Efficient current-induced spin torques and field-free magnetization switching in a room-temperature van der Waals magnet.

The discovery of magnetism in van der Waals (vdW) materials has established unique building blocks for the research of emergent spintronic phenomena. In particular, owing to their intrinsically clean surface without dangling bonds, the vdW magnets hold the potential to construct a superior interface that allows for efficient electrical manipulation of magnetism. Despite several attempts in this direction, it usually requires a cryogenic condition and the assistance of external magnetic fields, which is detrimental to the real application. Here, we fabricate heterostructures based on Fe3GaTe2 flakes that have room-temperature ferromagnetism with excellent perpendicular magnetic anisotropy. The current-driven nonreciprocal modulation of coercive fields reveals a high spin-torque efficiency in the Fe3GaTe2/Pt heterostructures, which further leads to a full magnetization switching by current. Moreover, we demonstrate the field-free magnetization switching resulting from out-of-plane polarized spin currents by asymmetric geometry design. Our work could expedite the development of efficient vdW spintronic logic, memory, and neuromorphic computing devices.

Electrically programmable magnetic coupling in an Ising network exploiting solid-state ionic gating.

Two-dimensional arrays of magnetically coupled nanomagnets provide a mesoscopic platform for exploring collective phenomena as well as realizing a broad range of spintronic devices. In particular, the magnetic coupling plays a critical role in determining the nature of the cooperative behavior and providing new functionalities in nanomagnet-based devices. Here, we create coupled Ising-like nanomagnets in which the coupling between adjacent nanomagnetic regions can be reversibly converted between parallel and antiparallel through solid-state ionic gating. This is achieved with the voltage-control of the magnetic anisotropy in a nanosized region where the symmetric exchange interaction favors parallel alignment and the antisymmetric exchange interaction, namely the Dzyaloshinskii-Moriya interaction, favors antiparallel alignment of the nanomagnet magnetizations. Applying this concept to a two-dimensional lattice, we demonstrate a voltage-controlled phase transition in artificial spin ices. Furthermore, we achieve an addressable control of the individual couplings and realize an electrically programmable Ising network, which opens up new avenues to design nanomagnet-based logic devices and neuromorphic computers.

Observation of the Orbital Rashba-Edelstein Magnetoresistance.

We report the observation of magnetoresistance (MR) that could originate from the orbital angular momentum (OAM) transport in a permalloy (Py)/oxidized Cu (Cu^{*}) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The angular dependence of the MR depends on the relative angle between the induced OAM and the magnetization in a similar fashion as the spin Hall magnetoresistance. Despite the absence of elements with large spin-orbit coupling, we find a sizable MR ratio, which is in contrast to the conventional spin Hall magnetoresistance which requires heavy elements. Through Py thickness-dependence studies, we conclude another mechanism beyond the conventional spin-based scenario is responsible for the MR observed in Py/Cu^{*} structures-originated in a sizable transport of OAM. Our findings not only suggest the current-induced torques without using any heavy elements via the OAM channel but also provide an important clue towards the microscopic understanding of the role that OAM transport can play for magnetization dynamics.

Magnetic phase diagram of CrPS4 and its exchange interaction in contact with NiFe.

The magnetic phase diagram of the two-dimensional van der Waals magnet CrPS4 and the exchange bias effect of CrPS4 in contact with NiFe film have been investigated. Based on the magnetic measurements, we figure out the relatively low spin-flop field and spin-flip field for CrPS4, both of the spin transition phenomena are strongly affected by the temperature. The perpendicular exchange bias effect is studied in CrPS4 single-crystal flake covered with 5 nm NiFe. Meanwhile, the variation of the cooling field has a great influence on the exchange bias field and coercivity, which is mainly attributed to the competition between the Zeeman energy and the exchange coupling at the interface as well as the formation of the multi-domain state.

Spin switching temperature modulated by the magnetic field and spontaneous exchange bias effect in single crystal SmFeO3.

The spin switching and exchange bias effect were investigated in the rare earth orthoferrite SmFeO3 composed of two antiferromagnetically coupled sublattices Sm3+ and Fe3+ with canted ferromagnetic moments and a temperature induced spin switching in single crystal SmFeO3 was observed. The spin switching temperature was found to be modulated by exerting different magnetic fields below the compensation temperature ([Formula: see text]). This effect could be explained as the changes of energy barrier related to the magnetization direction under different magnetic fields. In the meantime, the coercivity displayed strong dependence on the maximum applied magnetic fields in the hysteresis measurement. In addition, spontaneous exchange bias effect (EB) was observed with the largest EB field value of 1.2 T, and the EB field changed its sign across the compensation point. Our results indicate that the magnetic properties of SmFeO3 can be strongly affected and controlled by the temperature or the applied magnetic field during the measurement process, and it might lead to novel applications in magneto-optics, ultrafast switching, and magnetic sensing devices.