Ferrimagnets for spintronic devices: From materials to applications

Abstract

Spintronic devices use spin instead of charge to process information and are widely considered as promising candidates for next-generation electronic devices. In past decades, the main motivation in spintronics has been to discover new mechanisms and novel material systems to improve both device performance and the application prospects of spintronics. Recently, researchers have found that ferrimagnetic materials—in which sublattices are coupled antiferromagnetically—offer an emerging platform for realizing high-density, high-speed, and low-power-consumption memory and logic functions. Within such a ferrimagnetic class, vanishing magnetization and ultrafast magnetic dynamics can be achieved by adjusting chemical composition and temperature, among other parameters. Meanwhile, unlike for antiferromagnets, conventional electrical read–write methods remain suitable for ferrimagnets, which is beneficial for applications. In this review, an abundant class of ferrimagnets including oxides and alloys is surveyed, and unique magnetic dynamics and effective methods for manipulating the magnetic states of ferrimagnets are discussed. Finally, novel storage and computing devices based on ferrimagnets are considered, as there are some challenges to be addressed in future applications of ferrimagnets.

Dirac Half-Semimetallicity and Antiferromagnetism in Graphene Nanoribbon/Hexagonal Boron Nitride Heterojunctions

“…In the latter state, the magnetic moments at the edges of the nanoribbon retain an antiparallel orientation, but their difference in magnitude results in a global spin polarization. 68 This is opposed to hydrogen-terminated ZGNRs, where the antiferromagnetic and spin-degenerate ground state is unchanged upon charge doping due to the spin-degeneracy of the band structure (Supporting Note S13). Embedding ZGNRs into an hBN matrix is thus an effective strategy to achieve the electrical control of their magnetism.…”

“…Overall, as depicted in Figure c, charge doping in ZGNR/ h BN heterojunctions drives a transition from an antiferromagnetic ground state, where the magnetic moments at the two edges of the nanoribbon feature an antiparallel orientation and equal magnitude, to a ferrimagnetic ground state. In the latter state, the magnetic moments at the edges of the nanoribbon retain an antiparallel orientation, but their difference in magnitude results in a global spin polarization . This is opposed to hydrogen-terminated ZGNRs, where the antiferromagnetic and spin-degenerate ground state is unchanged upon charge doping due to the spin-degeneracy of the band structure (Supporting Note S13).…”

Field-Free Spin–Orbit Torque-Induced Magnetization Switching in the IrMn/CoTb Bilayers with a Spontaneous In-Plane Exchange Bias

“…Current-induced magnetization switching driven by the spin torque effect in magnetic films has stimulated great interest because it can be potentially used in information storage devices. , In comparison with the spin transfer torque (STT) effect, which has already been commercialized in random access memory (MRAM), the spin–orbit torque (SOT) effect allows for decoupling the write and read current paths and thus has obvious superiority over STT . So far, perpendicular magnetization switching has been accomplished in the ferromagnet (FM), antiferromagnet (AFM), and ferrimagnet (FiM) by SOT generated from the spin current. − However, the perpendicular magnetizations are hard to switch without the assistance of an in-plane auxiliary magnetic field because the polarization of the spin current is commonly in the film plane in terms of the Rashba–Edelstein effect or spin Hall effect. − So far, people have made many attempts to realize field-free magnetization switching in spintronic devices by utilizing SOT. For example, some low symmetric alloys (e.g., Mn 2 Au and CuPt) can generate an out-of-plane polarized spin current, which can reverse the perpendicular magnetizations without a magnetic field.…”

“…19,20 Rare-earth transition metal (RE-TM) alloys (e.g., CoTb) are a representative kind of FiM materials, which have great usage in spintronic devices. 4,21,22 As a ferrimagnet, the magnetizations of RE and TM couple antiferromagnetically, and its net moment can be very small, producing a weak stray field, thus being favorable for high-density information storage. The magnetism of the RE-TM alloy is determined by the competition between the RE and TM sublattices, and strong perpendicular magnetic anisotropy (PMA) can be obtained and kept in a wide range of temperatures or compositions.…”

Manipulation of Spin–Orbit Torque in Tungsten Oxide/Manganite Heterostructure by Ionic Liquid Gating and Orbit Engineering

“…Charge current could be converted to spin current via the spin Hall effect (SHE) or Rashba-Edelstein effect (REE) in some heavy metals or topological insulators based on spin–orbit coupling (SOC) − and thereby exert a spin–orbit torque (SOT) on the adjacent magnetic layer. − The SOT could be employed to switch the magnetization and drive the magnetic textures (domain wall or skyrmion) motion, which exhibits enormous potential in the application of information storage and computing. , Controlling and enhancing the SOT has become one of the core topics in spintronic devices, and various strategies such as alloying, − oxidation, , and inserting intercalation , have been developed to achieve these goals. As SOC arises from the interaction between the electron’s spin and its orbital motions, the orbit degree of freedom should have a pronounced impact on the generation of spin current and SOT .…”