Dual dielectric relaxation of the permittivity and multiple magnetic resonances of the permeability (including one natural resonance and two exchange resonance modes) are observed in CoNi@C nanocapsules in the same 5–17 GHz frequency range which leads to a better electromagnetic-wave absorption than earlier reported for nanocomposites. A reflection loss (RL) exceeding −25 dB is obtained in a wide frequency range of 5–17 GHz when an appropriate absorber thickness between 2 and 4.8 mm is chosen. For a 2 mm absorber layer, a RL value exceeding −10 dB is achieved in the broad frequency range 12–18 GHz, which covers the whole Ku-band.

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We show by micromagnetic simulations that spontaneous skyrmion ground state can exist in Co/Ru/Co nanodisks without the Dzyaloshinsky-Moriya interaction (DMI), which can remain stable in the applied magnetic field along +z direction even up to 0.44 T. The guiding center (Rx,Ry) of skyrmion defined by the moments of the topological density presents a novel gyration with a star-like trajectory in a pulsed magnetic field and a hexagonal trajectory after the field is switched off, which is different from that of vortex or bubble. One of the coupled skyrmions could move without an external magnetic field, but only induced by the motion of the other one due to strong inter-layer magnetostatic interactions. This work sheds light on how novel skyrmions can be discovered in various (not limited to magnetic) systems with competing energies and contributes to the understanding of the dynamical properties of skyrmion.