Microstruoture-Property Relationships in Magenqubnch Magnets

1987 ◽  
Vol 96 ◽  
Author(s):  
Raja K. Rishra
Keyword(s):  
Melt Spinning ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Processing Parameters ◽  
Second Phase ◽  
Lorentz Microscopy ◽  
Transmission Electron ◽  
Melt Spun ◽  
Magnetic Domain Walls ◽  
Two Phases

ABSTRACTTransmission electron microscopy has been used to characterize the microstructure of Nd-Fe-B magnets produced by melt-spinning and subsequent hot-pressing/die-upsetting. For a material of starting composition Nd.135Fe.815B.05, the basic microstructure od melt-spun, hot-pressed and dieupset magnets consists of two phases. In the optimally processed melt-spun ribbons and hot-pressed samples, small and randomly oriented Nd2Fe14B grains are surrounded by a thin noncrystalline Nd-rlch phase. The die-upset material consists of closely stacked flat Nd2Fe14B grains surrounded by a second phase of approximate composition Nd7Fe3. No Nd11Fe4B4 phase is observed in these materials, but it can form if the chemical composition and/or processing parameters are varied. In all these materials, Lorentz microscopy reveals that magnetic domain walls are pinned by the second phase. The differences in the hard magnetic properties of the three kinds of MAGNEQUENCH magnets closely correlate with the differences in the distribution of Nd2Fe14B crystallites and the pinning sites.

scholarly journals Aberration Corrected Lorentz Microscopy to Investigate Magnetic Domain Walls in Co-Pt Nano-Chessboards

2017 ◽  
Vol 23 (S1) ◽  
pp. 454-455 ◽  
Author(s):  
Isha Kashyap ◽  
Jerrold A. Floro ◽  
Yongmei M. Jin ◽  
Marc De Graef
Keyword(s):  
Domain Walls ◽  
Magnetic Domain ◽  
Lorentz Microscopy ◽  
Magnetic Domain Walls ◽  
Aberration Corrected

Lorentz Microscopy: Effect of Tilting on Magnetic Domains in Single Crystal Iron Films

1968 ◽  
Vol 26 ◽  
pp. 388-389
Author(s):  
L. F. Allard ◽  
A. P. Rowe ◽  
P. L. Fan
Keyword(s):  
Single Crystal ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Objective Lens ◽  
Pole Piece ◽  
Magnetic Domains ◽  
Iron Films ◽  
Lorentz Microscopy ◽  
Magnetic Domain Walls ◽  
Microscopy Techniques

In order to observe magnetic domain walls by Lorentz microscopy techniques it is often necessary either to operate the microscope with the objective lens off, thus severely limiting the magnification, or to move the specimen from its usual position or make some other modification so that the field to which it is subjected is not so strong that it saturates the specimen. However, conditions in the JEM-6A have proved favorable for observation of domains in single crystal iron films by the out-of-focus method without any modifications, using either the regular specimen stage with the small bore pole piece or the tilting stage with the large bore pole piece. The tilting stage is particularly useful for these studies because the domains are very sensitive to small differences in inclination in the field.

Observations by Lorentz microscopy of movements of magnetic domain walls in amorphous Fe78B13Si9 alloys

1994 ◽  
Vol 133 (1-3) ◽  
pp. 77-81 ◽  
Author(s):  
B. Astie ◽  
M. Fagot ◽  
C. Beraud ◽  
J. Degauque ◽  
E. Ferrara ◽  
...  
Keyword(s):  
Domain Walls ◽  
Magnetic Domain ◽  
Lorentz Microscopy ◽  
Magnetic Domain Walls

The direct determination of magnetic domain wall profiles using a split detector STEM

1978 ◽  
Vol 36 (1) ◽  
pp. 466-467
Author(s):  
J.N. Chapman ◽  
P.E. Batson ◽  
E.M. Waddell ◽  
R.P. Ferrier
Keyword(s):  
Electron Microscope ◽  
Domain Wall ◽  
Transmission Electron Microscope ◽  
Domain Walls ◽  
Photographic Plate ◽  
Magnetic Domain ◽  
Direct Determination ◽  
Quantitative Information ◽  
Scanning Transmission Electron Microscope ◽  
Transmission Electron

By far the most commonly used mode of Lorentz microscopy in the examination of ferromagnetic thin films is the Fresnel or defocus mode. Use of this mode in the conventional transmission electron microscope (CTEM) is straightforward and immediately reveals the existence of all domain walls present. However, if such quantitative information as the domain wall profile is required, the technique suffers from several disadvantages. These include the inability to directly observe fine image detail on the viewing screen because of the stringent illumination coherence requirements, the difficulty of accurately translating part of a photographic plate into quantitative electron intensity data, and, perhaps most severe, the difficulty of interpreting this data. One solution to the first-named problem is to use a CTEM equipped with a field emission gun (FEG) (Inoue, Harada and Yamamoto 1977) whilst a second is to use the equivalent mode of image formation in a scanning transmission electron microscope (STEM) (Chapman, Batson, Waddell, Ferrier and Craven 1977), a technique which largely overcomes the second-named problem as well.

