Unidirectional spin Hall magnetoresistance in topological insulator/ferromagnetic layer heterostructures

摘要

The large spin orbit coupling in topological insulators results in helicalspin-textured Dirac surface states that are attractive for topologicalspintronics. These states generate an efficient spin-orbit torque on proximalmagnetic moments at room temperature. However, memory or logic spin devicesbased upon such switching require a non-optimal three terminal geometry, withtwo terminals for the writing current and one for reading the state of thedevice. An alternative two terminal device geometry is now possible byexploiting the recent discovery of a unidirectional spin Hall magnetoresistancein heavy metal/ferromagnet bilayers and (at low temperature) in magneticallydoped topological insulator heterostructures. We report the observation ofunidirectional spin Hall magnetoresistance in a technologically relevant devicegeometry that combines a topological insulator with a conventionalferromagnetic metal. Our devices show a figure-of-merit (magnetoresistance percurrent density per total resistance) that is comparable to the highestreported values in all-metal Ta/Co bilayers.