Quantification of micromagnetic structure from Lorentz micrographs

Defocused imaging of magnetic domain structures is a well-known technique to observe the micromagnetic structures in ferromagnetic thin films. Nevertheless, Lorentz microscopy images are rarely subject to a quantitative evaluation of micromagnetic parameters. In this paper, we offer a new method for quantitative evaluation of ripple wavelengths and ripple angle from Lorentz microscopy images carried out on soft magnetic Ni81Fe19 films. The work was carried out using a Philips CM30 electron microscope with a combined Twin/Lorentz lens.The experiments were performed on thin ferromagnetic films of a Ni81Fe19 alloy. Due to the internal magnetic induction within the specimens, the partial electron waves experience a phase shift proportional to the local in-plane magnetic induction , the specimen's thickness t and the lateral distance x from an arbitrarily chosen point of zero phase shift on the specimen. This phase shift can then be imaged using phase contrast methods similar to HREM. Since the phase shifts and the corresponding deflection angles can be very small, a large defocus is necessary to obtain contrast. This large defocus gives rise to an oscillating phase contrast transfer function for the spatial frequencies under observation as well as to a damping envelope for higher spatial frequencies.

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Differential phase contrast Lorentz microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100176927 ◽

1990 ◽

Vol 48 (4) ◽

pp. 758-759

Author(s):

Ian R. McFadyen

Keyword(s):

Electron Beam ◽

Phase Shift ◽

Magnetic Induction ◽

Phase Contrast ◽

Magnetic Films ◽

Electron Wave ◽

Lorentz Microscopy ◽

Differential Phase ◽

Phase Derivative ◽

Differential Phase Contrast

Transmission electron microscopy can provide high spatial resolution information on domain structures in thin magnetic films provided the interaction between the electron beam and the magnetic sample is correctly utilised: As an electron beam passes through a magnetic sample it suffers a phase shift due to the magnetic induction of the sample and the associated stray fields. The derivative of this phase shift is a direct measure of the in-plane magnetic induction integrated along the electron trajectory, Therefore measurement of this phase derivative would provide the integrated in-plane induction directly. The conventional phase contrast techniques of Fresnel and Foucault Lorentz microscopy provide image contrast which has a very non-linear relationship to the above mentioned phase derivative. Differential phase contrast Lorentz microscopy (DPC), on the other hand, does provide direct, high resolution information on the phase derivative of the electron wave as it leaves tile sample. In this technique a focused probe of electrons is scanned cross the sample and a position sensitive detector in the far field measures two orthogonal components of the probe deflection angle at each point in the scan. This corresponds to the derivative of the phase of the electron wave as it leaves the sample, and thus to the integral of the in-plane induction at each point.

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Temperature Dependence of Magnetic Domains and Wall Structures

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010009573x ◽

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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New challenges to image processing posed by cryo-Electron microscopy of single particles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100086416 ◽

1991 ◽

Vol 49 ◽

pp. 422-423

Author(s):

Joachim Frank

Keyword(s):

Electron Microscopy ◽

Phase Contrast ◽

Particle Orientation ◽

Single Particles ◽

Contrast Transfer Function ◽

Virtual Absence ◽

Cryo Electron Microscopy ◽

Spatial Frequencies ◽

New Challenges ◽

Particle Images

Compared with images of negatively stained single particle specimens, those obtained by cryo-electron microscopy have the following new features: (a) higher “signal” variability due to a higher variability of particle orientation; (b) reduced signal/noise ratio (S/N); (c) virtual absence of low-spatial-frequency information related to elastic scattering, due to the properties of the phase contrast transfer function (PCTF); and (d) reduced resolution due to the efforts of the microscopist to boost the PCTF at low spatial frequencies, in his attempt to obtain recognizable particle images.

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Fourier spectrum analysis of phase contrast of support film

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010010799x ◽

1978 ◽

Vol 36 (1) ◽

pp. 170-171

Author(s):

Tetsuo Oikawa ◽

Fumiko Ishigaki ◽

Kiichi Hojou ◽

Koichi Kanaya

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Phase Shift ◽

Phase Contrast ◽

Fourier Transforms ◽

Spherical Aberration ◽

High Resolution Electron Microscopy ◽

Spatial Frequencies ◽

Resolution Electron ◽

Atomic Phase

In high resolution electron microscopy, it is most important to determine the defocus of electron micrographs of amorphous support films. The variation of spatial frequencies of phase contrast of support films was obtained from the phase shift of the electron waves caused by defocus and spherical aberration as well as the atomic phase, which are demonstrated by use of optical Fourier transforms. The spatial frequencies of phase contrast of films of tungsten, prepared by ion bombardment, which are useful as support films for high resolution electron microscopy, has been discussed analytically.Taking account of atomic phase shift, the transfer function, which was originally presented by Thon (1966), was modified. Optical Fourier transforms are in similar to the calculated Fourier transforms of corre- sponding computed images. Accordingly, it turned out that the atomic phase shift should not be neglected. The thickness of tungsten film, in case of less than 2 nm thickness, can be determined by comparing the optical Fourier transforms with the calculated ones.

