Toward magnonic devices: The field of magnonics aims to use spin waves (SWs) and their associated quasiparticles—magnons—as carriers of information. Compared with the movement of charge in conventional electronics, a major advantage of SWs is reduced Joule heating. However, SWs are trickier to direct and control. Two groups now go a step further toward magnon-based devices. Han et al. show that in multilayer films, domain walls can be used to change the phase and magnitude of a spin wave. Wang et al. demonstrate how magnon currents can be used to switch the magnetization of an adjacent layer. Science , this issue p. 1121 , p. 1125

Current induced spin-orbit torques driven by the conventional spin Hall effect are widely used to manipulate the magnetization. This approach, however, is nondeterministic and inefficient for the switching of magnets with perpendicular magnetic anisotropy that are demanded by the high-density magnetic storage and memory devices. Here, we demonstrate that this limitation can be overcome by exploiting a magnetic spin Hall effect in noncollinear antiferromagnets, such as Mn₃Sn. The magnetic group symmetry of Mn₃Sn allows generation of the out-of-plane spin current carrying spin polarization collinear to its direction induced by an in-plane charge current. This spin current drives an out-of-plane anti-damping torque providing the deterministic switching of the perpendicular magnetization of an adjacent Ni/Co multilayer. Due to being odd with respect to time reversal symmetry, the observed magnetic spin Hall effect and the resulting spin-orbit torque can be reversed with reversal of the antiferromagnetic order. Contrary to the conventional spin-orbit torque devices, the demonstrated magnetization switching does not need an external magnetic field and requires much lower current density which is useful for low-power spintronics.

We report a breakthrough in the hardware implementation of energy-efficient all-spin synapse and neuron devices for highly scalable integrated neuromorphic circuits. Our work demonstrates the successful execution of all-spin synapse and activation function generator using domain wall-magnetic tunnel junctions. By harnessing the synergistic effects of spin-orbit torque and interfacial Dzyaloshinskii-Moriya interaction in selectively etched spin-orbit coupling layers, we achieve a programmable multi-state synaptic device with high reliability. Our first-principles calculations confirm that the reduced atomic distance between 5dand 3datoms enhances Dzyaloshinskii-Moriya interaction, leading to stable domain wall pinning. Our experimental results, supported by visualizing energy landscapes and theoretical simulations, validate the proposed mechanism. Furthermore, we demonstrate a spin-neuron with a sigmoidal activation function, enabling high operation frequency up to 20 MHz and low energy consumption of 508 fJ/operation. A neuron circuit design with a compact sigmoidal cell area and low power consumption is also presented, along with corroborated experimental implementation. Our findings highlight the great potential of domain wall-magnetic tunnel junctions in the development of all-spin neuromorphic computing hardware, offering exciting possibilities for energy-efficient and scalable neural network architectures.

A True Random Number Generator is an essential component in data encryption, hardware security, physical unclonable functions, and statistical analyses. Conventional CMOS devices usually exploit the thermal noise or jitter to generate randomness, which suffers from high energy consumption, slow bit generating rate, large area, and over-complicated circuit. In this mini review, we introduce the novel physical randomness generating mechanism based on the stochastic switching behavior of magnetic tunnel junctions. As compared to CMOS technologies, the random number generator based on spintronic devices can have many inherent advantages, such as simpler structure, compact area, higher throughput, and better energy-efficiency. Here, we review and compare various existing schemes at the device and circuit levels to achieve high performance magnetic tunnel junctions based on a True Random Number Generator. Future research trends and challenges are also discussed to stimulate more works in this area.