Giant Seebeck magnetoresistance triggered by electric field and assisted by a valley through a ferromagnetic/antiferromagnetic junction in heavy group-IV monolayers

Electrons in heavy group-IV monolayers, including silicene, germanene, and stanene, have the ability to exhibit rich physics due to the compatibility of the spin and valley degrees of freedom. We propose here that a valley-mediated giant Seebeck magnetoresistance (MR) effect, triggered and controlled by an interlayer electric field E_z, can be engineered near room temperature in a ferromagnetic/antiferromagnetic (FM/AFM) junction based on heavy group-IV monolayers, where the FM and AFM fields can be induced by the proximity effect, and E_z is locally applied in the AFM region. Attributed to the specific tunneling mechanism of spin-valley matching, the high thermal MR state is dominated by a Seebeck state with nearly pure spin current (no charge current) from one valley under E_z=0 , while the low thermal MR state is dominated by a spin filter state from the other valley under E_z≠0 . We also demonstrate that such a giant Seebeck MR effect is robust against the small perturbation of the Fermi level, and is sensitive to E_z by changing the electron-hole transport symmetry and tuning the bands. Further calculations indicate that the Seebeck MR effect is relatively too weak in other magnetic junctions, typically the FM/E_z and AFM/E_z junctions, even when the pure-spin-current state is present. These findings may pave the way for heavy group-IV monolayers in developing valley-assisted thermomagnetic storing and reading technologies in future spin caloritronic devices.