Magnetic skyrmions are topologically non-trivial spin structure, and their existence in ferromagnetically coupled multilayers has been reported with disordered arrangement. In these multilayers, the heavy metal spacing layers provide an interfacial Dzyaloshinskii-Moriya interaction (DMI) for stabilizing skyrmions at the expense of interlayer exchanging coupling (IEC). To meet the functional requirement of ordered/designable arrangement, in this work, we proposed and experimentally demonstrated a scenario of skyrmion nucleation using nanostructured synthetic antiferromagnetic (SAF) multilayers. Instead of relying on DMI, the antiferromagnetic IEC in the SAF multilayers fulfills the role of nucleation and stabilization of skyrmions. The IEC induced skyrmions were identified directly imaged with MFM and confirmed by magnetometry and magnetoresistance measurements as well as micromagnetic simulation. Furthermore, the robustness of the proposed skyrmion nucleation scenario was examined against temperature (from 4.5 to 300 K), device size (from 400 to 1200 nm), and different lattice designs. Hence, our results provide a synthetic skyrmion platform meeting the functional needs in magnonic and spintronic applications.

Magnetic skyrmions are novel topological spin textures on the nanoscale, and significant efforts have been taken to improve their zero-field density at room temperature (RT). In this work, we reported an approach of improving zero-field skyrmion density in [Pt/Co/Fe/Ir] 2 multilayers at RT by using the first-order reversal curve (FORC) technique to obtain information on the irreversible or reversible behaviors in the magnetization switching process. It was found from the FORC diagram that the magnetization reversal mechanism can be characterized into three stages: (1) reversible labyrinth stripe domains expanding or shrinking stage; (2) irreversible stripe domains fracturing stage; and (3) irreversible skyrmion annihilation stage. Furthermore, the zero-field skyrmion density can be highly improved by choosing reversal fields from the irreversible stripe domains fracturing stage. The highest skyrmion density was approached according to the maximum FORC distribution ρ. Our results have established the FORC measurement as a valuable tool for investigating magnetic multilayers of high skyrmion densities.

In recent years, magnon and spin texture are attracting great interest in condensed matter physics and magnetism. Magnonics is aiming to use magnon as information carriers to realize functions for storage, transmission, and processing. Magnetic skyrmion is representative spin texture due to its topologically nontrivial properties. Since skyrmions are topologically protected, their transformation to other spin configurations requires overcoming additional topological energy barriers. Therefore, skyrmions are more stable than other trivial spin textures. In addition, the characters of nanoscale size, quasiparticle properties, and various excitation modes make them a potential candidate for spintronic application. Magnon and skyrmion, as two fundamental excitations, can coexist in magnetic systems and interplay with each other through direct exchange interactions. In this review, we provide an overview of recent theoretical and experimental studies on magnon–skyrmion interactions. We mainly focus on three kinds of magnon–skyrmion interactions: (i) magnon scattering by skyrmion, (ii) skyrmion motion driven by magnon, and (iii) coupling between magnon and skyrmion modes. The first two kinds of interactions could be clearly explained by the wave-particle interaction model on the classical level. Alternatively, the last kind of interaction could be understood by the coupled harmonic oscillator model on the quantum level, which indicates fast energy exchange and hybrid magnon states. The exploration focused on quantum phenomena of magnon has led to the emerging field of quantum magnonics and promoted applications of magnon in quantum information storage and processing. In the end, we give a perspective on the exploration of magnon–skyrmion interaction in quantum magnonics.

A magnetic skyrmion is a promising candidate for information carrier in future logic functional devices, ultra-density storage devices, and neuromorphic computing. The presence of interfacial Dzyaloshinskii–Moriya interaction in magnetron sputtered multilayers results in the spontaneous nucleation of magnetic skyrmion. However, the precise control of position and arrangement of magnetic skyrmion spontaneously nucleated in multilayers is still a significant challenge. Artificial skyrmion, generated by various external stimuli, shows high promise for manipulating the spatially ordered arrangement on demand. In this review, we summarize the progress of artificial skyrmion with various formation mechanisms. After introducing the concept of artificial skyrmion, we will focus on several methods of producing artificial skyrmion in magnetic multilayers using spin texture imprinting, integrated bias magnet, local magnetic field gradient, optical irradiation, and nanolithography. In the end, we give a perspective of the potential applications of artificial skyrmions for cavity magnonics and quantum spintronics.

Synthetic antiferromagnetic (SAF) multilayers are a kind of functional materials with great potential for spintronic devices. Many excellent properties of SAF multilayers have been widely reported in previous works. Here, we experimentally found that the magnetization switching steps n of [Pt/Co]2/Ru/[Co/Pt]4 SAF multilayers with perpendicular magnetic anisotropy are highly dependent on the temperature and magnetic field sweeping rate by magneto-optic Kerr effect and anomalous Hall resistance measurement. It is found that the contribution of the upper and lower layers of the SAF multilayers to the anomalous Hall coefficients is different. The switching steps n change from 2 to 3 by reducing the thickness of the non-magnetic spacer, decreasing the sweeping rate of the magnetic field, and increasing the temperature of the measuring environment. Our findings could provide a method to achieve multi-step magnetization switching for functional spintronic devices.