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Register a new userCircuit-Model Analysis for Spintronic Devices with Chiral Molecules as Spin Injectors
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Recent research discovered that charge transfer processes in chiral molecules can be spin selective and named the effect chiral-induced spin selectivity (CISS). Follow-up work studied hybrid spintronic devices with conventional electronic materials and chiral (bio)molecules. However, a theoretical foundation for the CISS effect is still in development and the spintronic signals were not evaluated quantitatively. We present a circuit-model approach that can provide quantitative evaluations. Our analysis assumes the scheme of a recent experiment that used photosystem~I (PSI) as spin injectors, for which we find that the experimentally observed signals are, under any reasonable assumptions on relevant PSI time scales, too high to be fully due to the CISS effect. We also show that the CISS effect can in principle be detected using the same type of solid-state device, and by replacing silver with graphene, the signals due to spin generation can be enlarged four orders of magnitude. Our approach thus provides a generic framework for analyzing this type of experiments and advancing the understanding of the CISS effect.
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Here we emphasize once more the distinction between generating CISS (spin-charge current conversion) in a chiral system and detecting it as magnetoresistance in two-terminal electronic devices. We also highlight important differences between electrical measurement results obtained in the linear response regime and those obtained in the nonlinear regime.
In recent years, the field of antiferromagnetic spintronics has been substantially advanced. Electric-field control is a promising approach to achieving ultra-low power spintronic devices via suppressing Joule heating. In this article, cutting-edge research, including electric-field modulation of antiferromagnetic spintronic devices using strain, ionic liquids, dielectric materials, and electrochemical ionic migration, are comprehensively reviewed. Various emergent topics such as the Neel spin-orbit torque, chiral spintronics, topological antiferromagnetic spintronics, anisotropic magnetoresistance, memory devices, two-dimensional magnetism, and magneto-ionic modulation with respect to antiferromagnets are examined. In conclusion, we envision the possibility of realizing high-quality room-temperature antiferromagnetic tunnel junctions, antiferromagnetic spin logic devices, and artificial antiferromagnetic neurons. It is expected that this work provides an appropriate and forward-looking perspective that will promote the rapid development of this field.
Motivated by recent progress in development of cryogenic memory compatible with single flux quantum (SFQ) circuits we have performed a theoretical study of magnetic SIsFS Josephson junctions, where S is a bulk superconductor, s is a thin superconducting film, F is a metallic ferromagnet and I is an insulator. We calculate the Josephson current as a function of s and F layers thickness, temperature and exchange energy of F film. We outline several modes of operation of these junctions and demonstrate their unique ability to have large product of a critical current $I_{C}$ and a normal-state resistance $R_{N}$ in the $pi$ state, comparable to that in SIS tunnel junctions commonly used in SFQ circuits. We develop a model describing switching of the Josephson critical current in these devices by external magnetic field. The results are in good agreement with the experimental data for Nb-Al/AlO${_x}$-Nb-Pd$_{0.99}$Fe$_{0.01}$-Nb junctions.
We present a physics-based compact model for two-dimensional (2D) field-effect transistors (FETs) based on monolayer semiconductors such as MoS2. A semi-classical transport approach is appropriate for the 2D channel, enabling simplified analytical expressions for the drain current. In addition to intrinsic FET behavior, the model includes contact resistance, traps and impurities, quantum capacitance, fringing fields, high-field velocity saturation and self-heating, the latter being found to play a strong role. The model is calibrated with state-of-the-art experimental data for n- and p-type 2D-FETs, and it can be used to analyze device properties for sub-100 nm gate lengths. Using the experimental fit, we demonstrate feasibility of circuit simulations using properly scaled devices. The complete model is implemented in SPICE-compatible Verilog-A, and a downloadable version is freely available on the nanoHUB.org.
Topologically distinct magnetic structures like skyrmions, domain walls, and the uniformly magnetized state have multiple applications in logic devices, sensors, and as bits of information. One of the most promising concepts for applying these bits is the racetrack architecture controlled by electric currents or magnetic driving fields. In state-of-the-art racetracks, these fields or currents are applied to the whole circuit. Here, we employ micromagnetic and atomistic simulations to establish a concept for racetrack memories free of global driving forces. Surprisingly, we realize that mixed sequences of topologically distinct objects can be created and propagated over far distances exclusively by local rotation of magnetization at the sample boundaries. We reveal the dependence between the chirality of the rotation and the direction of propagation and define the phase space where the proposed procedure can be realized. The advantages of this approach are the exclusion of high current and field densities as well as its compatibility with an energy-efficient three-dimensional design.
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