The ability to achieve perpendicular magnetization switching via spin-orbit torques (SOTs) is a critical advance for the development of the next generation of spintronic applications. However, the use of an external magnetic field to break the mirror symmetry is typically required to facilitate current-induced magnetization switching, which poses a significant challenge for practical implementation. Here, we demonstrate the field-free magnetization switching in the Y3Fe5O12 (YIG)/Pt heterostructure. This is achieved by introducing a lateral structure asymmetry in our devices, which can lead to an out-of-plane effective field. Our results provide an alternative solution for achieving field-free magnetization switching in nanoscale ferrimagnet-based heterostructures, thereby advancing the development of emerging SOT-based devices.

Spin–orbit torque (SOT) induced magnetization switching in an energy-efficient and fast way has exhibited great application potential in next generation magnetic memories. However, a complicated layer structure is usually needed to break the mirror symmetry for achieving SOT induced field-free magnetization switching. Here, we report a sizeable field-free magnetization switching through large out-of-plane SOT in the chemically disordered A1-CoxPt100−x single layers within a Co composition range from 40 to 70. The largest absolute out-of-plane SOT efficiency is found at its equiatomic concentration (Co50Pt50), in which the absolute in-plane SOT efficiency also reaches the maximum value, 22.7 Oe/107 A cm−2. We further demonstrate that the symmetry dependence of field-free magnetization switching might arise from the chemically ordered L11-CoPt nano-scaled platelets formed during the sample deposition. We expect that the experimental identification of the field-free magnetization switching in the ferromagnetic CoPt single layer is desirable to simplify the applications of spin logic devices.

Achieving effective manipulation of perpendicular exchange bias effect remains an intricate endeavor, yet it stands a significance for the evolution of ultra-high capacity and energy-efficient magnetic memory and logic devices. A persistent impediment to its practical applications is the reliance on external magnetic fields during the current-induced switching of exchange bias in perpendicularly magnetized structures. This study elucidates the achievement of a full electrical manipulation of the perpendicular exchange bias in the multilayers with an ultrathin antiferromagnetic layer. Owing to the anisotropic epitaxial strain in the 2-nm-thick IrMn3 layer, the considerable exchange bias effect is clearly achieved at room temperature. Concomitantly, a specific global uncompensated magnetization manifests in the IrMn3 layer, facilitating the switching of the irreversible portion of the uncompensated magnetization. Consequently, the perpendicular exchange bias can be manipulated by only applying pulsed current, notably independent of the presence of any external magnetic fields.

The dependence of perpendicular magnetic anisotropy (PMA) on the MgO thickness in Cr/CoFeB/MgO/Ta films has been experimentally investigated. A clear PMA is observed in the as-deposited samples with 1.8 nm MgO while no as-deposited PMA is shown in those with 4.0 nm MgO. This may be attributed to the moderate oxidation degree of CoFeB and larger interfacial anisotropy energy density K i to overcome the volume magnetic anisotropy and demagnetization field. On the contrary, samples with 4.0 nm MgO demonstrate PMA only after annealing, which might be due to the oxygen and boron diffusion during the annealing process. These results would provide a method to optimize the design of CoFeB/MgO structures on 3d metals for future applications in perpendicular magnetic devices.

The interlayer coupling and magnetization reversal behaviors in NiFe/NiO/NiFe trilayers were investigated using polarized neutron reflectivity and Monte Carlo (MC) simulations. Our results reveal that the shape of NiFe loops transitions from square to tilted as the NiO thicknesses decrease, indicating changes in the direction of NiFe layer’s easy axis. This phenomenon can be attributed to variations occurring at NiO/NiFe interfaces for different NiO layer thicknesses. With thin NiO layer, interdiffusion at the NiO/NiFe interfaces leads to frustrated coupling, resulting in a noncollinear interlayer coupling. This observation is supported by MC simulations. Conversely, hardly any coupling frustration is observed for the sample with a thick NiO layer. Our findings propose a novel way to tailor the interlayer coupling through interface engineering.

Field-free switching of a perpendicularly magnetized heavy metal/ferromagnetic metal bilayer or single alloy layer through spin-orbit torque (SOT) provides a potential way for next-generation spintronic devices with fast speed and high efficiency. Here, a sizable symmetry dependence of field-free magnetization switching via an out-of-plane torque in CoxPt100-x single layers is reported. It is found that the sign of in-plane SOT in CoxPt100-x when x <= 25 is positive. However, it changes to negative when x > 25, while the out-of-plane SOT changes its sign when x > 30. The polarized neutron reflectometry measurement further suggests an interface layer with rich Pt content near the substrate, which could have a strong interface effect on the out-of-plane SOT. The sign of the out-of-plane SOT, and then the polarity of the field-free magnetization switching, is determined by the competition between the out-of-plane torques arising from the bulk and interface parts in the CoxPt100-x single layers. It is expected that such interface effect of the out-of-plane torque is desirable to the applications in spin logic devices using symmetry dependence of field-free magnetization switching in the ferromagnetic CoPt single layers.

Antiferromagnetic (AFM) skyrmions are magnetic vortices composed of antiparallell-aligned neighboring spins. In stark contrast to conventional skyrmions based on ferromagnetic order, AFM skyrmions have vanished stray fields, higher response frequencies, and rectified translational motion driven by an external force. Therefore, AFM skyrmions promise highly efficient spintronics devices with high bit mobility and density. Nevertheless, the experimental realization of intrinsic AFM skyrmions remains elusive. Here, we show that AFM skyrmions can be nucleated via interfacial exchange coupling at the surface of a room-temperature AFM material, IrMn, exploiting the particular response from uncompensated moments to the thermal annealing and imprinting effects. Further systematic magnetic characterizations validate the existence of such an AFM order at the IrMn/CoFeB interfaces. Such AFM skyrmions have a typical size of 100 nm, which presents pronounced robustness against field and temperature. Our work opens new pathways for magnetic topological devices based on AFM skyrmions.

