Bistability of vortex core dynamics in a single perpendicularly magnetized nanodisk.

Microwave spectroscopy of individual vortex-state magnetic nanodisks in a perpendicular bias magnetic field H is performed using a magnetic resonance force microscope. It reveals the splitting induced by H on the gyrotropic frequency of the vortex core rotation related to the existence of the two stable polarities of the core. This splitting enables spectroscopic detection of the core polarity. The bistability extends up to a large negative (antiparallel to the core) value of the bias magnetic field Hr, at which the core polarity is reversed. The difference between the frequencies of the two stable rotational modes corresponding to each core polarity is proportional to H and to the ratio of the disk thickness to its radius. Simple analytic theory in combination with micromagnetic simulations give a quantitative description of the observed bistable dynamics.

Magnetic resonance studies of the fundamental spin-wave modes in individual submicron Cu/NiFe/Cu perpendicularly magnetized disks.

Spin-wave spectra of perpendicularly magnetized disks consisting of a 100 nm permalloy layer sandwiched between two Cu layers of 30 nm are measured individually by a magnetic resonance force microscope. Using 3D micromagnetic simulations, it is demonstrated that, for submicron-size diameters, the lowest energy spin-wave mode of the saturated state is not spatially uniform, but rather is localized at the center of the Py/Cu interfaces in the region of the minimum demagnetizing field.

Scanning secondary ion analytical microscopy with parallel detection.

The secondary ion microscope described here allows to obtain the simultaneous registration of chemical and isotopic distribution maps of several elements composing the sample. The instrument has been specially designed to optimize both sensitivity and selectivity; bombardment with primary Cs+ ions to increase the ionization yields of negative secondary ions, efficient collection of secondary ions at the target surface, matching of the secondary ion beam etendue with the acceptance of the mass spectrometer working at high mass resolution, spectrometer with parallel detection capabilities. The probe diameter can be made as low as 30 nm and ion induced electron images registered at the same time as ion images. Presently, four ion micrographs are obtained simultaneously over a field of view up to 20 x 20 micro m2 containing up to 512 x 512 pixels. Examples are shown with an ion probe diameter of 0.1 microm.