We present experimental and theoretical investigations of spin wave modes in Permalloy (Ni80Fe20) macrospin arrays in cross and square configurations to understand the dynamics among clusters of them. These configurations are periodically patterned at the central signal line of a coplanar waveguide to acquire strong coupling with the microwave field. Their dynamic behavior is analyzed using broadband ferromagnetic resonance (FMR) measurements. Our results reveal a notable mode-splitting associated with a rotation of the macrospin configuration, highlighting the influence of the geometry on spin wave excitations. Furthermore, the spectra depend on the macrospin configuration as evidenced by the discontinuity of the FMR curves associated with different magnetization reversal fields, and the interaction between modes at low frequency. Theoretical calculations support the experimental observations of fundamental modes and mode-splitting at the vertex region. These findings contribute to the development of artificial spin ice (ASI) for functional magnonic networks and spin-based computing applications.

Materials with low damping, such as Yttrium Iron Garnet (YIG), are of interest in connection with spintronic devices. A promising structure for information storage is the Skyrmion, a domain wall quasi-particle. It has been shown that the stabilization of a Skyrmion can be energetically favorable with the addition of spin–orbit coupling (SOC) through the Dzyaloshinskii–Moriya Interaction (DMI). This interaction should be largest in metals, but still present in insulators. To produce spintronic devices using YIG, we must evaluate the DMI interaction inherent in the substrate used to grow the YIG, which is generally Gadolinium Gallium Garnet (GGG). In this paper, we measure nonreciprocal spin-wave propagation in a thick YIG film to place a limit on the DMI parameter in a YIG/GGG bilayer.

We report experimental and theoretical studies of spin dynamics in lattice structures of permalloy (Ni80Fe20) nano-ellipses, with four different types of networks including honeycomb and square lattices. The lattices are patterned at the center line of the co-planar wave guide and consist of non-contacting or contacting ellipses. Micromagnetic simulations show excellent agreement with the broadband ferromagnetic resonance (FMR) experimental results. We find the existence of a spin-wave mode localized in the vertex region of the contacting nano-ellipse network. Our finding has important implications when designing an artificial spin ice (ASI) network for functional magnonics.

We report broadband ferromagnetic resonance measurements of the in-plane magnetic field response of three- and four-fold symmetric vertices formed by non-contacting permalloy nano-ellipses together with extended lattices constructed from them. Complementing the experimental data with simulations, we are able to show that, as far as the most intense FMR responses are concerned, the spectra of vertices and lattices can largely be interpreted in terms of a superposition of the underlying hysteretic responses of the individual ellipses, as elemental building blocks of the system. This property suggest that it is possible to understand the orientation of the individual magnetic dipole moments in a dipole network in terms of dynamic measurements alone, thereby offering a powerful tool to analyze the alignment statistics in frustrated systems that are exposed to various magnetic histories.

Using parametric excitation, we have studied the minimum frequency associated with the backward volume (BV) spin wave branch in a thin film of the ferrimagnetic material yttrium iron garnet (YIG) for the magnetic field lying in plane and parallel to the wave vector as well as for out-of-plane field angles. We find that there is a drastic change in the efficiency of parametric excitation between two different pumping frequency regimes.

We report the experimental and theoretical characterization of the angular-dependent spin dynamics in arrays of ferromagnetic nanodisks arranged on a honeycomb lattice. The magnetic field and microwave frequency dependence, measured by broadband ferromagnetic resonance, reveal a rich spectrum of modes that is strongly affected by the microstate of the network. Based on symmetry arguments with respect to the external field, we show that certain parts of the ferromagnetic network contribute to the detected signal. A comparison of the experimental data with micromagnetic simulations reveals that different subsections of the lattice predominantly contribute to the high-frequency response of the array. This is confirmed by optical characterizations using microfocused Brillouin light scattering. Furthermore, we find indications that nucleation and annihilation of vortex-like magnetization configurations in the low-field range affect the dynamics, which is different from clusters of ferromagnetic nanoellipses. Our work opens up new perspectives for designing magnonic devices that combine geometric frustration in gyrotropic vortex crystals at low frequencies with magnonic crystals at high frequencies.

We present experimental and theoretical studies of spin-wave mode dynamics in artificial kagome spin ice vertices made of three identical 15-nm thick elongated Ni80Fe20 nanoislands (macrospins). We consider several possible configurations, from completely disjointed macrospins (full dipolar interelement interac-tions) to fully jointed macrospins (full dipolar-exchange interactions). Using angular-resolved magnetic field dependent broadband ferromagnetic resonance (FMR), we demonstrate the occurrence of a mode localized in the vertex region as indicated by the distinct behavior of the FMR spectra at different angles and configurations. Theoretical calculations using micromagnetic simulations support the existence, ori-gin, and behavior of this mode by interpreting it as a localized, quasi-uniform Kittel mode. Our findings pave the way for designing the most appropriate network consisting of ferromagnetic nanomagnets for specific application purposes in magnonics.

Spinwave propagation in yttrium iron garnet (YIG) films has a long history [1] but has recently [...]

Using a multielement antenna, we have performed measurements of the angular dependence of propagating magnetostatic spin waves in a thin yttrium iron garnet film, both in-plane and out-of-plane, and compared the measurements with existing theoretical models. For most magnetic field directions, theory and experiments agree reasonably well. However, there is a range of magnetic field directions where differences between theory and experiment become large.

