We report on the design, verification and performance of MUMAX3, an open-source GPU-accelerated micromagnetic simulation program. This software solves the time- and space dependent magnetization evolution in nano- to micro scale magnets using a finite-difference discretization. Its high performance and low memory requirements allow for large-scale simulations to be performed in limited time and on inexpensive hardware. We verified each part of the software by comparing results to analytical values where available and to micromagnetic standard problems. MUMAX3 also offers specific extensions like MFM image generation, moving simulation window, edge charge removal and material grains

We present an experimental investigation of radial spin-wave modes in magnetic nano-disks with a vortex ground state. The spin-wave amplitude was measured using a frequency-resolved magneto optical network analyzer, allowing for high-resolution resonance curves to be recorded. It was found that with increasing excitation amplitude up to about 10 mT, the lowest-order mode behaves strongly non-linearly as the mode frequency redshifts and the resonance peak strongly deforms. This behavior was quantitatively reproduced by micromagnetic simulations. At higher excitation the spinwaves are transformed into a soliton by self-focusing, and collapse onto the vortex core, dispersing the energy in short-wavelength spinwaves. Additionally, this process can lead to switching of the vortex polarization through the injection of a Bloch point.The study of the static and dynamic properties of micron and sub-micron sized magnetic platelets is not only necessary for the development of new technological applications, but is also interesting for fundamental reasons, as they can be simple model systems to investigate magnetic interactions and the complex dynamics involved. This is especially true for platelets with a magnetic vortex ground state configuration. It is the simplest, non-trivial configuration in a magnet and a building block of more complex states. Such vortex configurations know several modes of excitation. The lowest frequency mode is the gyrotropic mode (typically in the sub-GHz range) 1,2 , and corresponds to cyclic motion of the vortex around the center of the structure. This mode has already been studied extensively, especially because its excitation can lead to switching of the vortex core 3-5 . At higher frequency (typically several GHz), azimuthal modes exist 6,7 . These modes hardly move the vortex core, but the magnetization is excited out-of-plane with a periodicity in function of the azimuthal angle and the wave vector k parallel to the magnetization m. Because of azimuthal symmetry, this mode is divided in clockwise (CW) and counter clockwise (CCW) modes. However, the coupling with the vortex core, lifts the degeneration between these modes and can result in uni-directional switching of the vortex core 8 . The third excitation mode is the radial spin wave mode. Here the out-of-plane excursion amplitude of the magnetization is now a function of the radius. As the wave vector is perpendicular to the magnetization direction, this is a Damon-Eschbach mode. Until now, experimental work has only focused on the low excitation regime where the response is linear 9-12 , but recent numerical studies predict that at higher excitation levels vortex core switching 13,15 and non-linear phenomena can appear 15,16 . Here, we present an experimental investigation of the non-linear regime of the radial spinwave mode and further elaborate on the non-linear phenomena a) Electronic mail: Mathias.Helsen@UGent.be appearing near the core switching threshold.Our samples consisted of 1µm Permalloy discs, 10nm in thickness located in ...

We present a method for the investigation of gigahertz magnetization dynamics of single magnetic nano elements. By combining a frequency domain approach with a micro focus Kerr effect detection, a high sensitivity to magnetization dynamics with submicron spatial resolution is achieved. It allows spectra of single nanostructures to be recorded. Results on the uniform precession in soft magnetic platelets are presented.

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SUMMARYactivation analysis is developed. (Ti12 = 8.04 d) produced can be measured purely instrumentally. When the molybdenum/tellurium ratio exceeds 25, a radiochemical separation is required. The pure l31I activity can then be measured interference-free. The tellurium content of 7 NBS-reference cast irons with concentrations varying from 50 to 750 ppm is measured. The reproducibility is generally better than 6% and the accuracy is good.