Direct observation of the vortex core magnetization and its dynamics

Square-shaped thin film structures with a single magnetic vortex were investigated using a scanning transmission x-ray microscope. The authors report on the direct observation of the vortex core in 500x500 nm(2), 40 nm thick soft magnetic Ni-Fe samples. The static configuration of the vortex core was imaged as well as the gyrotropic motion of the core under excitation with an in-plane alternating magnetic field. This enabled them to directly visualize the direction of the out-of-plane magnetization in the vortex core (up or down). The reversal of the core was effected by short bursts of an alternating magnetic field. An asymmetry appears in the core's trajectory for its orientation pointing up and down, respectively

In situ measurements of angular-dependent light scattering by aerosols over the contiguous United States

This work provides a synopsis of aerosol phase function (F11) and polarized phase function (F12) measurements made by the Polarized Imaging Nephelometer (PI-Neph) during the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and the Deep Convection Clouds and Chemistry (DC3) field campaigns. In order to more easily explore this extensive dataset, an aerosol classification scheme is developed that identifies the different aerosol types measured during the deployments. This scheme makes use of ancillary data that include trace gases, chemical composition, aerodynamic particle size and geographic location, all independent of PI-Neph measurements. The PI-Neph measurements are then grouped according to their ancillary data classifications and the resulting scattering patterns are examined in detail. These results represent the first published airborne measurements of F11 and −F12∕F11 for many common aerosol types. We then explore whether PI-Neph light-scattering measurements alone are sufficient to reconstruct the results of this ancillary data classification algorithm. Principal component analysis (PCA) is used to reduce the dimensionality of the multi-angle PI-Neph scattering data and the individual measurements are examined as a function of ancillary data classification. Clear clustering is observed in the PCA score space, corresponding to the ancillary classification results, suggesting that, indeed, a strong link exists between the angular-scattering measurements and the aerosol type or composition. Two techniques are used to quantify the degree of clustering and it is found that in most cases the results of the ancillary data classification can be predicted from PI-Neph measurements alone with better than 85 % recall. This result both emphasizes the validity of the ancillary data classification as well as the PI-Neph's ability to distinguish common aerosol types without additional information

Magnetic behaviour of layered Ag(II) fluorides

Magnetic behaviour of layered Ag(II) fluorides.</p

Vortex dynamics in Permalloy disks with artificial defects: Suppression of the gyrotropic mode

The dynamics of magnetic vortices in thin Permalloy disks having artificial defects in the form of small holes at different locations within the disk has been investigated by means of frequency-domain spatially resolved ferromagnetic resonance. It is found that the vortex can be effectively captured by such a defect. Consequently the commonly observed gyrotropic vortex motion in an applied microwave field of 1 mT is suppressed. However, if in addition a static magnetic field of at least 4.3 mT is applied, the vortex core is nucleated from the artificial defect and a modified gyrotropic motion starts again. (c) 2007 American Institute of Physics