Micromagnetic view on ultrafast magnon generation by femtosecond spin current pulses

In this Article we discuss a micromagnetic modelling approach to describe the ultrafast spin-transfer torque excitation of coherent and incoherent magnons on the nanoscale. Implementing the action of a femtosecond spin current pulse entering an orthogonally magnetized thin ferromagnetic film, we reproduce recent experimental results and reveal the factors responsible for the unequal excitation efficiency of various spin waves. Our findings are in an excellent agreement with the results of an analytical description of spin-wave excitation based on classical kinetic equations. Furthermore, we suggest an experimental design allowing for the excitation of laterally propagating spin waves beyond the optical diffraction limit. Our findings demonstrate that the classical micromagnetic picture retains its predictive and interpretative power on femtosecond temporal and nanometer spatial scales

Nanoscale mapping of ultrafast magnetization dynamics with femtosecond Lorentz microscopy

Novel time-resolved imaging techniques for the investigation of ultrafast nanoscale magnetization dynamics are indispensable for further developments in light-controlled magnetism. Here, we introduce femtosecond Lorentz microscopy, achieving a spatial resolution below 100 nm and a temporal resolution of 700 fs, which gives access to the transiently excited state of the spin system on femtosecond timescales and its subsequent relaxation dynamics. We demonstrate the capabilities of this technique by spatio-temporally mapping the light-induced demagnetization of a single magnetic vortex structure and quantitatively extracting the evolution of the magnetization field after optical excitation. Tunable electron imaging conditions allow for an optimization of spatial resolution or field sensitivity, enabling future investigations of ultrafast internal dynamics of magnetic topological defects on 10-nanometer length scales

Anomalous Nernst effect and three-dimensional temperature gradients in magnetic tunnel junctions

Understanding nanoscale temperature gradients in magnetic materials and how it affects their properties can help widen their potential applications. The authors analyze the anomalous Nernst effect in magnetic tunnel junctions and report how temperature gradients influence the thermomagnetic properties in three dimensions

Synchronization and chaotic dynamics of coupled mechanical metronomes

Synchronization scenarios of coupled mechanical metronomes are studied by means of numerical simulations showing the onset of synchronization for two, three, and 100 globally coupled metronomes in terms of Arnol'd tongues in parameter space and a Kuramoto transition as a function of coupling strength. Furthermore, we study the dynamics of metronomes where overturning is possible. In this case hyperchaotic dynamics associated with some diffusion process in configuration space is observed, indicating the potential complexity of metronome dynamics. c 2009 American Institute of Physics. [doi: 10.1063/1.3266924

Numerical calculation of laser-induced thermal diffusion and elastic dynamics

n this article we discuss the implementation of a finite-difference time-domain simulation method, which describes thermal diffusion and elastic dynamics induced by an ultrashort laser-pulse. Besides the pseudocode, we provide an example in which numerical results are compared with experimental data, showing excellent agreement

Long-range order on the atomic scale induced at CoFeB/MgO interfaces

Eilers G, Ulrichs H, Muenzenberg M, Thomas A, Thiel K, Seibt M. Long-range order on the atomic scale induced at CoFeB/MgO interfaces. JOURNAL OF APPLIED PHYSICS. 2009;105(7):073701.The amorphous (a-) CoFeB/crystalline (c-) MgO based tunneling system interface has been studied by means of quantitative high resolution transmission electron microscopy from atomic to micrometer length scales with increasing annealing temperatures. On the micron scale an irregular nucleation is found. On the atomic scale a long-range order is induced by the MgO interface, explaining the high tunnel magnetoresistance values > 100% even for not fully crystallized CoFeB/MgO/CoFeB tunnel junctions. (C) 2009 American Institute of Physics. [DOI:10.1063/1.3100044