In situ observations of domain structures and magnetic flux distributions in Mn-Zn and Ni-Zn ferrites by Lorentz microscopy and electron holography

2007 ◽  
Vol 56 (1) ◽  
pp. 7-16 ◽  
Author(s):  
T. Kasahara ◽  
D. Shindo ◽  
H. Yoshikawa ◽  
T. Sato ◽  
K. Kondo
Keyword(s):  
Magnetic Flux ◽  
Electron Holography ◽  
Lorentz Microscopy ◽  
Domain Structures ◽  
In Situ Observations

scholarly journals Flux Mapping and Magnetic Behavior of Grain Boundaries in Nd-Fe-B Magnets

1999 ◽  
Vol 589 ◽  
Author(s):  
V.V. Volkov ◽  
Yimei Zhu
Keyword(s):  
Magnetic Flux ◽  
Grain Boundaries ◽  
Domain Walls ◽  
Quantitative Description ◽  
Magnetic Behavior ◽  
Local Variation ◽  
Smooth Transition ◽  
Lorentz Microscopy ◽  
Hard Magnets

AbstractAdvanced Fresnel- & Foucault-Lorentz microscopy were applied to analyze magnetic behavior of the grain boundaries in Nd-Fe-B hard magnets. In-situ TEM magnetizing experiments combined with these imaging methods revealed the process of magnetization reversal in polycrystalline sintered and die-upset Nd-Fe-B under various magnetic fields. Fine details of magnetic flux distribution, derived from the magnetic interferograms created by phase-coherent Foucault imaging, provide a quantitative description of the local variation of magnetic flux. Our study suggests that the grain boundaries play an important multi-functional role in the reversal of magnetization, by acting as (a) pinning centers of domain walls, (b) centers of nucleation of reversal domains, and (c) sinks or sources for migrating magnetostatic charges and/or dipoles. They also ensure a smooth transition for irreversible remagnetization in polycrystalline samples.

Observations of Magnetic Domain Structure Change in Nd2Fe14B Magnets at Elevated Temperature with External Magnetic Field by Lorentz Microscopy

2015 ◽  
Vol 1754 ◽  
pp. 31-36 ◽  
Author(s):  
Toshimasa Suzuki ◽  
Koichi Kawahara ◽  
Haruka Tanaka ◽  
Kimihiro Ozaki
Keyword(s):  
Elevated Temperature ◽  
Domain Wall ◽  
Wall Motion ◽  
Magnetic Domain ◽  
Domain Wall Motion ◽  
Magnetic Domain Wall ◽  
Lorentz Microscopy ◽  
Pinning Effect ◽  
In Situ Observations

ABSTRACTIn this study, we conducted the in-situ observations of the magnetic domain structure change in Nd2Fe14B magnets at elevated temperature by transmission electron microscopy (TEM) / Lorentz microscopy. The in-situ observations in Nd2Fe14B magnets revealed that the magnetization reversal easily occurred at the elevated temperature. At more than 180°C, the magnetic domain wall motion could be observed by applying the magnetic field of less than 20 mT. The motion of the magnetic domain wall was discontinuous and the domain wall jumped to one grain boundary to the neighboring grain boundary at 180°C. On the other hand, the continuous domain wall motion within grain interior as well as discontinuous domain wall motion was observed at 225°C, and some grain boundaries showed still strong pinning effect even at 225°C. The temperature dependence of the pinning effect of grain boundaries would not uniform.

scholarly journals Direct Observation of Nanoscale Magnetization Reversal and Spin Dynamics Using In-Situ Lorentz Microscopy and Electron Holography

2010 ◽  
Vol 16 (S2) ◽  
pp. 576-577
Author(s):  
L Huang ◽  
Y Zhu
Keyword(s):  
Direct Observation ◽  
Magnetization Reversal ◽  
Spin Dynamics ◽  
Electron Holography ◽  
Lorentz Microscopy

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

scholarly journals Small-scale Magnetic Flux Ropes with Field-aligned Flows via the PSP In Situ Observations

2021 ◽  
Vol 914 (2) ◽  
pp. 108
Author(s):  
Yu Chen ◽  
Qiang Hu ◽  
Lingling Zhao ◽  
Justin C. Kasper ◽  
Jia Huang
Keyword(s):  
Magnetic Flux ◽  
Small Scale ◽  
Magnetic Flux Ropes ◽  
Flux Ropes ◽  
In Situ Observations

scholarly journals Electron Microscopy Imaging of Flux Pinning Defects in YBCO Superconductors

2021 ◽  
Author(s):  
◽  
Anne-Hélène Puichaud
Keyword(s):  
Electron Microscopy ◽  
Magnetic Flux ◽  
Critical Current ◽  
Flux Pinning ◽  
Coated Conductors ◽  
Electron Holography ◽  
Coated Conductor ◽  
Lorentz Microscopy ◽  
Superconducting Wires ◽  
Ybco Superconductors

<p>High-temperature superconductors are of great interest because they can transport electrical current without loss. For real-world applications, the amount of current, known as the critical current Ic, that can be carried by superconducting wires is the key figure of merit. Large Ic values are necessary to off-set the higher cost of these wires. The factors that improve Ic (microstructure/performance relationship) in the state-of-the-art coated conductor wires based on YBa₂Cu₃O₇ (YBCO) are not fully understood. However, microstructural defects that immobilise (or pin) tubes of magnetic flux (known as vortices) inside the coated conductors are known to play a role in improving Ic. In this thesis, the vortex-defect interaction in YBCO superconductors was investigated with high-end transmission electron microscopy (TEM) techniques using two approaches.  First, the effect of dysprosium (Dy) addition and oxygenation temperature on the microstructure and critical current were investigated in detail. Changing only the oxygenation temperature leads to many microstructural changes in pure YBCO coated conductors. It was found that Dy addition reduces the sensitivity of the YBCO to the oxygenation temperature, in particular it lowers the microstructural disorder while maintaining the formation of nanoparticles, which both contribute to the enhancement of Ic.  In the second approach, two TEM based techniques (off-axis electron holography and Lorentz microscopy) were used to study the magnetic flux vortices. Vortex imaging was attempted with a TEM operated at 300 kV on both a YBCO crystal as well as a YBCO coated conductor. Many challenges were encountered including sample preparation, inhomogeneity, and geometry, in addition to the need to perform measurements at cryogenic temperatures. Although vortices were not able to be observed in the coated conductors, tentative observation of vortices in a YBCO crystal was made using Lorentz microscopy. Improvements for future electron holography experiments on YBCO at low voltage are suggested. This work represents a pioneering step towards directly imaging vortices in YBCO using more widely available microscopes with the aim of better understanding flux pinning to ultimately boost Ic in superconducting wires.</p>

scholarly journals Magnetic Domain Structures in Electrical Steel Sheets Studied by Lorentz Microscopy and Electron Holography

2005 ◽  
Vol 46 (5) ◽  
pp. 974-977 ◽  
Author(s):  
Zentaro Akase ◽  
Young-Gil Park ◽  
Daisuke Shindo ◽  
Toshiro Tomida ◽  
Hiroyosi Yashiki ◽  
...  
Keyword(s):  
Electrical Steel ◽  
Magnetic Domain ◽  
Electron Holography ◽  
Lorentz Microscopy ◽  
Steel Sheets ◽  
Domain Structures ◽  
Electrical Steel Sheets
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