Perpendicular Magnetic Anisotropy Systems Research Articles

Magnetization switching driven by spin current in a T-type ferromagnetic trilayer

The T-type CoFeB/spacer/CoFeB structure is a promising candidate for the development of perpendicular spin–orbit torque (SOT) magnetic random-access memory and other SOT devices. It consists of an in-plane magnetized layer, a perpendicularly magnetized layer, and a non-magnetic metal spacer that induces interlayer exchange coupling. By engineering the W spacer, this system achieves field-free SOT switching with a nearly 100% switching ratio. Furthermore, it realizes a high exchange coupling field of 255 Oe using a relatively thinner spacer thickness, enhancing the reliability and energy efficiency of SOT switching. Measurement of current switching probability suggests that this perpendicular magnetic anisotropy system may enable the implementation of probability-adjustable true random number generators in future applications. The T-type structures with strong interlayer coupling exhibit great potential for spintronic device applications.

Role of the chiral spin configuration in field-free spin–orbit torque-induced magnetization switching by a locally injected spin current

For deterministic magnetization switching by spin–orbit torque (SOT) in a perpendicular magnetic anisotropy system, an additional in-plane direction magnetic field is essential to break the lateral symmetry. Realizing chirality in a magnetic ordering system can be one approach for achieving asymmetry in the lateral direction for field-free magnetization switching. However, systematic analysis of the influence of the chiral spin system on deterministic switching is still scarce. We investigate the field-free SOT-induced magnetization switching by using a chiral spin configuration experimentally and theoretically with micromagnetic simulations. We designed a system in which only part of the ferromagnetic layer overlaps with the heavy metal layer in the Pt/Co/MgO structure. Therefore, a spin current exerts only on a local area of the ferromagnetic layer, which results in a Néel-type chiral spin configuration. The induced chiral spin configuration can be stabilized (or destabilized) depending on the sign of the interfacial Dzyaloshinskii–Moriya interaction and the direction of the current. The stabilized spin configuration plays a crucial role in the deterministic switching in the zero field. We expect our findings to widen the perspective on chirality-based all-electrical SOT device applications.

Abnormal peak of angular-dependent Hall effect as an indicator for skyrmion in perpendicular magnetic anisotropy system

The anomalous Hall effect (AHE) has been extensively studied in terms of its diverse and profound physics, but the AHE behavior under spatially rotated external fields has not been well understood yet. Here, we selected a traditional CoFeB-based multilayer film as the platform, and by continuously tuning its magnetic anisotropy, we have observed the progressively evolved angular-dependence of the AHE, in which an abnormal turning peak emerged in the case of moderate perpendicular magnetic anisotropy (PMA). By applying comprehensive micromagnetic simulations, a general model was established that can almost fully account for the existing trend of the angular AHE. The PMA magnitude, together with the multi-to-single domain transformation, determined the final behavior of the AHE at various magnetic-field-tilt angles. Notably, we identified a close relationship between the angular-Hall anomaly and formation of magnetic skyrmions, which can possibly offer an alternative method to detect the skyrmions.