Zhiyong Quan

Orbital current in light metals has attracted considerable attention as an alternative tool to switch the magnetization of ferromagnets. However, the manipulation of orbital torque efficiency, which is a key aspect of novel spin-orbitronic devices, remains a challenge. Here, the reversible modulation of orbital torque at room temperature is demonstrated in perpendicularly magnetized Ta/Pt/Co/Cu–CuOx/MoOx Hall bar devices. By applying a negative electric field, the orbital torque efficiency of a device with a Cu–CuOx thickness of 3 nm can be significantly enhanced by a factor of ∼4.64. This outstanding result is attributed to the applied electric fields driving the migration of oxygen ions, which controls the distance between the Cu/CuOx interface and the Co layer, as well as the formation or reduction of an antiferromagnetic CoOx layer at the Co surface. Consequently, the injection efficiency of the orbital current is controlled. In addition, the critical magnetization switching current density is reduced by ∼36% by applying an electric field. These findings provide a pathway for implementing electrically driven magnetization switching in potential applications while also opening new avenues for the development of spin-orbitronic devices.

Magnetoresistance in the 2D ferromagnetic van der Waals (vdW) Fe ₃ GaTe ₂ (FGT) has emerged as a new frontier in spintronics, with particular interest paid to the antisymmetric magnetoresistance (AsMR) effect due to its potential to realize multi‐state memory, promising for constructing energy‐efficient memory devices. However, the mechanism underlying the room‐temperature AsMR remains unresolved. Herein, a structural design of two completely isolated FGT nanoflakes, combined with measurement approaches using swapping electrodes and flipping device orientations, was used to clarify the physics of room‐temperature AsMR in vdW ferromagnetic FGT‐based systems. The results show the unambiguous presence of room‐temperature AsMR with four distinct resistance states in the FGT/Pt Hall bar devices. Spin‐momentum locking is identified in the vdW FGT‐based heterostructures and found to be responsible for the observed room‐temperature AsMR. The special design and magneto‐electric transport measurements rule out the magnetic domain wall–induced circulating currents and interface pinning as possible origins of AsMR. Further confirmation of this physical mechanism is provided by the distinctive configuration of two FGT nanoflakes separated by a micrometer‐scale gap. Overall, the physical mechanism of room‐temperature AsMR in vdW FGT/Pt heterostructures is experimentally confirmed, opening new avenues for low‐power room‐temperature spintronic devices.

Orbital torque (OT) harnesses orbital currents to electrically encode spin states, offering a promising route toward low-power spintronic devices. However, the microscopic mechanisms governing OT efficiency remain elusive. Here, we employ Ru, a light metal possessing positive spin and orbital Hall conductivities, as an orbital source to switch perpendicularly magnetized [Co/Pt]3 multilayers with a negative orbital-to-spin conversion coefficient. This configuration enables a clear separation between OT and conventional spin–orbit torque. We find that the OT efficiency decreases monotonically with increasing Ru thickness, confirming an interfacial rather than bulk origin of the orbital current. Notably, robust magnetization switching persists even for a Ru thickness of only 1 nm, achieving a critical switching current density of 1.9 × 107 A/cm2, nearly half that of the heavy-metal Pt reference. These findings not only elucidate the physical mechanism of OT but also establish key design principles for the development of energy-efficient orbitronic memory devices.

轨道霍尔磁电阻效应是研究轨道流输运和轨道角动量-磁矩相互作用的有效手段，近年来引起研究者广泛关注.但轻金属/磁性材料异质结构中受限于轨道流-自旋流转换效率低，磁电阻数值普遍偏小.本文中，我们利用轻金属Cr的轨道霍尔效应提供轨道流，通过重金属Pt提升轨道流-自旋流转换效率，在垂直磁化Cr(t)/Co/Pt₃多层膜体系中获得室温下1.6×10^-3的轨道霍尔磁电阻，高出以前同类实验报道1个数量级.同时，利用Cr厚度与磁电阻变化关系拟合出Cr中轨道流扩散长度约为0.93 nm，远小于以前的实验报道.进一步，在Cr/Pt/Co/Pt多层膜中，利用重金属Pt插层提高轨道流-自旋流转换效率，通过轨道霍尔效应和自旋霍尔效应共同作用，有效提升体系磁电阻值达到4.5×10^-3.这些结果对理解轨道-磁序耦合机制以及发展低功耗自旋轨道电子器件提供重要实验依据.

