Unidirectional spin Hall magnetoresistance in topological\n insulator/ferromagnetic layer heterostructures

Abstract

The large spin orbit coupling in topological insulators results in helical\nspin-textured Dirac surface states that are attractive for topological\nspintronics. These states generate an efficient spin-orbit torque on proximal\nmagnetic moments at room temperature. However, memory or logic spin devices\nbased upon such switching require a non-optimal three terminal geometry, with\ntwo terminals for the writing current and one for reading the state of the\ndevice. An alternative two terminal device geometry is now possible by\nexploiting the recent discovery of a unidirectional spin Hall magnetoresistance\nin heavy metal/ferromagnet bilayers and (at low temperature) in magnetically\ndoped topological insulator heterostructures. We report the observation of\nunidirectional spin Hall magnetoresistance in a technologically relevant device\ngeometry that combines a topological insulator with a conventional\nferromagnetic metal. Our devices show a figure-of-merit (magnetoresistance per\ncurrent density per total resistance) that is comparable to the highest\nreported values in all-metal Ta/Co bilayers.\n