Stroboscopic Technique for Dynamic Observation of Ferromagnetic Domains at Low Frequencies in Scanning Electron Microscopy

A new stroboscopic technique for the observation of periodic phenomena at low frequencies (10 -100 Hz) in scanning electron microscopy (SEM) is developed in the present study. This new technique is based on the line-sampling stroboscopy instead of the point-sampling stroboscopy which has been commonly used for the dynamic observation at high frequencies (\u3e 1 kHz). In this stroboscopy, a multi-frame display with the individual stroboscopic image at different phase can be easily introduced with no reduction of the detection efficiency. The main application of the present stroboscopy at low frequencies is the dynamic observation of magnetic domains. In this case, high voltage scanning electron microscopy is very effective to increase the magnetic contrast as pointed out by several workers. According to this, dynamic observation of Fe-Si 3% single crystals under a drive field of line frequency (60 Hz) using a 200 kV high voltage SEM (JSEM-200, JEOL Co. Ltd.) is achieved in this paper, as a typical application of this new stroboscopy. From these dynamic observation, it is concluded that this new technique is a very useful tool to analyze the dynamic property of magnetic materials in practical use

In-situ growth of superconducting NdFeAs(O,F) thin films by Molecular Beam Epitaxy

The recently discovered high temperature superconductor F-doped LaFeAsO and related compounds represent a new class of superconductors with the highest transition temperature (Tc) apart from the cuprates. The studies ongoing worldwide are revealing that these Fe-based superconductors are forming a unique class of materials that are interesting from the viewpoint of applications. To exploit the high potential of the Fe-based superconductors for device applications, it is indispensable to establish a process that enables the growth of high quality thin films. Efforts of thin film preparation started soon after the discovery of Fe-based superconductors, but none of the earlier attempts had succeeded in an in-situ growth of a superconducting film of LnFeAs(O,F) (Ln=lanthanide), which exhibits the highest Tc to date among the Fe-based superconductors. Here, we report on the successful growth of NdFeAs(O,F) thin films on GaAs substrates, which showed well-defined superconducting transitions up to 48 K without the need of an ex-situ heat treatment

Formation of Deeply Bound Kaonic Atoms in (K^-,N) Reactions

We study theoretically the (K^-,N) reactions for the formation of the deeply bound kaonic atoms, which were predicted to be quasi--stable with narrow widths, using the Green function method. We consider various cases with different target nuclei and energies systematically and find the clear signals in the theoretical spectra for all cases considered in this article. The signals show very interesting structures, such as the $RESONANCE DIP$ instead of the resonance peak. We discuss the origins of the interesting structures and possibilities to get new information on the existence of the kaonic nuclei from the spectra of the atomic state formations.Comment: 11 pages, 9 figure

Momentum dependence of the energy gap in the superconducting state of optimally doped Bi2(Sr,R)2CuOy (R=La and Eu)

The energy gap of optimally doped Bi2(Sr,R)2CuOy (R=La and Eu) was probed by angle resolved photoemission spectroscopy (ARPES) using a vacuum ultraviolet laser (photon energy 6.994 eV) or He I resonance line (21.218 eV) as photon source. The results show that the gap around the node at sufficiently low temperatures can be well described by a monotonic d-wave gap function for both samples and the gap of the R=La sample is larger reflecting the higher Tc. However, an abrupt deviation from the d-wave gap function and an opposite R dependence for the gap size were observed around the antinode, which represent a clear disentanglement between the antinodal pseudogap and the nodal superconducting gap.Comment: Submitted as the proceedings of LT2