In recent years antiferromagnets (AFMs) have become very promising for nanoscale spintronic applications due to their unique properties such as THz dynamics and absence of stray fields. Manipulating antiferromagnetic textures is currently, however, limited to very few exceptional material symmetry classes allowing for staggered torques on the magnetic sublattices. In this work, we predict for kagome AFMs with broken mirror symmetry a new coupling mechanism between antiferromagnetic domain walls (DWs) and spin currents, produced by the relativistic Dzyaloshinskii-Moriya interaction (DMI). We microscopically derive the DMI's free energy contribution for the kagome AFMs. Unlike ferromagnets and collinear AFMs, the DMI does not lead to terms linear in the spatial derivatives but instead renormalizes the spin-wave stiffness and anisotropy energies. Importantly, we show that the DMI induces a highly nontrivial twisted DW profile that is controllable via two linearly independent components of the spin accumulation. This texture manipulation mechanism goes beyond the concept of staggered torques and implies a higher degree of tunability for the current-driven DW motion compared to conventional ferromagnets and collinear AFMs.

The long fascination that antiferromagnetic materials has exerted on the scientific community over about a century has been entirely renewed recently with the discovery of several unexpected phenomena, including various classes of anomalous spin and charge Hall effects and unconventional magnonic transport, and also homochiral magnetic entities such as skyrmions. With these breakthroughs, antiferromagnets stand out as a rich playground for the investigation of novel topological behavior, and as promising candidate materials for disruptive low-power microelectronic applications. Remarkably, the newly discovered phenomena are all related to the topology of the magnetic, electronic or magnonic ground state of the antiferromagnets. This review exposes how non-trivial topology emerges at different levels in antiferromagnets and explores the novel mechanisms that have been discovered recently. We also discuss how novel classes of quantum magnets could enrich the currently expanding field of antiferromagnetic spintronics and how spin transport can in turn favor a better understanding of exotic quantum excitations.

The ac spin pumping of noncollinear antiferromagnets is theoretically investigated. Starting from an effective action description of the spin system, we derive the Onsager coefficients connecting the spin pumping and spin-transfer torque associated with the dynamics of the SO(3)-valued antiferromagnetic order parameter. Our theory is applied to a kagome antiferromagnet resonantly driven by a uniform external magnetic field. We demonstrate that the reactive (dissipative) spin-transfer torque parameter can be extracted from the pumped ac spin current in-phase (in quadrature) with the driving field. Furthermore, we find that the three spin-wave bands of the kagome AF generate spin currents with mutually orthogonal polarization directions. This offers a unique way of controlling the spin orientation of the pumped spin current by exciting different spin-wave modes.

We predict a mechanism to controllably manipulate domain walls in kagome antiferromagnets via a single linearly polarized spin-wave source. We show by means of atomistic spin dynamics simulations of antiferromagnets with kagome structure that the speed and direction of the domain wall motion can be regulated by only tuning the frequency of the applied spin wave. Starting from microscopics, we establish an effective action and derive the corresponding equations of motion for the spin-wave-driven domain wall. Our analytical calculations reveal that the coupling of two spin-wave modes inside the domain wall explains the frequency-dependent velocity of the spin texture. Such a highly tunable spin-wave-induced domain wall motion provides a key component toward next-generation fast, energy-efficient, and Joule-heating-free antiferromagnetic insulator devices.

While antiferromagnetic skyrmions display appealing properties, their lateral expansion in the high-velocity regime hinders their potential for applications. In this work, we study the impact of spin Hall torque, spin transfer torque, and topological torque on the velocity-current relation of antiferromagnetic skyrmions with the aim of reducing this deformation. Using a combination of micromagnetic simulations and analytical derivations, we demonstrate that the lateral expansion of the antiferromagnetic skyrmion is reminiscent of the well-known Lorentz contraction identified in one-dimensional antiferromagnetic domain walls. We also show that in the flow regime the lateral expansion is accompanied by a progressive saturation of the skyrmion velocity when driven by spin Hall and topological torques. This saturation occurs at much smaller velocities when driven by the topological torque, while the lateral expansion is reduced, preventing the skyrmion size from diverging at large current densities. We extend this study toward synthetic antiferromagnets, where the weaker antiferromagnetic exchange leads to much larger lateral expansion at smaller current densities in all cases. This study suggests that a compromise must be made between skyrmion velocity and lateral expansion during the device design. In this respect, exploiting the topological torque could lead to better control of the skyrmion velocity in antiferromagnetic racetracks.

We consider current-driven motion of magnetic skyrmions in granular magnetic films. The study uses micromagnetic modeling and phenomenological analysis based on the Thiele formalism. Remarkably, disorder enhances the effective skyrmion Hall effect that depends on the magnitude of the driving force (current density and non-adiabaticity parameter). The origin is sliding motion of the skyrmion along the grain boundaries, followed by pinning and depinning at the grain junctions. A side-jump can occur during this depinning process. In addition, the critical current that triggers the skyrmion motion depends on the relative size of the crystallites with respect to the skyrmion size. Finally, when the skyrmion trajectory is confined along an edge by the non-adiabatic Magnus force, the critical current density can be significantly reduced. Our results imply that narrow nanowires have higher skyrmion mobilities.

