Ruderman-Kittel-Kasuya-Yosida-Type Interlayer Dzyaloshinskii-Moriya Interaction in Synthetic Magnets

Magneto-Ionic Engineering of Antiferromagnetically RKKY-Coupled Multilayers

Voltage-driven ion motion offers a powerful means to modulate magnetism and spin phenomena in solids, a process known as magneto-ionics, which holds great promise for developing energy-efficient next-generation micro- and nano-electronic devices. Synthetic antiferromagnets (SAFs), consisting of two ferromagnetic layers coupled antiferromagnetically via a thin non-magnetic spacer, offer advantages such as enhanced thermal stability, robustness against external magnetic fields, and reduced magnetostatic interactions in magnetic tunnel junctions. Despite its technological potential, magneto-ionic control of antiferromagnetic coupling in multilayers (MLs) has only recently been explored and remains poorly understood, particularly in systems free of platinum-group metals. In this work, room-temperature voltage control of Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions in Co/Ni-based SAFs is achieved. Transitions between ferrimagnetic (uncompensated) and antiferromagnetic (fully compensated) states is observed, as well as significant modulation of the RKKY bias field offset, emergence of additional switching events, and formation of skyrmion-like or pinned domain bubbles under relatively low gating voltages. These phenomena are attributed to voltage-driven oxygen migration in the MLs, as confirmed through microscopic and spectroscopic analyses. This study underscores the potential of voltage-triggered ion migration as a versatile tool for post-synthesis tuning of magnetic multilayers, with potential applications in magnetic-field sensing, energy-efficient memories and spintronics.

Asymmetric magnetization switching and programmable complete Boolean logic enabled by long-range intralayer Dzyaloshinskii-Moriya interaction

After decades of efforts, some fundamental physics for electrical switching of magnetization is still missing. Here, we report the discovery of the long-range intralayer Dzyaloshinskii-Moriya interaction (DMI) effect, which is the chiral coupling of orthogonal magnetic domains within the same magnetic layer via the mediation of an adjacent heavy metal layer. The effective magnetic field of the long-range intralayer DMI on the perpendicular magnetization is out-of-plane and varies with the interfacial DMI constant, the applied in-plane magnetic fields, and the magnetic anisotropy distribution. Striking consequences of the effect include asymmetric current/field switching of perpendicular magnetization, hysteresis loop shift of perpendicular magnetization in the absence of in-plane direct current, and sharp in-plane magnetic field switching of perpendicular magnetization. Utilizing the intralayer DMI, we demonstrate programable, complete Boolean logic operations within a single spin-orbit torque device. These results will stimulate investigation of the long-range intralayer DMI effect in a variety of spintronic devices.

Dissipative Spin-Wave Diode and Nonreciprocal Magnonic Amplifier

We propose an experimentally feasible dissipative spin-wave diode comprising two magnetic layers coupled via a nonmagnetic spacer. We theoretically demonstrate that the spacer mediates not only coherent interactions but also dissipative coupling. Interestingly, an appropriately engineered dissipation engenders a nonreciprocal device response, facilitating the realization of a spin-wave diode. This diode permits wave propagation in one direction alone, given that the coherent Dzyaloshinskii-Moriya (DM) interaction is balanced with the dissipative coupling. The polarity of the diode is determined by the sign of the DM interaction. Furthermore, we show that when the magnetic layers undergo incoherent pumping, the device operates as a unidirectional spin-wave amplifier. The amplifier gain is augmented by cascading multiple magnetic bilayers. By extending our model to a one-dimensional ring structure, we establish a connection between the physics of spin-wave amplification and non-Hermitian topology. Our proposal opens up a new avenue for harnessing inherent dissipation in spintronic applications.

Tailoring Interlayer Chiral Exchange by Azimuthal Symmetry Engineering

Recent theoretical and experimental studies of the interlayer Dzyaloshinskii-Moriya interaction (DMI) have sparked great interest in its implementation into practical magnetic random-access memory (MRAM) devices, due to its capability to mediate long-range chiral spin textures. So far, experimental reports focused on the observation of interlayer DMI, leaving the development of strategies to control interlayer DMI's magnitude unaddressed. Here, we introduce an azimuthal symmetry engineering protocol capable of additive/subtractive tuning of interlayer DMI through the control of wedge deposition of separate layers and demonstrate its capability to mediate field-free spin-orbit torque (SOT) magnetization switching in both orthogonally magnetized and synthetic antiferromagnetically coupled systems. Furthermore, we showcase that the spatial inhomogeneity brought about by wedge deposition can be suppressed by specific azimuthal engineering design, ideal for practical implementation. Our findings provide guidelines for effective manipulations of interlayer DMI strength, beneficial for the future design of SOT-MRAM or other spintronic devices utilizing interlayer DMI.