Electronic structure, magnetoresistance and spin filtering in graphene|2 monolayer-CrI33|graphene van der Waals magnetic tunnel junctions

Spin-Selective Memtransistors with Magnetized Graphene

Spin-polarized bands in pristine and proximity-induced magnetic materials are promising building blocks for future devices. Conceptually new memory, logic, and neuromorphic devices are conceived based on atomically thin magnetic materials and the manipulation of their spin-polarized bands via electrical and optical methods. A critical remaining issue is the direct probe and the optimized use of the magnetic coupling effect in van der Waals heterostructures, which requires further delicate design of atomically thin magnetic materials and devices. Here, a spin-selective memtransistor with magnetized single-layered graphene on a reactive antiferromagnetic material, CrI3, is reported. The spin-dependent hybridization between graphene and CrI3 atomic layers enables the spin-selective bandgap opening in the single-layered graphene and the electric field control of magnetization in a specific CrI3 layer. The microscopic working principle is clarified by the first-principles calculations and theoretical analysis of the transport data. Reliable memtransistor operations (i.e., memory and logic device-combined operations), as well as a spin-selective probe of Landau levels in the magnetized graphene, are achieved by using the subtle manipulation of the magnetic proximity effect via electrical means.

Non-uniform superlattice magnetic tunnel junctions

We propose a new class of non-uniform superlattice magnetic tunnel junctions (Nu-SLTJs) with the linear, Gaussian, Lorentzian, and Pöschl-Teller width and height based profiles manifesting a sizable enhancement in the TMR (≈10⁴- 10⁶%) with a significant suppression in the switching bias (≈9 folds) owing to the physics of broad-band spin filtering. By exploring the negative differential resistance region in the current-voltage characteristics of the various Nu-SLTJs, we predict the Nu-SLTJs offer fastest spin transfer torque switching in the order of a few hundred picoseconds. We self-consistently employ the atomistic non-equilibrium Green's function formalism coupled with the Landau-Lifshitz-Gilbert-Slonczewski equation to evaluate the device performance of the various Nu-SLTJs. We also present the design of minimal three-barrier Nu-SLTJs having significant TMR (≈10⁴%) and large spin current for the ease of device fabrication. We hope that the class of Nu-SLTJs proposed in this work may lay the bedrock to embark on the exhilarating voyage of exploring various non-uniform superlattices for the next generation of spintronic devices.

Large tunneling magnetoresistance in van der Waals magnetic tunnel junctions based on FeCl2 films with interlayer antiferromagnetic couplings

Antiferromagnets (AFMs) are some of the most promising candidates for next-generation magnetic memory technology owing to their advantages over conventional ferromagnets (FMs), such as zero stray field and THz-range magnetic resonance frequency. Motivated by the recent synthesis of FeCl₂ films with interlayer AFM and intralayer FM couplings, we investigated the magnetic properties of few-layer FeCl₂ and the spin-dependent transmissions of graphite/bilayer FeCl₂/graphite and Au/n-layer FeCl₂/Au magnetic tunnel junctions (MTJs) using first-principles calculations combined with the nonequilibrium Green's function. The interlayer AFM coupling of FeCl₂ is certified to be stable and independent of the stacking orders and relative displacement between layers. Furthermore, based on the Au electrode with better conductive performance than the graphite electrode and monolayer 1T-FeCl₂ with complete spin polarization, high Curie temperature and large magnetic anisotropic energy, a high tunnel magnetoresistance (TMR) ratio of 2.7 × 10³% is achieved in Au/bilayer FeCl₂/Au MTJs at zero bias and it increases with different layers of FeCl₂ (n = 2-10). These excellent spin transport properties of Au/n-layer FeCl₂/Au MTJs based on two-dimensional (2D) AFM barriers with out-of-plane magnetization directions suggest their great potential for application in high-reliability, high-speed and high-density spintronic devices.