Flux Line Dynamics with Electron Holography

1994 ◽  
Vol 332 ◽  
Author(s):  
Akira Tonomura
Keyword(s):  
Flux Line ◽  
Interference Microscopy ◽  
Electron Holography ◽  
Temperature Changes ◽  
Lorentz Microscopy ◽  
Flux Lines ◽  
Electron Interference ◽  
Time Observation ◽  
Real Time Observation ◽  
Line Movement

ABSTRACTFlux lines in superconducting thin films are observed statically in a holographic electron interference micrograph, and dynamically in a Lorentz micrograph with a “coherent” and 300kV electron beam. In interference microscopy, projected magnetic lines of force in a tilted Nb thin film are observed quantitatively as contour fringes drawn on an in-focus electron micrograph. Whereas in Lorentz microscopy, flux lines are observed as spots with bright and dark contrast pairs due to defocusing of the image. Although the image is blurred due to a large amount of defocusing, this method is suitable for real-time observation. By making the best use of this feature, flux line movement can be observed when the applied magnetic field or the film temperature changes.

Real-time observation of vortex lattices in a superconductor

1993 ◽  
Vol 51 ◽  
pp. 1050-1051
Author(s):  
K. Harada ◽  
T. Matsuda ◽  
J.E. Bonevich ◽  
M. Igarashi ◽  
S. Kondo ◽  
...  
Keyword(s):  
Real Time ◽  
Flux Line ◽  
Electron Holography ◽  
Lorentz Microscopy ◽  
Vortex Lattices ◽  
Flux Lines ◽  
Magnetic Flux Lines ◽  
Time Observation ◽  
Thin Superconductor ◽  
Real Time Observation

Previous observations of magnetic flux-lines (vortex lattices) in superconductors, such as the field distribution of a flux-line, and flux-line dynamics activated by heat and current, have employed the high spatial resolution and magnetic sensitivity of electron holography. And recently, the 2-D static distribution of vortices was also observed by this technique. However, real-time observations of the vortex lattice, in spite of scientific and technological interest, have not been possible due to experimental difficulties. Here, we report the real-time observation of vortex lattices in a thin superconductor, by means of Lorentz microscopy using a 300 kV field emission electron microscope. This technique allows us to observe the dynamic motion of individual vortices and record the events on a VTR system.The experimental arrangement is shown in Fig. 1. A Nb thin film for transmission observation was prepared by chemical etching. The grain size of the film was increased by annealing, and single crystals were observed with a thickness of 50∼90 nm.

Electron holography for magnetic property study of materials

1990 ◽  
Vol 48 (4) ◽  
pp. 392-393
Author(s):  
Akira Tonomura
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Phase Distribution ◽  
Magnetic Domain ◽  
Interference Microscopy ◽  
Electron Holography ◽  
Lorentz Microscopy ◽  
Coherent Field ◽  
Electron Interference ◽  
Intuitive Interpretation

An electron beam is often modulated, only in phase and not in intensity. When the beam passes through a magnetic field or a ferromagnetic thin film which can be regarded as pure phase objects. Therefore, great defocusing is indispensable for magnetic domain observation in Lorentz microscopy. Electron interference microscopy, however, can directly display the phase distribution of an electron beam in an in-focus electron micrograph, and consequently should provide direct information about magnetic fields.The development of a coherent field emission electron beam has opened a way to such a possibility using electron holography in which the phase-amplified phase distribution can be displayed as an interference micrograph. In addition, contour fringes have been interpreted as in-plane magnetic lines of force. Such an intuitive interpretation is possible for the following reason (Fig.1). An incident wavefront is displaced by the vector potential circulating around a magnetic field.

Real-Time Observation of the Interaction between Flux Lines and Defects in a Superconductor by Lorentz Microscopy

1994 ◽  
Vol 33 (Part 1, No. 5A) ◽  
pp. 2534-2540 ◽  
Author(s):  
Ken Harada ◽  
Hiroto Kasai ◽  
Tsuyoshi Matsuda ◽  
Masami Yamasaki ◽  
John E. Bonevich ◽  
...  
Keyword(s):  
Real Time ◽  
Lorentz Microscopy ◽  
Flux Lines ◽  
Time Observation ◽  
Real Time Observation

On the influence of specimen thickness in TEM images of super-conducting vortices

1996 ◽  
Vol 54 ◽  
pp. 724-725
Author(s):  
J. Bonevich ◽  
D. Capacci ◽  
G. Pozzi ◽  
K. Harada ◽  
H. Kasai ◽  
...  
Keyword(s):  
Flux Line ◽  
Analytical Form ◽  
Realistic Model ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Flux Tubes ◽  
Analytical Expression ◽  
Flux Lines ◽  
Normal Core ◽  
Two Parameters

The successful observation of superconducting flux lines (fluxons) in thin specimens both in conventional and high Tc superconductors by means of Lorentz and electron holography methods has presented several problems concerning the interpretation of the experimental results. The first approach has been to model the fluxon as a bundle of flux tubes perpendicular to the specimen surface (for which the electron optical phase shift has been found in analytical form) with a magnetic flux distribution given by the London model, which corresponds to a flux line having an infinitely small normal core. In addition to being described by an analytical expression, this model has the advantage that a single parameter, the London penetration depth, completely characterizes the superconducting fluxon. The obtained results have shown that the most relevant features of the experimental data are well interpreted by this model. However, Clem has proposed another more realistic model for the fluxon core that removes the unphysical limitation of the infinitely small normal core and has the advantage of being described by an analytical expression depending on two parameters (the coherence length and the London depth).

