Spintronics, utilizing both the charge and spin of electrons, benefits from the nonvolatility, low switching energy, and collective behavior of magnetization. These properties allow the development of magnetoresistive random access memories, with magnetic tunnel junctions (MTJs) playing a central role. Various spin logic concepts are also extensively explored. Among these, spin logic devices based on the motion of magnetic domain walls (DWs) enable the implementation of compact and energy-efficient logic circuits. In these devices, DW motion within a magnetic track enables spin information processing, while MTJs at the input and output serve as electrical writing and reading elements. DW logic holds promise for simplifying logic circuit complexity by performing multiple functions within a single device. Nevertheless, the demonstration of DW logic circuits with electrical writing and reading at the nanoscale is still needed to unveil their practical application potential. In this review, we discuss material advancements for high-speed DW motion, progress in DW logic devices, groundbreaking demonstrations of current-driven DW logic, and its potential for practical applications. Additionally, we discuss alternative approaches for current-free information propagation, along with challenges and prospects for the development of DW logic.

We present a novel method combining anodic aluminum oxide template synthesis and nanolithography to selectively deposit vertically patterned magnetic nanowires on a Si substrate. With this approach we fabricated three-dimensional nanowire-based spin valve devices without the need of complex etching processes or additional spacer coating. Through this method, we successfully obtained NiCu/Cu multilayered nanowire arrays with a controlled sequence along the long axis of the nanowires. Both magnetic switching and excitation phenomena driven by spin-polarized currents were clearly demonstrated in our NiCu/Cu multilayered nanowires. Moreover, the critical currents for switching and excitation were observed to be modulated in an oscillatory manner by the magnetic field in the nanowire-based devices. We present a toy model to qualitatively explain these observations.

This article performs computer simulations of the change in magnetization in the ferromagnetic film when polarized electric current passes through it. The model examines multilayer structures from ferromagnetic and nonmagnetic films. A sandwich system comprises two ferromagnetic layers separated by a nonmagnetic gasket. Ferromagnetic films have different magnetic susceptibility. The first ferromagnetic film is magnetically hard and acts as a fixed layer. The second ferromagnetic film is magnetically soft, with a switched direction of magnetization. The current direction is perpendicular to the film plane (CPP geometry). Spin transfer is carried out by electrons that polarize in the first ferromagnetic film and transmit spin to the second ferromagnetic film. We use the Ising model to describe the magnetic properties of the system and the Metropolis algorithm to form the thermodynamic states of the spin system. Simulations are performed at temperatures below the Curie points for both materials. The result of computer simulation is the dependence of magnetization in the magnetically soft film on the current strength in the system. Calculations show that there is a critical value of the current at which the magnetization sign of the controlled film changes. The magnetization versus current plot is stepwise. The change in the magnetization sign is due to an increase in the polarization of the electron gas. The plot of electron gas polarization versus current is also stepwise.

The writing performance of the easy-cone magnetic tunnel junction (MTJ) and perpendicularly magnetized MTJ (pMTJ) under various temperatures was investigated based on the macrospin model. When the temperature is changed from 273 K to 373 K, the switching current density of the pMTJ changes by 56%, whereas this value is only 8% in the easy-cone MTJ. Similarly, the temperature-induced variation of the switching delay is more significant in the pMTJ. This indicates that the easy-cone MTJ has a more stable writing performance under temperature variations, resulting in a wider operating temperature range. In addition, these two types of MTJs exhibit opposite temperature dependence in the current overdrive and write error rate. In the easy cone MTJ, these two performance metrics will reduce as temperature is increased. The results shown in this work demonstrate that the easy-cone MTJ is more suitable to work at high temperatures compared with the pMTJ. Our work provides a guidance for the design of STT-MRAM that is required to operate at high temperatures.

We derive a unified theory of spin and charge degrees of freedom in a ferromagnet. The spin-transfer torque and spin electromotive force are examined from the coarse-grained perspective of collective coordinates. The resulting equations of motion reflect a balance of conservative, gyroscopic (Berry-phase), and dissipative forces. We then expand the space of collective coordinates by adding the electric charge. The adiabatic spin-transfer torque and spin electromotive force (emf) turn out to be a gyroscopic force; their nonadiabatic counterparts are a dissipative force.

