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Magnetic skyrmions are topological spin textures that can be used as memory and logic components for advancing the next generation spintronics. In this regard, control of nanoscale skyrmions, including their sizes and densities, is of particular importance for enhancing the storage capacity of skyrmionic devices. Here, we propose a viable route for engineering ferrimagnetic skyrmions via tuning the magnetic properties of the involved ferrimagnets Fe1-xTbx. Via tuning the composition of Fe1-xTbx that alters the magnetic anisotropy and the saturation magnetization, the size of the ferrimagnetic skyrmion (ds) and the average density (ηs) can be effectively tailored in [Pt/Fe1-xTbx/Ta]10 multilayers. In particular, a stabilization of sub-50 nm skyrmions with a high density is demonstrated at room temperature. Our work provides an effective approach for designing ferrimagnetic skyrmions with the desired size and density, which could be useful for enabling high-density ferrimagnetic skyrmionics.

Phase mixture single layer film with 3-dimensional spatial distribution of internal interfaces between ferromagnetic and antiferromagnetic nanoclusters was achieved through the inhomogeneous distribution of oxygen atoms within the ferromagnetic transition metal thin film layer. In the present work, enhanced exchange bias properties of phase mixture single layer film including both exchange and super-exchange couplings within the body of the single layer were investigated under various conditions. The film exhibited same exchange bias field regardless of the layer thickness, which violates the known relationship of inverse proportionality between the exchange bias field and the thickness of the magnetic layer in the conventional ferromagnet/antiferromagnet bilayers systems. Furthermore, it was found that the exchange bias could be set in any direction with respect to the film surface, removing the restriction by the magnetic shape anisotropy of the thin film structure. Low blocking temperature of the phase mixture single layer film could also be overcome with an additional neighboring antiferromagnet layer.

A wide variety of coupled harmonic oscillators exist in nature1. Coupling between different oscillators allows for the possibility of mutual energy transfer between them2-4 and the information-signal propagation5,6. Low-energy input signals and their transport with low-energy dissipation are the key technical factors in the design of information processing devices7. Here, utilizing the concept of coupled oscillators, we experimentally demonstrated a robust new mechanism for energy transfer between spatially separated dipolar-coupled magnetic disks - stimulated vortex gyration. Direct experimental evidence was obtained by time-resolved soft X-ray microscopy. The rate of energy transfer from one disk to the other was deduced from the two normal modes' frequency splitting caused by dipolar interaction. This mechanism provides the advantages of tunable energy transfer rate, low-power input signal, and low-energy dissipation for magnetic elements with negligible damping. Coupled vortex-state disks are promising candidates for information-signal processing devices that operate above room temperature.