Lorentz microscopy study of magnetic domain walls in Fe-Cr-Co alloys

1978 ◽  
Vol 36 (1) ◽  
pp. 462-463
Author(s):  
Yalcin Belli
Keyword(s):  
Domain Walls ◽  
Magnetic Domain ◽  
Microscopy Study ◽  
Ferromagnetic Phase ◽  
Stable Phase ◽  
Magnetic Domains ◽  
Lorentz Microscopy ◽  
Magnetic Hardening ◽  
Electron Microscopes ◽  
Co Alloys

Fe-Cr-Co alloys have great technological potential to replace Alnico alloys as hard magnets. The relationship between the microstructures and the magnetic properties has been recently established for some of these alloys. The magnetic hardening has been attributed to the decomposition of the high temperature stable phase (α) into an elongated Fe-rich ferromagnetic phase (α1) and a weakly magnetic or non-magnetic Cr-rich phase (α2). The relationships between magnetic domains and domain walls and these different phases are yet to be understood. The TEM has been used to ascertain the mechanism of magnetic hardening for the first time in these alloys. The present paper describes the magnetic domain structure and the magnetization reversal processes in some of these multiphase materials. Microstructures to change properties resulting from, (i) isothermal aging, (ii) thermomagnetic treatment (TMT) and (iii) TMT + stepaging have been chosen for this investigation. The Jem-7A and Philips EM-301 transmission electron microscopes operating at 100 kV have been used for the Lorentz microscopy study of the magnetic domains and their interactions with the finely dispersed precipitate phases.

Magnetic Material Observation Assembly for Tem with a Eucentric Goniometer

1976 ◽  
Vol 34 ◽  
pp. 540-541
Author(s):  
K. Shi rota ◽  
A. Yonezawa ◽  
K. Shibatomi ◽  
T. Yanaka
Keyword(s):  
Magnetic Material ◽  
Electron Microscope ◽  
Magnetic Domain ◽  
Objective Lens ◽  
Magnetic Domains ◽  
Lorentz Microscopy ◽  
Transmission Electron ◽  
Correction Of Astigmatism ◽  
Single Orientation ◽  
Conventional Transmission Electron Microscope

As is well known, it is not so easy to operate a conventional transmission electron microscope for observation of magnetic materials. The reason is that the instrument requires re-alignment of the axis and re-correction of astigmatism after each specimen shift, as the lens field is greatly disturbed by the specimen. With a conventional electron microscope, furthermore, it is impossible to observe magnetic domains, because the specimen is magnetized to single orientation by the lens field. The above mentioned facts are due to the specimen usually being in the lens field. Thus, special techniques or systems are usually required for magnetic material observation (especially magnetic domain observation), for example, the technique to switch off the objective lens current and Lorentz microscopy. But these cannot give high image quality and wide magnification range, and furthermore Lorentz microscopy is very complicated.

Temperature Dependence of Magnetic Domains and Wall Structures

1972 ◽  
Vol 30 ◽  
pp. 496-497
Author(s):  
Sonoko Tsukahara ◽  
Tadami Taoka ◽  
Hisao Nishizawa
Keyword(s):  
Temperature Dependence ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Iron Film ◽  
Objective Lens ◽  
Lorentz Microscopy ◽  
Domain Structures ◽  
Wall Structures ◽  
Crystal Films ◽  
Metallurgical Structure

The high voltage Lorentz microscopy was successfully used to observe changes with temperature; of domain structures and metallurgical structures in an iron film set on the hot stage combined with a goniometer. The microscope used was the JEM-1000 EM which was operated with the objective lens current cut off to eliminate the magnetic field in the specimen position. Single crystal films with an (001) plane were prepared by the epitaxial growth of evaporated iron on a cleaved (001) plane of a rocksalt substrate. They had a uniform thickness from 1000 to 7000 Å.The figure shows the temperature dependence of magnetic domain structure with its corresponding deflection pattern and metallurgical structure observed in a 4500 Å iron film. In general, with increase of temperature, the straight domain walls decrease in their width (at 400°C), curve in an iregular shape (600°C) and then vanish (790°C). The ripple structures with cross-tie walls are observed below the Curie temperature.

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