In situ magnetoresistance measurements of ferromagnetic nanocontacts in the Lorentz transmission electron microscope

We report on in situ magnetoresistance measurements of a 30-nm-wide ferromagnetic nanocontact with simultaneous magnetic imaging in the Lorentz transmission electron microscope. The magnetoresistive measurements are correlated with the micromagnetic configuration of the sample. This allows us to assign characteristic features in the magnetoresistance curves to different magnetic configurations of the sample. From our experiments we can conclude that the micromagnetic configuration of the whole sample—not only the nanocontact region—has to be taken into account for the interpretation of magnetoresistive effects or hysteresis loops. Micromagnetic simulations were performed which confirm the experimental results

Observation of the propagation and interference of spin waves in ferromagnetic thin films

We have observed the propagation of spin waves and spin-wave packets in 20-nm-thick Permalloy films upon microwave excitation by means of time-resolved scanning Kerr microscopy. Spin waves can be detected up to 80 mu m away from the driving coplanar strip line. In doing so, we were able to directly determine the phase velocities, dispersion relations and group velocities for different geometries of an externally applied in-plane magnetic field. In addition, we report on the direct optical observation of spin-wave interference with lateral and time (phase) resolution

Spin-Wave Eigenmodes of Permalloy Squares with a Closure Domain Structure

Quantized spin-wave eigenmodes in single, 16 nm thick and 0.75 to 4 µm wide square permalloy islands with a fourfold closure domain structure have been investigated by microfocus Brillouin light scattering spectroscopy and time resolved scanning magneto-optical Kerr microscopy. Up to six eigenmodes were detected and classified. The main direction of the spin-wave quantization in the domains was found to be perpendicular to the local static magnetization. An additional less pronounced quantization along the direction parallel to the static magnetization was also observed

Mode degeneracy due to vortex core removal in magnetic disks

The mode spectrum of micrometer-sized ferromagnetic Permalloy disks, exhibiting a vortex ground state, is investigated by means of time-resolved scanning Kerr microscopy. The temporal evolution of the magnetization is probed after application of a fast in-plane field pulse. The lowest order azimuthal mode, a mode with only one diametric node, splits into a doublet as the disk diameter decreases. Theoretical models show that this splitting is a consequence of the interaction of the mode with the gyrotropic motion of the vortex core. Our experiments and micromagnetic simulations confirm that by removing the vortex core from the disk, the mode splitting vanishes