Electric-field control of magnetization switching holds great promise for the development of spintronic devices due to its intrinsically low power consumption. Here, we demonstrate the efficient and reversible manipulation of field-free perpendicular magnetization switching through the electric-field driven migration of oxygen ions within the Pt/Co/CuOx/MoOx system. The antiferromagnetic CoO layer at the Co/CuOx interface modulated by the gate voltage provides an exchange bias field, enabling field-free current-driven magnetization switching. The field-free switching ratio can be effectively enhanced by applying a negative gate voltage, with the maximum value being 62.7%, which is five times larger than that in the initial state without applying gate voltage. The electric-field driven migration of oxygen ions, causing enhanced/reduced oxidation at the Co/CuOx interface, leads to the reversible tunability of the field-free perpendicular magnetization switching. These results offer an approach to effectively control perpendicular magnetization switching without the need for a magnetic field, holding significant implications for low-power spintronic applications.

Unraveling the mechanism behind bulk perpendicular magnetic anisotropy (PMA) in amorphous rare earth-transition metal films has proven challenging. This is largely due to the inherent complexity of the amorphous structure and the entangled potential origins arising from microstructure and atomic structure factors. Here, we present an approach wherein the magneto-electric effect is harnessed to induce 90° switching of bulk PMA in Tb-Co films to in-plane directions by applying voltages of only -1.2 V. This manipulation is achieved by voltage-driven insertion of hydrogen atoms into interstitial sites between Tb and Co atoms, which serves as a perturbation to the local atomic structure. Using angle-dependent X-ray magnetic circular dichroism, we find that the anisotropy switching originates from the distortion of the crystal field around Tb, which reorients the alignment of Tb orbital moments. Initially aligned along Tb-Co bonding directions, the easy magnetization axis undergoes reorientation and switches by 90°, as substantiated by ab initio calculations. Our study not only concludes the atomic origin of Tb-Co atom bonding configuration in shaping bulk PMA but also establishes the groundwork for electrically programmable ferrimagnetic spintronics, such as controlling domain wall motion and programming artificial spin textures.

Current-induced spin–orbit torque (SOT) has attracted much attention due to its potential applications in energy-efficient logic, memory, and artificial neuron devices. In this work, we report an enhanced SOT efficiency in perpendicularly magnetized Pt/Sm/Co/Ta heterostructures by inserting a light rare-earth Sm layer with large spin–orbit coupling. A series of Ta/Pt/Sm/Co/Ta samples with the Sm layer thickness (tSm) of 0, 0.6, 1.2, and 1.6 nm were prepared using direct-current magnetron sputtering. Perpendicular magnetic anisotropy, SOT efficiency, and current-driven magnetization reversal were characterized using electrical transport methods based on the anomalous Hall effect. The experimental results indicated that the switching field and magnetic anisotropic field decreased monotonically with an increase in tSm, while the damping-like effective field and effective spin Hall angle (θSHeff) gradually increased. It demonstrates that interface modification with a Sm layer can improve the SOT efficiency and reduce the pinning potential barrier. Owing to the enhanced SOT and reduced pinning field, the critical switching current density (Jc) exhibits a steady decline when increasing tSm. In particular, the lowest Jc of approximately 7.83 × 106 A/cm2 was obtained when tSm was 1.6 nm. X-ray photoelectron spectroscopy revealed that electron transfer occurred between the Co, Pt, and Sm layers, which may be primarily responsible for the enhanced SOT by interface alloying to effectively strengthen the spin Hall effect of Sm and/or Pt. Our results provide a strategy for improving SOT efficiency and reducing Jc by interface alloying in SOT-based spintronic devices.

Orbital currents in light metals or metal oxides without the strong spin–orbit coupling have become an important means to achieve low-power magnetization switching in spin–orbitronic devices. The orbital magnetoresistance (OMR) originated from orbital current represents a useful strategy to explore the interaction between the orbital angular momentum (OAM) and the local magnetic moment. However, systematic research works on the enhancement of OMR and the mechanism of OAM transport are seldom reported. In this study, we report a synergistically enhanced magnetoresistance effect induced by spin and orbital currents in perpendicularly magnetized Pt/Co/Cu–CuOx systems. A maximum room temperature magnetoresistance of 0.38% was observed, exceeding the spin Hall magnetoresistance (SMR) of heavy metal-based heterostructures by one order of magnitude. The enhancement of magnetoresistance is attributed to the contributions from the OMR generated by the orbital Rashba effect at the Cu/CuOx interface and SMR induced by the spin Hall effect in heavy metal Pt. These results provide a pathway to understanding of the OAM transport in magnetic multilayer films and contribute to the design and realization of energy-efficient spin–orbitronic devices.

This study presents experimental evidence of the substantial modulation of ferromagnetism and spin–orbit torque (SOT) efficiency in a Ta/Pt/Co/Ta/In2Se3 heterostructure with perpendicular magnetic anisotropy through light irradiation. An increase in SOT efficiency of ∼20% and a reduction in critical switching current density of ∼52% were observed. The significant modulation primarily originates from the photostrictive effect of a van der Waals-layered ferroelectric In2Se3 layer, which is assisted by thermal effects under light irradiation. The present research provides a potential approach to modulating magnetism and SOT efficiency for energy-efficient spintronic devices.