Unidirectional spin-Hall and Rashba−Edelstein magnetoresistance in topological insulator-ferromagnet layer heterostructures

Abstract

The large spin−orbit coupling in topological insulators results in helical spin-textured Dirac surface states that are attractive for topological spintronics. These states generate an efficient spin−orbit torque on proximal magnetic moments. However, memory or logic spin devices based upon such switching require a non-optimal three-terminal geometry, with two terminals for the writing current and one for reading the state of the device. An alternative two-terminal device geometry is now possible by exploiting the recent discovery of the unidirectional spin Hall magnetoresistance in heavy metal/ferromagnet bilayers and unidirectional magnetoresistance in magnetic topological insulators. Here, we report the observation of such unidirectional magnetoresistance in a technologically relevant device geometry that combines a topological insulator with a conventional ferromagnetic metal. Our devices show a figure of merit (magnetoresistance per current density per total resistance) that is more than twice as large as the highest reported values in all-metal Ta/Co bilayers.

Chiral spin ordering of electron gas in solids with broken time reversal symmetry

“…Our study suggests that the emergence of chiral spin textures in an electron gas driven by an electrostatic disorder is a universal phenomenon, which is expected in a variety of experimentally studied systems, such as DMS 40,46 , thin films of ferromagnets 32,33 , Bi 2 Se 3 doped by magnetic impurities 30,31,47,48 , or due to the proximity effect 49 with magnetic insulators 50 , or ferromagnets 51,52 . The derived analytical expressions for the spin-density response functions can be used to qualitatively analyze the effect in these systems and to treat the interplay between the spin-orbit interaction and Zeeman spin splitting of carriers in particular.…”

Giant gate-controlled proximity magnetoresistance in semiconductor-based ferromagnetic–non-magnetic bilayers

“…In particular, the MPE at FM/NM interfaces where the NM layer is a material with strong spin-orbit coupling-typically a heavy metal, TI, or a two-dimensional electron gas (2DEG) with a strong Rashba effect-has attracted much attention as these materials represent promising components for spintronics devices and as a route toward realizing Majorana fermions 17,18 . Using such FM/NM interfaces, several groups have reported new proximity-originated MR effects [5][6][7][8][9][10] , which have led to a new ability to manipulate electron transport in the NM channel by the magnetization of the FM layer. However, the MR ratio is too small (0.01 ~ 1%) to consider any application, and the MR and related properties cannot be controlled by external means, such as a gate voltage, because of the short-range magnetic coupling (~1 nm) at these FM/NM interfaces and the short Thomas-Fermi screening length (~0.1 nm) in the metallic NM channels.…”

Phase Locking of a Pair of Ferromagnetic Nano-oscillators on a Topological Insulator

“…The typical value of the magnetization is on the order of 1000 Oe 75,76 . Another widely studied heterostructure Bi 2 Se 3 /EuS 71,77-79 , where progress on magnetoresistance and current-induced magnetization switching has been recently reported 79 . For EuS, the hard axis anisotropy is in the range 77,78 of 10 4 − 10 5 erg/cm 3 , and the value of magnetization 78 is also on the order of 1000 Oe.…”