Alloying a heavy metal (HM) layer is a useful approach to enhance the current-spin converting efficiency ξ_SH while keeping a relatively low resistance for spin–orbit torque (SOT) based devices. In this work, we report the enhancement of ξ_SH and nonlinear modification of the Dzyaloshinskii–Moriya interaction (DMI) by alloying Pt with Cr in a Pt_100-xCr_x/Co/AlO_x trilayer. The maximum of ξ_SH is found at the composition of Pt₇₅Cr₂₅. At the compositions of Pt₇₅Cr₂₅ and Pt₅₀Cr₅₀, the DMI constant |D| is strongly shifted in the opposite sign, implying ferromagnetic coupling and antiferromagnetic coupling existing in the heavy metal layer can both influence the DMI. Finally, the current-driven switching behavior is observed by the magneto-optical effect. This work shows that adjusting the composition of the magnetic alloyed HM layer is an efficient approach to obtain an optimized SOT performance.

The spin-orbit-torque (SOT) device is a promising candidate for the next-generation magnetic random-access memory; however, the static in-plane field needed to induce deterministic switching is a main obstacle for its application in circuits. In this work, we employ the exchange coupling between the $\mathrm{Co}$/$\mathrm{Ni}$/$\mathrm{Co}$ trilayer and $\mathrm{Tb}$/$\mathrm{Co}$ multilayers in a device to form the domain wall (DW), by whose current-driven propagation the field-free magnetization switching is achieved. The SOT efficiency of the device is highly dependent on the chirality of the Néel-type DW. Meanwhile, the coexistence of two switching modes results in an asymmetric switching phase diagram. We find the competition between the uniform external field and the Dzyaloshinskii–Moriya interaction induces negative feedback to the pinning effect, resulting in a sharp switching process and straight DW profile. Finally, a synthetic antiferromagnetic device is investigated by experiment and micromagnetic simulation to verify the feasibility of using this proposal as the free layer of a magnetic tunneling junction.

A perpendicularly magnetized synthetic antiferromagnetic structure is a promising alternative to a single ferromagnetic layer in spintronic applications because of its low net magnetization and high thermal stability. In this work, the ferromagnetic layers in the synthetic antiferromagnetic structure are simplified to ‘soft’ Co₇₀Fe₃₀ layers with the aid of ultrathin Pt insert layers between the ferromagnetic layers and the exchange coupling Ru layer to lower the energy consumption. In the current-driven manipulation of the magnetization, asymmetric switching loops are observed, which originate from the edge domain walls induced by the growth of the electrode pads. The edge domain walls preserved beneath the electrode pad help the switching process skipping the nucleation stage, lowering the critical current density to the order of 10⁶ A cm⁻². The present work broadens the choice of ferromagnetic layers for building an SAF structure and highlights a new way to utilize the synthetic antiferromagnetic structure as a building block in low-energy-consuming spintronic devices.

Generally, the addition of the Dy element leads to a decrease of the saturation magnetization and the remanent magnetization in NdFeB films due to its antiferromagnetic coupling with Fe. However, in this study, upon increasing the ratio of Dy in the Nd–Dy diffusion layers of NdFeB thick films, the saturation magnetization has an anomalously slight enhancement, while the coercivity and remanent magnetization have a large enhancement. The increase of coercivity is attributed to the decoupling between Nd₂Fe₁₄B grains and the enhanced pinning effect. Microstructural analysis revealed a layered structure composed of spherical Nd₂Fe₁₄B grains at the location of the Dy diffusion layer, which is attributed to the Dy diffusion layer reacting with the region of Nd element aggregation during the annealing process, facilitating transformation into Nd₂Fe₁₄B grains. The increase of the proportion of Nd₂Fe₁₄B grains results in a slight enhancement of saturation magnetization. By this method, we obtained a high-performance anisotropic NdFeB thick film of 28.7 μm with a coercivity of 2.46 T and a surface field of 163 Oe. This work establishes a microscale growth model for NdFeB thick films and helps to prepare high-performance NdFeB thick films applicable directly to microelectromechanical systems.

The ability to efficiently manipulate magnetization is of great significance for practical applications of spin–orbit torque (SOT) devices. In this study, we report the voltage-controlled, field-free SOT switching in perpendicular magnetized Pt/Co/Ir/MgO structures with wedge iridium interlayers. The insertion of a thin iridium interlayer at ferromagnet/oxide can significantly reduce the perpendicular magnetic anisotropy depending on the Ir thickness. The wedging of the iridium layer breaks lateral structural symmetry, resulting in deterministic switching without the assistance of in-plane magnetic fields. In such a structure, the SOT critical switching currents are remarkably decreased by 29% when a positive 6 V gate voltage is applied. Further quantitative analysis shows that multiple factors contribute to the decrease in switching currents, including a 23% reduction in magnetic anisotropy energy, a reduction in nucleation field, and a minor enhancement in damping-like torque under gate voltage. Moreover, the probabilistic hindrance that gate voltage poses to field-free switching is revealed by the decrease in current-induced perpendicular effective fields from symmetry-breaking. Our research shows that energy-efficient SOT switching can be controlled by gating and offers insight into the mechanism behind voltage-gated SOT switching.

Magnetic properties and coercivity mechanism of an anisotropic Ce–Nd–Fe–B film with a high Ce content (70 at. % Nd is replaced by Ce) have been investigated. After grain boundary diffusion with Tb layers, an enhancement of coercivity from 4150 to 9250 Oe is observed. Combining the initial magnetization curves, micromagnetic theory, and in-siut observation of magnetic domains in the demagnetization process, it is confirmed that the coercivity mechanism for the high-Ce-content magnets is the mixed type dominated by the pinning mechanism. Moreover, as the thickness of the Tb diffusion layer increases, the pinning center of domain walls changes from narrow planar inhomogeneities to wide planar inhomogeneities. A growing role of pinning plays in determining the coercivity of samples with increasing the thickness of Tb layer due to the increase in magnetocrystalline anisotropy after Tb substitution in the RE₂Fe₁₄B phase. In addition, the CeFe₂ intergranular phase leads to the enhancement of coercivity due to decoupling the hard magnetic phase grains. Our results provide an insight into the coercivity mechanism of high-Ce-concentration Ce–Nd–Fe–B magnetic materials and promote the comprehension of the effect of Tb diffusion in the magnetization reversal process.