Volume 95, Issue 7, 01 April 2004
Index of content:
- MAGNETISM AND SUPERCONDUCTIVITY (PACS 74-76)
95(2004); http://dx.doi.org/10.1063/1.1650889View Description Hide Description
We introduce the concept of computerized tomographic microscopy in magnetic resonance imaging using the magnetic fields and field gradients from a ferromagnetic probe. We investigate a configuration where a two-dimensional sample is under the influence of a large static polarizing field, a small perpendicular radio-frequency field, and a magnetic field from a ferromagnetic sphere. We demonstrate that, despite the nonuniform and nonlinear nature of the fields from a microscopic magnetic sphere, the concepts of computerized tomography can be applied to obtain proper image reconstruction from the original spectral data by sequentially varying the relative sample-sphere angular orientation. The analysis shows that the recent proposal for atomic resolution magnetic resonance imaging of discrete periodic crystal lattice planes using ferromagnetic probes can also be extended to two-dimensional imaging of noncrystalline samples with resolution ranging from micrometer to angstrom scales.
95(2004); http://dx.doi.org/10.1063/1.1655679View Description Hide Description
The temperature-dependent Hall resistivity and carrier concentrations of epilayers grown on (100) semi-insulating GaAs substrates by molecular beam epitaxy have been investigated in the temperature range of 10–300 K. A sample with shows typical insulator behavior and samples with and 3.7 % show typical metallic behavior. A model taking into account ionized impurity and spin disorder scattering mechanisms was used to portray properly the observed features of the temperature-dependent Hall resistivity data. The value of the exchange energy was and 71.9±0.5 eV Å3 for the samples with and 3.7 %, respectively. Ionized impurity scattering dominates the entire temperature range, with a temperature-independent spin disorder scattering in the paramagnetic region. It was found that the spin disorder scattering mechanism had a strong temperature dependence on in the ferromagnetic region.
95(2004); http://dx.doi.org/10.1063/1.1667597View Description Hide Description
Elliptical (track-shaped) permalloy dots, in which magnetic circular vortex and antivortex structures are stabilized, were prepared and the magnetic properties of perpendicular magnetization spots (turned-up magnetizations) at the cores of both types of vortices were studied. Using magnetic force microscopy, the direction of the turned-up magnetization was detected and the switching field was measured. It was found that the value of the switching field of the turned-up magnetization at the antivortex core is smaller by about 1000 Oe than that at the circular vortex core. It was confirmed that the switching of the turned-up magnetization in the antivortex is not influenced by the directions of the turned-up magnetizations in the neighboring circular vortices. Vanishing and regenerating processes of turned-up magnetizations were observed by increasing and decreasing the magnetic field applied to the in-plane direction.