Search

Chirality-induced spin selectivity (CISS) allows for the generation of spin currents without the need for ferromagnets or external magnetic fields, enabling innovative spintronic device designs. One example is a chiral spin valve composed of ferromagnetic and chiral materials, in which the resistance depends on both the magnetization direction of the ferromagnet and the chirality of the chiral material. So far, chiral spin valves have predominately employed chiral organic molecules, which have limited device applications. Chiral perovskites, which combine the properties of inorganic perovskites with chiral organic molecules, provide an excellent platform for exploring CISS-based devices. However, previous chiral perovskite-based spin valves exhibited magnetoresistance (MR) only at low temperatures. Here, we report room temperature MR in a chiral spin valve consisting of chiral perovskites/AlOx/perpendicular ferromagnet structures. It is observed that the chiral MR increases with rising temperature, suggesting the crucial role of phonon-induced enhancement of spin–orbit coupling in CISS in our device. Furthermore, we enhanced the chiral MR by introducing chiral molecules with amplified chirality. This highlights the potential of chirality engineering to improve CISS and the associated chiral MR, thereby opening possibilities for chiral spin valves tailored for cutting-edge spintronic applications.

Abstract Current-induced spin torques enable the electrical control of the magnetization with low energy consumption. Conventional magnetic random access memory (MRAM) devices rely on spin-transfer torque (STT), this however limits MRAM applications because of the nanoseconds incubation delay and associated endurance issues. A potential alternative to STT is spin-orbit torque (SOT). However, for practical, high-speed SOT devices, it must satisfy three conditions simultaneously, i.e., field-free switching at short current pulses, short incubation delay, and low switching current. Here, we demonstrate field-free SOT switching at sub-ns timescales in a CoFeB/Ti/CoFeB ferromagnetic trilayer, which satisfies all three conditions. In this trilayer, the bottom magnetic layer or its interface generates spin currents with polarizations in both in-plane and out-of-plane components. The in-plane component reduces the incubation time, while the out-of-plane component realizes field-free switching at a low current. Our results offer a field-free SOT solution for energy-efficient scalable MRAM applications.

Abstract Physical unclonable functions (PUFs), which exploit uncontrollable and unpredictable randomness of materials or devices, have been investigated as a hardware‐based security primitive owing to their robustness against adversarial attacks. Spin–orbit torque (SOT) switching is one of the promising techniques for PUF applications because it can provide randomness by the stochastic switching distribution of perpendicular magnetization. In this study, the improvement in the reliability of SOT‐based PUFs against external magnetic fields with write‐back operation (WBO) is demonstrated. A PUF consisting of 8 × 4 array Hall‐bar devices with a Ta/CoFeB/MgO structure is fabricated, where the random distribution of the SOT switching current serves as an entropy source. However, the information stored in the PUF is easily modified by the application of an external magnetic field. To improve the robustness against magnetic fields, a WBO is introduced that applies an additional current to saturate the magnetization in either the upward or downward direction depending on the magnetic state. As a result, the SOT‐based PUF maintains an entropy value close to unity under a magnetic field of up to the coercive field of the CoFeB layer. Furthermore, the WBO provides a digitalized output, which potentially reduces peripheral circuitry such as analog‐to‐digital converters.

Manipulation of the magnetization is of major importance in spintronics. The authors demonstrate that an electric field triggers a transverse flow of orbital moment: the so-called orbital Hall effect. This enables the efficient magnetization control, holding the promise for fast and miniaturized memories and sensors.

Antiferromagnets have great promise for spin-based information processing, offering both high operation speed, and an immunity to stray fields. Here, Kang et al demonstrate electrical manipulation of the exchange-bias, without the need for a heavy metal layer.

Abstract Interface‐generated spin currents in ferromagnet (FM)/nonmagnet (NM) structures provide both in‐plane and out‐of‐plane spin–orbit torques (SOTs), enabling the field‐free switching of perpendicular magnetization of the other FM layer in magnetic trilayers. In this study, the NM thickness dependence of interface‐generated spin currents and associated SOTs in FM/Ti/CoFeB trilayers is investigated. In such magnetic trilayers, it is known that the in‐plane SOT results from the spin–orbit filtering of the interface‐generated spin current, while the out‐of‐plane SOT is due to the spin–orbit precession. These results show that the polarity of current‐induced magnetization switching under an in‐plane magnetic field reverses with increasing Ti thickness. This indicates that the sign of the in‐plane SOT depends on the current distribution between the bottom FM and Ti layers. On the other hand, field‐free switching occurs only for a Ti thickness of up to ≈4 nm, and the same polarity is retained, demonstrating that out‐of‐plane SOT is governed by the charge current flowing near the interface. These results suggest that field‐free switching efficiency can be enhanced by engineering the relative conductance of the FM/NM bilayers to constructively combine in‐plane and out‐of‐plane SOTs caused by interface‐generated spin currents.