The interesting physics and potential memory technologies resulting from topologically protected spin textures such as skyrmions, has prompted efforts to discover new material systems that can host these kind of magnetic structures. Here we use the highly tunable magnetic properties of amorphous Fe/Gd multilayer films to explore the magnetic properties that lead to dipole-stabilized skyrmions and skyrmion lattices that form from the competition of dipolar field and exchange energy. Using both real space imaging and reciprocal space scattering techniques we determined the range of material properties and magnetic fields where skyrmions form.Micromagnetic modeling closely matches our observation of small skyrmion features (~50 to 70nm) and suggests these class of skyrmions have a rich domain structure that is Bloch like in the center of the film and more Néel like towards each surface. Our results provide a pathway to engineer the formation and controllability of dipole skyrmion phases in a thin film geometry at different temperatures and magnetic fields.

The dynamic response of dipole skyrmions in Fe/Gd multilayer films is investigated by ferromagnetic resonance measurements and compared to micromagnetic simulations. We detail thickness and temperature dependent studies of the observed modes as well as the effects of magnetic field history on the resonant spectra. Correlation between the modes and the magnetic phase maps constructed from real-space imaging and scattering patterns allows us to conclude the resonant modes arise from local topological features such as dipole skyrmions but does not depend on the collective response of a closed packed lattice of these chiral textures. Using, micromagnetic modeling, we are able to quantitatively reproduce our experimental observations which suggests the existence of localized spin-wave modes that are dependent on the helicity of the dipole skyrmion. We identify four localized spin wave excitations for the skyrmions that are excited under either in-plane or out-of-plane r.f. fields. Lastly we show that dipole skyrmions and non-chiral bubble domains exhibit qualitatively different localized spin wave modes.

Recently, Lorentz transmission electron microscopy (LTEM) has helped researchers advance the emerging field of magnetic skyrmions. These magnetic quasi-particles, composed of topologically non-trivial magnetization textures, have a large potential for application as information carriers in low-power memory and logic devices. LTEM is one of a very few techniques for direct, real-space imaging of magnetic features at the nanoscale. For Fresnel-contrast LTEM, the transport of intensity equation (TIE) is the tool of choice for quantitative reconstruction of the local magnetic induction through the sample thickness. Typically, this analysis requires collection of at least three images. Here, we show that for uniform, thin, magnetic films, which includes many skyrmionic samples, the magnetic induction can be quantitatively determined from a single defocused image using a simplified TIE approach.

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increased, the lasing spectrum is shifted from short to long wavelength with SMSR (Side mode suppression ratio) larger than 20 dB. The tuning range is measured to be about 40 nm with a maximum current of 42 mA. CONCLUSIONA hybrid-integrated tunable source, which is composed of an R-SOA and a polymer double-ring-resonator followed by a loopback mirror is proposed. The wavelength-selective reflector is fabricated with polymer materials of high-index contrast between core and cladding to allow the ring radius close to 100 lm. The radii of two rings are different from each other, that is, 150 and 156 lm, respectively, to introduce a vernier effect for wide tuning range. The output power is measured to be about 0.75 mW at the driving current of 150 mA. The tuning range is measured to be about 40 nm with a maximum tuning current level of 42 mA. The SMSR is maintained to be larger than 20 dB during tuning. The output power and the SMSR are expected to be greatly improved if the coupling efficiency between the R-SOA and the wavelength-selective reflector is properly optimized and the length of the reflector is adjusted as short as possible through a careful mask design, allowing the tunable source to be used especially for a low-cost WDM-PON optical source.ABSTRACT: A size-independent rectangular resonator supporting a mode with a uniform electromagnetic field is presented. This resonator uses a 2D array of metallic wires emulating an effective medium with zero permittivity at the resonance frequency. The field expressions for the resonator are derived and simulation results are presented and discussed.The proposed size-independent zeroth order electric plasmonic cavity resonator is depicted in Figure 1. The resonator is comprised of nine dielectric (nonmagnetic) regions. The center