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.

In this study, the magnetic properties, coercivity mechanism, and magnetization reversal process were investigated for Ce-(Y)-Pr-Fe-B films. After the addition of Y and subsequent heating treatment, the formations of REO (RE ≡ Ce and Pr) and REFe₂ (RE ≡ rare earths) phases are inhibited, and the microstructure of Ce-Y-Pr-Fe-B film is optimized. Meanwhile, the coercivity and the squareness of the hysteresis loop are significantly improved. The coercivity mechanism of Ce-Y-Pr-Fe-B film is determined to be a mixture of nucleation and pinning mechanisms, but dominated by the nucleation mechanism. The demagnetization results show that the nucleation of reversal magnetic domains leads to irreversible reversal. Our results are helpful to understand the coercivity mechanism and magnetization reversal of permanent magnetic films with multi-main phases.

It is crucial to better understand the magnetization reversal process between soft and hard magnets and to achieve a high maximum energy product in thick composite multilayers. In this study, we find that the exchange interactions dominate in soft–hard-magnetic composite bilayers, while dipole interactions are predominant in soft–hard-magnetic composite trilayers. Based on the first-order reversal curve, magnetization reversal models are developed for both the thick composite bilayer and trilayer. Dipole interactions play an important role in the long range, resulting in higher coercivity and remanence in the thick trilayer. A multilayer in a stacked trilayer structure is achieved, which is composed of thick films with a perpendicular magnetic anisotropy at a thickness of up to 16 μm. The enhanced dipole interactions lead to a remanent polarization of 1 T and a maximum energy product of 22.5 MGOe. This work contributes to the preparation of thick films with a high maximum energy product for applications in magnetic microelectromechanical systems.