X-ray imaging of the dynamic magnetic vortex core deformation

Magnetic platelets with a vortex configuration are attracting considerable attention. The discovery that excitation with small in-plane magnetic fields or spin polarised currents can switch the polarisation of the vortex core did not only open the possibility of using such systems in magnetic memories, but also initiated the fundamental investigation of the core switching mechanism itself. Micromagnetic models predict that the switching is mediated by a vortex-antivortex pair, nucleated in a dynamically induced vortex core deformation. In the same theoretical framework, a critical core velocity is predicted, above which switching occurs. Although these models are extensively studied and generally accepted, experimental support has been lacking until now. In this work, we have used high-resolution time-resolved X-ray microscopy to study the detailed dynamics in vortex structures. We could reveal the dynamic vortex core deformation preceding the core switching. Also, the threshold velocity could be measured, giving quantitative comparison with micromagnetic models

Energy localization in pumped systems

Considering a local nonlinear oscillator interacting with a chain of coupled Linear oscillators, we demonstrate that the dynamics of the local oscillator is characterized by a frequency-dependent damping constant, related to the frequency-dependent density of states of the linear modes. Further, we demonstrate how this intrinsic damping provides possibilities for multiple steady states of the nonlinear oscillator, and how these steady states may create local potentials for electrons that are adiabatically coupled with the linear modes. Finally, the implications on coarse-grained mode-ling of hard, softy and biological matter are discussed

Langevin dynamics of conformational transformations induced by the charge–curvature interaction

The role of thermal fluctuations in the conformational dynamics of a single closed filament is studied. It is shown that, due to the interaction between charges and bending degrees of freedom, initially circular chains may undergo transformation to polygonal shape