Spin filtering effect, thermal spin diode effect and high tunneling magnetoresistance in the Au/GdI/Au van der Waals junction.

2D van der Waals magnets have been widely studied in spintronics because of their unique electronic properties, no dangling bonds, and ultra-clean interfaces. However, most of them possess low Curie temperatures. Motivated by the recent discovery of a near-room-temperature ferromagnetic semiconductor in monolayer GdI, we proposed the Au/GdI/Au vertical van der Waals junction and investigated the bias-voltage- and temperature-gradient-dependent spin transport characteristics using density functional theory and the non-equilibrium Green's function method. It is found that, like bulk GdI, the four-layer GdI in the central scattering region of the junction exhibits intralayer ferromagnetism with weak interlayer antiferromagnetic coupling. An almost 100% spin polarization can be obtained whether at a bias voltage or at a temperature gradient for the junction, while high tunneling magnetoresistances are observed in a large bias voltage range or in a large temperature gradient range, which can reach 29000% and 3600%, respectively. The junction also exhibits a thermal spin diode effect. These versatile bias voltage- and temperature gradient-driven spin transport properties are understood from the calculated spin-dependent band structure of layered GdI and the spin-dependent transmission spectrum and density of states of the junction. The present work highlights layered GdI as a promising magnetic tunnel barrier for van der Waals spintronic devices and spin caloritronic devices.