P. Pirro

Spin-wave propagation in a microstructured magnonic crystal

Transmission of microwave spin waves through a microstructured magnonic crystal in the form of a Permalloy waveguide of a periodically varying width was studied experimentally and theoretically. The spin wave characteristics were measured by spatially resolved Brillouin light scattering microscopy. A rejection frequency band was clearly observed. The band gap frequency was controlled by the applied magnetic field. The measured spin-wave intensity as a function of frequency and propagation distance is in good agreement with a model calculation.

Design of a spin-wave majority gate employing mode selection

The design of a microstructured, fully functional spin-wave majority gate is presented and studied using micromagnetic simulations. This all-magnon logic gate consists of three-input waveguides, a spin-wave combiner and an output waveguide. In order to ensure the functionality of the device, the output waveguide is designed to perform spin-wave mode selection. We demonstrate that the gate evaluates the majority of the input signals coded into the spin-wave phase. Moreover, the all-magnon data processing device is used to perform logic AND-, OR-, NAND- and NOR- operations.

Spin-wave excitation and propagation in microstructured waveguides of yttrium iron garnet/Pt bilayers

We present an experimental study of spin-wave excitation and propagation in microstructured waveguides consisting of a 100 nm thick yttrium iron garnet/platinum (Pt) bilayer. The life time of the spin waves is found to be more than an order of magnitude higher than in comparably sized metallic structures, despite the fact that the Pt capping enhances the Gilbert damping. Utilizing microfocus Brillouin light scattering spectroscopy, we reveal the spin-wave mode structure for different excitation frequencies. An exponential spin-wave amplitude decay length of 31 μm is observed which is a significant step towards low damping, insulator based micro-magnonics.

Low-damping spin-wave propagation in a micro-structured Co2Mn0.6Fe0.4Si Heusler waveguide

We report on the investigation of spin-wave propagation in a micro-structured Co2Mn0.6Fe0.4Si (CMFS) Heusler waveguide. The reduced magnetic losses of this compound compared to the commonly used Ni81Fe19 allow for the observation of spin-wave propagation over distances as high as 75 μm via Brillouin light scattering (BLS) microscopy. In the linear regime, a maximum decay length of 16.7 μm of the spin-wave amplitude was found. The coherence length of the observed spin-wave modes was estimated to be at least 16 μm via phase-resolved BLS techniques.

All-optical detection of phase fronts of propagating spin waves in a Ni81Fe19 microstripe

We present the determination of the wavelength and phase of propagating spin waves in magnetic microstructures made of Ni81Fe19 using the shorted end of a coplanar waveguide for local excitation. The spin wave characteristics have been measured by phase resolved Brillouin light scattering microscopy. This recently developed technique allows for the unambiguous experimental visualization of the phase structure of propagating spin waves and is employed here to magnetic microstructures. The results show an excellent agreement with the theoretically predicted spin-wave dispersion relations.

Spin-wave logic devices based on isotropic forward volume magnetostatic waves

We propose the utilization of isotropic forward volume magnetostatic spin waves in modern wave-based logic devices and suggest a concrete design for a spin-wave majority gate operating with these waves. We demonstrate by numerical simulations that the proposed out-of-plane magnetized majority gate overcomes the limitations of anisotropic in-plane magnetized majority gates due to the high spin-wave transmission through the gate, which enables a reduced energy consumption of these devices. Moreover, the functionality of the out-of-plane majority gate is increased due to the lack of parasitic generation of short-wavelength exchange spin waves.

A micro-structured ion-implanted magnonic crystal

We investigate spin-wave propagation in a microstructured magnonic-crystal waveguide fabricated by localized ion implantation. The irradiation caused a periodic variation in the saturation magnetization along the waveguide. As a consequence, the spin-wave transmission spectrum exhibits a set of frequency bands, where spin-wave propagation is suppressed. A weak modification of the saturation magnetization by 7% is sufficient to decrease the spin-wave transmission in the band gaps by a factor of 10. These results evidence the applicability of localized ion implantation for the fabrication of efficient micron- and nano-sized magnonic crystals for magnon spintronic applications.

Interference of coherent spin waves in micron-sized ferromagnetic waveguides

We present experimental observations of the interference of spin-wave modes propagating in opposite directions in micron-sized Ni81Fe19-waveguides. To monitor the local spin-wave intensity distribution and phase of the formed interference pattern, we use Brillouin light scattering microscopy. The two-dimensional spin-wave intensity map can be understood by considering the interference of several waveguide eigenmodes with different wavevectors quantized across the width of the stripe. The phase shows a transition from linear dependence on the space coordinate near the antennas characteristic for propagating waves to discrete values in the center region characteristic for standing waves.

Nonlinear emission of spin-wave caustics from an edge mode of a microstructured Co2Mn(0:6)Fe(0:4)Si waveguide.

Magnetic Heusler materials with very low Gilbert damping are expected to show novel magnonic transport phenomena. We report nonlinear generation of higher harmonics leading to the emission of caustic spin-wave beams in a low-damping microstructured Co(2)Mn(0.6)Fe(0.4)Si Heusler waveguide. The source for the higher harmonic generation is a localized edge mode formed by the strongly inhomogeneous field distribution at the edges of the spin-wave waveguide. The radiation characteristics of the propagating caustic waves observed at twice and three times the excitation frequency are described by an analytical calculation based on the anisotropic dispersion of spin waves in a magnetic thin film.

Mode conversion by symmetry breaking of propagating spin waves

We study spin-wave transport in a microstructured Ni81Fe19 waveguide exhibiting broken translational symmetry. We observe the conversion of a beam profile composed of symmetric spin-wave width modes with odd numbers of antinodes n = 1, 3,… into a mixed set of symmetric and asymmetric modes. Due to the spatial homogeneity of the exciting field along the used microstrip antenna, quantized spin-wave modes with an even number n of antinodes across the stripe’s width cannot be directly excited. We show that a break in translational symmetry may result in a partial conversion of even spin-wave waveguide modes.