Dynamic simulations of spin-transfer and spin-orbit torques are increasingly important for a wide range of spintronic devices including magnetic random access memory, spin-torque nano-oscillators and electrical switching of antiferromagnets. Here we present a computationally efficient method for the implementation of spin-transfer and spin-orbit torques within the Landau-Lifshitz-Gilbert equation used in micromagnetic and atomistic simulations. We consolidate and simplify the varying terminology of different kinds of torques into a physical action and physical origin that clearly shows the common action of spin torques while separating their different physical origins. Our formalism introduces the spin torque as an effective magnetic field, greatly simplifying the numerical implementation and aiding the interpretation of results. The strength of the effective spin torque field unifies the action of the spin torque and subsumes the details of experimental effects such as interface resistance and spin Hall angle into a simple transferable number between numerical simulations. We present a series of numerical tests demonstrating the mechanics of generalised spin torques in a range of spin-tronic devices. This revised approach to modelling spin-torque effects in numerical simulations enables faster simulations and a more direct way of interpreting the results, and thus it is also suitable to be used in direct comparisons with experimental measurements or in a modelling tool that takes experimental values as input.

Spin-transfer torque (STT) and spin-orbit torque (SOT) are spintronic phenomena allowing magnetization manipulation using electrical currents. Beyond their fundamental interest, they allow developing new classes of magnetic memories and logic devices, in particular based on domain wall (DW) motion. In this work, we report the study of STT-driven DW motion in ferrimagnetic manganese nickel nitride (Mn4-xNixN) films, in which magnetization and angular momentum compensation can be obtained by the fine adjustment of the Ni content. Large domain wall velocities, approaching 3000 m/s, are measured for Ni compositions close to the angular momentum compensation point. The reversal of the DW motion direction, observed when the compensation composition is crossed, is related to the change of direction of the angular momentum with respect to that of the spin polarization. This is confirmed by the results of ab initio band structure calculations.

Spin currents can exert spin-transfer torques on magnetic systems even in the limit of vanishingly small net magnetization, as recently shown for antiferromagnets. Here, we experimentally show that a spin-transfer torque is operative in a macroscopic ensemble of weakly interacting, randomly magnetized Co nanomagnets. We employ element- and time-resolved X-ray ferromagnetic resonance (XFMR) spectroscopy to directly detect subnanosecond dynamics of the Co nanomagnets, excited into precession with cone angle ≳0.003° by an oscillating spin current. XFMR measurements reveal that as the net moment of the ensemble decreases, the strength of the spin-transfer torque increases relative to those of magnetic field torques. Our findings point to spin-transfer torque as an effective way to manipulate the state of nanomagnet ensembles at subnanosecond time scales.

Domain wall motion along ferrimagnets is evaluated using micromagnetic simulations and a collective-coordinates model, both considering two sublattices with independent parameters. Analytical expressions are derived for strips on top of either a heavy metal or a substrate with negligible interfacial Dzyaloshinskii-Moriya interaction. The work focuses its findings in this latter case, with a field-driven domain wall motion depicting precessional dynamics which become rigid at the angular momentum compensation temperature, and a current-driven dynamics presenting more complex behavior, depending on the polarization factors for each sublattice. Importantly, our analyses provide also novel interpretation of recent evidence on current-driven domain wall motion, where walls move either along or against the current depending on temperature. Besides, our approach is able to substantiate the large non-adiabatic effective parameters found for these systems.

Currently double-interface magnetic tunnel junctions (MTJs) have been developed for enhancing the thermal stability barrier at the nanoscale technology node. Dzyaloshinskii-Moriya interaction (DMI) inevitably exists in such devices due to the use of the heavy-metal/ferromagnet structures. Previous studies have demonstrated the detrimental effect of DMI on the conventional single-interface spin-transfer torque (STT) MTJs. Here, in this work, we will prove that the detrimental effect of DMI could be almost eliminated in the double-interface STT-MTJ. This conclusion is attributed to the suppressing effect of Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction on the DMI. Detailed mechanisms are analyzed based on the theoretical models and micromagnetic simulation results. Our work highlights the importance of appropriately controlling the DMI in the composite free layer of the double-interface STT-MTJ.