Flux-line observation by electron Holography

1993 ◽  
Vol 51 ◽  
pp. 1024-1025
Author(s):  
Akira Tonomura
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
Magnetic Flux ◽  
Transition Region ◽  
Flux Line ◽  
Electron Holography ◽  
Phase Measurements ◽  
Flux Lines ◽  
Magnetic Flux Lines ◽  
Line Observation

In electron microscopy, the intensity of an electron beam transmitted through an object can be observed. While in electron holography, the phase of the electron beam can also be observed and displayed as an interference micrograph. Using a technique unique to holography, the precision of phase measurements can be increased to 1/100 of the electron wavelength. An interference micrograph of a magnetic object can be interpreted in a straightforward way: Contour fringes directly indicate projected magnetic flux lines and a constant magnetic flux of h/e (= 4 × 10-15 Wb) flows between two adjacent fringes (See Fig. 1).Examples of magnetic recordings are shown in Fig. 2. Flux lines inside and outside of the magnetic tapes, recorded in different ways, can directly and quantitatively be observed as interference micrographs. Figure 2 (a) shows an example of in-plane magnetic recording. Two magnetization streams, pointed in opposite directions, merge and produce vortices in the transition region similar to those produced by streams of water.

Real-time observation of individual vortices in high-Tc superconductors by Lorentz microscopy

2000 ◽  
Vol 332 (1-4) ◽  
pp. 45-50 ◽  
Author(s):  
A Tonomura ◽  
H Kasai ◽  
O Kamimura ◽  
T Matsuda ◽  
K Harada ◽  
...  
Keyword(s):  
Real Time ◽  
High Tc Superconductors ◽  
High Tc ◽  
Lorentz Microscopy ◽  
Time Observation ◽  
Real Time Observation

Electron holography observation of flux-line dynamics

1992 ◽  
Vol 50 (1) ◽  
pp. 68-69 ◽  
Author(s):  
Takaho Yoshida ◽  
Tsuyoshi Matsuda ◽  
Akira Tonomura
Keyword(s):  
Magnetic Field ◽  
Thin Films ◽  
Spatial Resolution ◽  
Flux Line ◽  
Electrical Current ◽  
Electron Holography ◽  
Video Tape ◽  
Flux Lines ◽  
Flux Motion ◽  
Individual Flux

With the sufficient spatial resolution and magnetic sensitivity, Electron holography has opened a new way to directly observe the flux lines in superconductors. It has successfully shown the detailed magnetic field distribution of individual flux lines penetrating Pb thin films. This technique also excels at observing flux line dynamics. By taking the holograms with a TV camera and recording them on a video tape, it became possible to observe the flux motion microscopically and continuously. Using this technique, the present study will demonstrate the thermally excited and the electrical current induced flux line dynamics.

The effect of core size on the holographic interference images of superconducting fluxons in tilted specimens

1993 ◽  
Vol 51 ◽  
pp. 1224-1225
Author(s):  
G. Pozzi ◽  
J.E. Bonevich ◽  
A. Tonomura
Keyword(s):  
Electron Holography ◽  
Electron Optics ◽  
Core Size ◽  
Flux Tubes ◽  
Lorentz Microscopy ◽  
Flux Lines ◽  
Advanced Phase ◽  
Transmission Electron ◽  
Phase Sensitive ◽  
Set Up

Recently, observations of quantized flux lines in thin superconducting specimens have been successfully carried out in transmission electron microscopy by means of standard methods of Lorentz microscopy and also by electron holography. The breakthrough with respect to the previous unsuccessful attempts is represented by the fact that the specimen is observed tilted with respect both to the electron beam and the ancillary magnetic field that is used to introduce and stabilize the fluxons in the specimen.Although a reduction of the phase difference with respect to the optimum situation of fluxons perpendicular to the beam is expected in this set-up, it has nonetheless been possible to ascertain by means of a simple model that this reduction is not below the detectability limit that can be reached by the most advanced phase sensitive methods available today in electron optics, such as electron holography. However calculations have been carried out so far either for the single fluxon case, taking into account also its core structure, or for an array of 25 flux tubes (i.e. fluxons with negligible core size) arranged in a triangular lattice.

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