A next-generation memory device utilizing a three-dimensional nanowire system requires the reliable control of domain wall motion. In this letter, domain walls are studied in cylindrical nanowires consisting of alternating segments of cobalt and nickel. The material interfaces acting as domain wall pinning sites, are utilized in combination with current pulses, to control the position of the domain wall, which is monitored using magnetoresistance measurements. Magnetic force microscopy results further confirm the occurrence of current assisted domain wall depinning. Data bits are therefore shifted along the nanowire by sequentially pinning and depinning a domain wall between successive interfaces, a requirement necessary for race-track type memory devices. We demonstrate that the direction, amplitude and duration of the applied current pulses determine the propagation of the domain wall across pinning sites. These results demonstrate a multi-bit cylindrical nanowire device, utilizing current assisted data manipulation. The prospect of sequential pinning and depinning in these nanowires allows the bit density to increase by several Tbs, depending on the number of segments within these nanowires.

This paper investigates the influence of electron–electron scattering on spin relaxation length in bilayer graphene using semiclassical Monte Carlo simulation. Both D’yakonov–P’erel and Elliot–Yafet mechanisms are considered for spin relaxation. It is shown that spin relaxation length decreases by 17 % at 300 K on including electron–electron scattering. The reason of this variation in spin relaxation length is that the ensemble spin is modified upon an e–e collision, and also e–e scattering rate is greater than phonon scattering rate which causes change in spin transport profile.

In this paper we combine out-of-plane spin value Magnetic Tunnel Junctions (MTJ) with a Voltage controlled magnetic anisotropy (VCMA) MTJ in order to reduce the switching time of MTJs. We find that the switching time can be decreased significantly by combining an out-of-plane spin value MTJ with a VCMA MTJ. With a Conventional Spin Value (CSV) MTJ we achieve a switching time of 5 ns but after combining both the effects, out-of-plane polarisation (OPPP) and VCMA, we are able to decrease the switching time to upto 0.022 ns which is approximately 227.27 times less than the CSV device.

In this paper, we study the effects of non-uniform channel doping on junctionless transistor (JLT) using 3D quantum simulations. The JLT devices require a uniformly doped ultrathin channel. Although we take uniform doping for study, in practice, it will be technologically difficult to obtain. For technological reason, after thermal annealing, the impurity profile in semiconductor device becomes uniform along lateral channel direction and non-uniform along vertical direction. Here, we show that this directly affects the short channel behaviour and reduces on-current.

This paper presents the design of 2-bit Binary Divider using Quantum Dots (QDs) in Single Spin Logic (SSL) paradigm where single electron hosted in QDs act as binary logic device in which spin orientation of electrons encodes the bit information in presence of weak magnetic field. Information is transmitted from one spin to next via nearest-neighbor exchange interaction. Major advantages of SSL is lesser power dissipation, improved speed and dense structures.

Analysis of thermal and electrical characteristics of the proposed device, selective buried oxide junctionless transistor (SELBOX-JLT) along with its analog performance, is compared with silicon on insulator junctionless transistor (SOI-JLT). The proposed device shows better thermal efficiency. The maximum device temperature of SELBOX-JLT is 311 K, much less than that of SOI-JLT (445 K). The proposed device has almost no effect of self-heating on output characteristics. SELBOX-JLT exhibits better I ON / I OFF ratio, subthreshold slope, and drain-induced barrier lowering as compared to SOI-JLT for the same channel length. The analog performance parameters as transconductance ( G m ), transconductance/drain current ratio ( G m / I D ), drain conductance ( G D ), output resistance ( R 0 ), intrinsic gain ( G m R 0 ), and unity-gain frequency ( f T ) of the proposed device are found to be better than SOI-JLT.

In this paper, we try to access all possible memory combinations in a memristor crossbar array, reduce the effect of sneak path currents and also make read faster and simpler. For this, we analyze a balanced pattern architecture using a memristive crossbar array and also propose an effective read technique. We aim at reducing the problem of variability in the sneak path currents. Also from the read technique proposed, we reduce the measurements to read memory from the array.

Semiclassical Monte Carlo simulation is used to determine the effect of microscopic ripples on spin relaxation length in freely suspended single-layer graphene. Spin relaxation lengths are simulated using D’yakonov–Perel mechanisms, with comparisons made by including ripple scattering mechanisms along with phonon scattering. The results are simulated with varying temperatures and concentration.

In this paper we discuss an idea of levels, which is a hierarchical nested local search based on solutions of existing global optimization approach. We implement the idea by designing an algorithm that treats random sampling, ant colony optimization algorithms for continuous domain and quantum ant colony optimization as its parent algorithms. We compare and study the results of the newly designed algorithms with their respective parent algorithms for similar test setups on certain benchmark test functions.