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Atomic Structure-Sensitive Magnetic Domain Structures of Thin Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100117960 ◽

1985 ◽

Vol 43 ◽

pp. 206-209

Author(s):

S. Tsukahara

Keyword(s):

Thin Films ◽

Magnetic Properties ◽

Domain Walls ◽

Magnetic Domain ◽

Quarter Century ◽

Specimen Handling ◽

Lorentz Microscopy ◽

Domain Structures ◽

Structure Sensitive ◽

Direct Interpretation

Transmission electron microscopy, TEM, that can serve for observation of both atomic and magnetic structures is useful to investigate structure sensitive magnetic properties. It is most effective when it is applied to thin films for which direct interpretation of the results is possible without considering additional effects through specimen handling for TEM use and modification of dimension dependent magnetic properties.Transmission Lorentz microscopy, TLM, to observe magnetic domains has been known for a quarter century. Among TLM modes the defocused mode has been most popular due to its simple way of operation. Recent development of TEM made it possible that an average instrument commercially available could be easily operated at any TLM modes to produce high quality images. This paper mainly utilizes the Foucault mode to investigate domain walls and magnetization ripples as the finest details of domain structure.

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Magnetic domain structures in Co–Ni–Al shape memory alloys studied by Lorentz microscopy and electron holography

Acta Materialia ◽

10.1016/s1359-6454(02)00061-7 ◽

2002 ◽

Vol 50 (8) ◽

pp. 2173-2184 ◽

Cited By ~ 84

Author(s):

Y Murakami ◽

D Shindo ◽

K Oikawa ◽

R Kainuma ◽

K Ishida

Keyword(s):

Shape Memory Alloys ◽

Shape Memory ◽

Magnetic Domain ◽

Electron Holography ◽

Lorentz Microscopy ◽

Domain Structures

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Magnetic Domains and Domain Wall Pinning in Nanocrystalline Ni-P

Microscopy and Microanalysis ◽

10.1017/s1431927600032281 ◽

2001 ◽

Vol 7 (S2) ◽

pp. 1242-1243

Author(s):

J.P. Zhang ◽

Y.X. Guo ◽

J.S. Speck

Keyword(s):

Magnetic Domain ◽

Control Mode ◽

Objective Lens ◽

Magnetic Domains ◽

Lorentz Microscopy ◽

Domain Structures ◽

Resolution Electron ◽

Alloy Material ◽

Electron Imaging ◽

Fcc Structure

Magnetic domain structures in a Ni-5at%P alloy have been examined using Lorentz microscopy in Fresnel mode in a JEOL 2010TEM. with electron diffraction and high resolution electron imaging, the Ni-P alloy material is seen to be of FCC structure and composed of nanometer-sized grains (< 4nm in diameter), which is about 2 orders less in size than that of a single magnetic domain.The TEM specimen was prepared using jet polishing method. Before introducing the specimen into the microscope, the objective lens was turned off in a free lens control mode to ensure that the domain structures in the specimen remain unaffected. The objective mini-lens was used to perform Lorentz imaging with out-focus method.Stripe domains were observed. The width of these stripes is about 0.2 micron. But the length of these domains varies, sometime up to several microns. The stripe domains are grouped, which are near parallel one to the other.

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

MATERIALS TRANSACTIONS ◽

10.2320/matertrans.46.974 ◽

2005 ◽

Vol 46 (5) ◽

pp. 974-977 ◽

Cited By ~ 7

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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Zernike Phase Contrast Electron Microscopy with a Spherically Corrected Foil Lens

Microscopy and Microanalysis ◽

10.1017/s1431927610000462 ◽

2010 ◽

Vol 16 (4) ◽

pp. 441-444 ◽

Cited By ~ 3

Author(s):

Dieter Typke

Keyword(s):

Electron Microscopy ◽

Phase Shift ◽

Phase Contrast ◽

Thin Foil ◽

Objective Lens ◽

Lens System ◽

Strong Phase ◽

Spatial Frequencies ◽

The Way

AbstractA lens system is proposed that not only provides spherical correction of the objective lens by charges that are induced on a thin foil, in the way proposed in a paper by Otto Scherzer [Optik56(2), 133–147, 1980], but also provides Zernike phase contrast by means of an appropriate phase shift of the scattered electrons within the foil. This system has the potential to provide strong phase contrast from very low spatial frequencies to frequencies above 1/(100 pm).

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