid tunnel barriers. Tunnel magnetoresistance of over 40% was achieved in junctions with oxygen-rich EuO. For lower oxygen concentration, magnetoresistance decreases dramatically and eventually vanishes, indicating that spin filtering is weakened when the transport is mainly mediated by excess conduction channels through defect sites.