Insights into the Co/MoS₂/Co magnetic tunnel junctions

Magnetic tunnel junctions (MTJ) composed of two-dimensional (2D) van der Waals heterostructures are proposed to be a plausible scheme to achieve larger tunnel magnetoresistance (TMR) than the conventional MTJs. The spin transport across the interfaces is affected not only by the Brillouin zone (BZ) filtering but also by the interfacial bonds. This work focuses on studying the 2H Molybdenum Disulfide (MoS₂) van der Waals layers as the tunnel barrier, and Cobalt (Co) as the electrode. The TMR varies with different adsorption interfaces, yet none have achieved the desired levels because the momentum-resolved transmissions of Co and MoS₂ in the folded horizontal BZ do not match well, resulting in inefficient spin filtering and thereby a low TMR. The effects of interfacial bonds on spin transport and magnetic anisotropy are studied. The orientations of bonds determine the anisotropy of the interfacial Co. Vertical bonds stabilize the perpendicular magnetic anisotropy (PMA), while non-vertical bonds cause in-plane magnetic anisotropy (IMA). The layers below exhibit PMA, so both types of MTJs overall support PMA, while the physisorbed MTJ is stronger. The positive relation between the transmission and the electron density near the Fermi level is weakened by the bonds, as the scattering centers hold back the spin injection. Our work further strengthens the importance of BZ filtering in governing TMR and the design principle of MTJ, as well as how bonds affect the overall device performance.