We report experiments which characterize spin wave propagation in a thin (111) yttrium iron garnet film for arbitrary angles between the in-plane magnetic field and the mode wavevectors. By measuring the magnetic field evolution of the phase of the wave traveling across the film, we deduce the frequency dependence of the wavevector, the dispersion relation, from which the mode velocity follows. Additionally, we observe multiple nodes in the regime of the propagating Damon-Eshbach mode; these arise from avoided crossings associated with the higher, exchange split, standing wave modes along the film normal, the positions of which correlate with the direct absorption measurements of their positions. This information allows a determination of the exchange parameter. Using this technique, we examine the nonreciprocity in spin wave propagation that results from an adjacent metal layer.

We report the properties of superconductivity and Hall effect in 100 nm Pb[Formula: see text]Bi[Formula: see text] alloy thin films which were prepared by thermal evaporation with quench condensation using liquid nitrogen. X-ray diffraction indicates the films are [Formula: see text]-phase with peaks shifted to lower angles compared to pure Pb. The [Formula: see text] of the films was higher than those of an amorphous Pb–Bi alloy thin film of the same composition and pure bulk Pb. The resistivity, critical field and critical current density of the thin films are reported. The coherence length ([Formula: see text][Formula: see text]) and London penetration depth ([Formula: see text]) near [Formula: see text] were calculated from the experimental results. The films are in the dirty limit and behave as type-II superconductors with a Ginzburg–Landau parameter of about 10. Additionally, the films show sign reversal in Hall measurements. These films have been quite useful in a comprehensive study of the effects of flux pinning by integrated ferromagnetic nanostructures conducted in hybrid ferromagnet–superconductor samples in our lab over the past few years due to their single-phase nature and strong type-II behavior.

We demonstrate that micrometer-scale spin waves can be excited in a thin film of the ferrimagnetic material yttrium iron garnet (YIG) using patterned, multi-element antennas. The magnitude of the dynamic magnetic field generated by such antennas decays exponentially along the thickness direction, and this leads to an enhanced coupling to modes having a surface-like character as opposed to a more sinusoidal bulk-like character. We have used this property to identify spin waves having a mixed bulk/surface character.

We experimentally and theoretically characterize the angular-dependent microwave response of three-macrospin-vertex structures that can serve as a node in various spin ice lattices. The macrospins consist of patterned permalloy thin films with an elliptical cross section together with an in-plane aspect ratio allowing an Ising-like behavior together with bulk modes as low-frequency excitations in the field range of interest. Various branches of the frequency-magnetic field curves display atypical behaviors and discontinuities, together with softening due to macrospin reversals. The overall behavior observed accurately corresponds to a superposition of the spectra of the individual macrospins. The measured ferromagnetic resonance spectra are in good agreement with theoretical modeling. In particular, they reveal a close correlation between the field direction (relative to the individual macrospins), and the corresponding frequency-magnetic field curve, i.e., between the geometry and the magnetic response.

We characterize thermally quench condensed (similar to 80 K) Sn thin films of two different thicknesses to explore their usefulness for vortex studies. The coherence length and the London penetration depth near the critical temperature indicate that the thin films are in the dirty limit and behave as type II superconductors. Furthermore, when we add ferromagnetic nanostripes on top of the Sn thin films, the ferromagnet-superconductor hybrids show hysteric and anisotropic behavior. A ferromagnet-superconductor hybrid with a thinner Sn film exhibits a stronger effect.

We report the experimental and theoretical characterization of the angular dependent magnetic field and microwave frequency response of isolated mesoscopic permalloy nanoellipses for geometries in which the static magnetic field is either parallel or perpendicular to the microwave magnetic field. We show how these spectra form a basis for interpreting the ferromagnetic resonance spectra of lattices based on such structures, including those containing frustrated regions, such as artificial spin ice structures.

We report systematic measurements of the dispersion of long wavelength spin waves for a wide range of wave vectors for the magnetic field along the three principal directions defining the forward volume, backward volume and Damon-Eshbach modes of a 9.72 μm thick film of an yttrium iron garnet obtained using lithographically patterned, multi-element, spatially resonant, antennas. Overall good agreement is found between the experimental data for the backward volume and Damon-Eshbach modes and the magnetostatic theory of Damon and Eshbach. Also, good agreement is found between the experimental data for the forward volume mode and the theory of Damon and van de Vaart.

We have observed the propagation of spin waves across a thin yttrium iron garnet film on (111) gadolinium gallium garnet for magnetic fields inclined with respect to the film plane. Two principle planes were studied: that for H in the plane defined by the wave vector k and the plane normal, n, with limiting forms corresponding to the Backward Volume and Forward Volume modes, and that for H in the plane perpendicular to k, with limiting forms corresponding to the Damon-Eshbach and Forward Volume modes. By exciting the wave at one edge of the film and observing the field dependence of the phase of the received signal at the opposing edge we determined the frequency vs. wavevector relation, omega = omega (k), of various propagating modes in the film. Avoided crossings are observed in the Damon-Eshbach and Forward Volume regimes when the propagating mode intersects the higher, exchange split, volume modes, leading to an extinction of the propagating mode; analysis of the resulting behavior allows a determination of the exchange parameter. The experimental results are compared with theoretical simulations. (C) 2018 Elsevier B.V. All rights reserved.

We experimentally investigate and model the effects of a copper surface adjacent to a surface on which spin waves propagate in a thin film of yttrium iron garnet (YIG). Investigation was performed using a phase detection method, which can map out the spin wave velocity as a function wavevector for small wavevector with high resolution. This velocity is in good agreement with a simple model and allows for extraction of the separation between the YIG film and the copper.