AbstractThe energy‐efficient spin‐orbit torque (SOT) based devices are essential for future memory and logic technologies. To realize a deterministic switching, an external in‐plane magnetic field is usually needed to break the symmetry, which becomes an obstacle for device applications. Here, a field‐free switching in a perpendicularly magnetized yttrium iron garnet covered with an oblique deposited Pt with nitrogen incorporation is demonstrated. The spin‐orbit torque efficiency is enhanced with the increasing incorporation ratio of nitrogen in Pt. The maximum effective spin Hall angle of Pt(N) can reach 0.113, which is almost two times larger than that of pure Pt in Pt/YIG. Meanwhile, the switching current density is reduced with the incorporation of nitrogen. These findings open a route toward high‐efficiency SOT driven spintronic devices based on magnetic insulators.

Due to the strong interlayer coupling between multiple degrees of freedom, oxide heterostructures usually produce distinct interfacial phases with unexpected functionalities. Here, we report on the realization of quasi-two-dimensional ferromagnetic state in ultrathin La0.7Sr0.3MnO3 (LSMO) layer down to two unit cells (u.c.), being sandwiched by the planar infinite-layer structured SrCuO2 layers (P-SCO). We find the LSMO/P-SCO interface coupling has greatly suppressed the magnetic dead layer of LSMO, resulting in an emergent interfacial ferromagnetic phase. Thus, robust ferromagnetic order can be maintained in the 2 u.c.-thick LSMO layer (∼7.7 Å), showing a Curie temperature of ∼260 K and remarkable perpendicular magnetic anisotropy. X-ray absorption spectra reveal notable charge transfer from Mn to Cu at the interface, and thus, resulted preferential d3z2−r2 orbital occupation for interfacial Mn ions plays an important role in the inducing of perpendicular magnetic anisotropy in quasi-two-dimensional LSMO layer. Our work demonstrates a unique approach for tuning the properties of oxides via an interface engineering of oxygen coordination in perovskite/infinite-layer heterostructures.

Manipulating spin polarization orientation is challenging but crucial for field-free spintronic devices. Although such manipulation has been demonstrated in a limited number of antiferromagnetic metal-based systems, the inevitable shunting effects from the metallic layer can reduce the overall device efficiency. In this study, we propose an antiferromagnetic insulator-based heterostructure NiO/Ta/Pt/Co/Pt for such spin polarization control without any shunting effect in the antiferromagnetic layer. We show that zero-field magnetization switching can be realized and is related to the out-of-plane component of spin polarization modulated by the NiO/Pt interface. The zero-field magnetization switching ratio can be effectively tuned by the substrates, in which the easy axis of NiO can be manipulated by the tensile or compressive strain from the substrates. Our work demonstrates that the insulating antiferromagnet based heterostructure is a promising platform to enhance the spin-orbital torque efficiency and achieve field-free magnetization switching, thus opening an avenue towards energy-efficient spintronic devices.

Spin obit torque (SOT) driven magnetizationswitching has beenused widely for encoding consumption-efficient memory and logic. However,symmetry breaking under a magnetic field is required to realize thedeterministic switching in synthetic antiferromagnets with perpendicularmagnetic anisotropy (PMA), which limits their potential applications.Herein, we report all electric-controlled magnetization switchingin the antiferromagnetic Co/Ir/Co trilayers with vertical magneticimbalance. Besides, the switching polarity could be reversed by optimizingthe Ir thickness. By using the polarized neutron reflection (PNR)measurements, the canted noncollinear spin configuration was observedin Co/Ir/Co trilayers, which results from the competition of magneticinhomogeneity. In addition, the asymmetric domain walls demonstratedby micromagnetic simulations result from introducing imbalance magnetism,leading to the deterministic magnetization switching in Co/Ir/Co trilayers.Our findings highlight a promising route to electric-controlled magnetismvia tunable spin configuration, improve our understanding of physicalmechanisms, and significantly promote industrial applications in spintronicdevices.

Chiral magnetism defines the spin structure sense of rotation in magnetic films and stabilized by the interfacial Dzyaloshiniskii-Moriya interaction (DMI), which can be used to generate the chiral nature of magnetic textures like spin spirals and skyrmions. Here, the direct evidence of the interlayer DMI was observed at room temperature, by designing the synthetic system with a ferromagnet/insulating spacer/ferromagnet structure whose magnetic chirality can be effectively manipulated between ferromagnetic coupling and antiferromagnetic coupling by changing spacer thickness. The interlayer DMI breaks the symmetry of the magnetic reversal process, leading to chiral exchange-biased Hall loops, where the noncollinear magnetic states were systematically characterized and quantified by using polarized neutron reflectometry (PNR). PNR results indicate that the maximum angle of the canted magnetic moments for ferromagnetic coupling can reach as high as 11.5 degrees, which is stronger than that for antiferromagnetic coupling, suggesting the higher energy excitation of magnetic chirality. This canted spin structure is verified by first-principles calculation. Our findings should be greatly useful for the interfacial design of spintronic devices to control and tailor the magnetic chirality for the formation of the spin texture in high-density memory.