Observation of Ferrimagnetic Domain Walls in CoFe2O4 With A High Voltage T.E.M.

1973 ◽  
Vol 31 ◽  
pp. 26-27
Author(s):  
L. C. De Jonghe
Keyword(s):  
Domain Wall ◽  
Ceramic Material ◽  
High Voltage ◽  
Domain Walls ◽  
Magnetic Ordering ◽  
Objective Lens ◽  
Spinel Type ◽  
Equal Energy ◽  
Cobalt Ferrites ◽  
Regular Position

Cobalt ferrites are ferrimagnetic oxides of the spinel type, exhibiting magnetic ordering along <100>. Ferrimagnetic domain walls have been observed in this ceramic material with the specimens in the regular position. Even though the field of the objective lens is quite high ∼7 k gauss) domain walls may be observed if the specimens are symmetrically oriented with respect to the field direction of the objective lens, so that adjacent domains have approximately equal energy. Ill are such orientations for cobalt ferrites. Under these conditions, only ╥/2 domain walls are expected. Such ╥/2 ferrimagnetic domain walls are shown in Fig. 1. Since magnetostriction accompanies magnetic ordering, the domain wall boundaries are also coherent twin boundaries which can be imaged with the specimen in focus.

STEM of order and dynamics in novel magnetic materials

1993 ◽  
Vol 51 ◽  
pp. 1026-1027
Author(s):  
Marian Mankos ◽  
J.M. Cowley ◽  
R.V. Chamberlin ◽  
M. Scheinfein ◽  
J.D. Ayers
Keyword(s):  
Magnetic Field ◽  
Magnetic Structure ◽  
Phase Contrast ◽  
Domain Walls ◽  
Detection System ◽  
Magnetic Ordering ◽  
Dark Field ◽  
Objective Lens ◽  
Lorentz Microscopy ◽  
Differential Phase Contrast

The new detection system of the HB5 STEM enables the operation of the microscope in a variety of modes. If the specimen is placed inside the objective lens, high resolution bright and dark field images revealing the microstructure can be obtained. Since the specimen is located in a high magnetic field, magnetic ordering phenomena are disturbed and no magnetic structure contrast is observed. In the out-of-field position, magnetic structure may be revealed in the Fresnel and Differential Phase Contrast modes of Lorentz Microscopy. Fresnel images are obtained with a static beam, i.e. the scanning coils are not excited. In the Fresnel mode the objective lens focus is changed slightly and domain walls appear in the shadow image as dark and bright lines, switching contrast when the objective lens is changed between overfocussing and underfocussing. Electrons, passing through the sample, are deflected by the Lorentz force and appear to converge towards or diverge from the domain walls.

The Reduction of Chromatic Aberrations Due to Instrumental Instabilities

1971 ◽  
Vol 29 ◽  
pp. 14-15
Author(s):  
J. S. Lally ◽  
R. Evans
Keyword(s):  
Electron Microscope ◽  
High Voltage ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Usual Practice ◽  
Voltage Electron ◽  
Short Focal Length ◽  
Chromatic Aberrations ◽  
Electron Microscopes

One of the instrumental factors often limiting the resolution of the electron microscope is image defocussing due to changes in accelerating voltage or objective lens current. This factor is particularly important in high voltage electron microscopes both because of the higher voltages and lens currents required but also because of the inherently longer focal lengths, i.e. 6 mm in contrast to 1.5-2.2 mm for modern short focal length objectives.The usual practice in commercial electron microscopes is to design separately stabilized accelerating voltage and lens supplies. In this case chromatic aberration in the image is caused by the random and independent fluctuations of both the high voltage and objective lens current.

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.

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.

100 KV Scanning Microscope

1972 ◽  
Vol 30 ◽  
pp. 472-473 ◽  
Author(s):  
A. V. Crewe ◽  
M. W. Retsky
Keyword(s):  
High Voltage ◽  
Voltage Divider ◽  
Electron Gun ◽  
Objective Lens ◽  
Parallel Beam ◽  
Emission Point ◽  
Error Amplifier ◽  
External Reference ◽  
Scanning Transmission ◽  
Transmission Microscope

A 100 kv scanning transmission microscope has been built. Briefly, the design is as follows: The electron gun consists of a field emission point and a 3 cm Butler gun. The beam has a crossover outside the gun and is collimated by a condenser lens.The parallel beam passes through a defining aperture and is focused by the objective lens onto the specimen. The elastic electrons are detected by two annular detectors, each subtending a different angle, and the unscattered and inelastic electrons are collected by a third detector. The spectrometer that will separate the inelastic and unscattered electrons has not yet been built.The lens current supplies are stable to within one part per million per hour and have been described elsewhere.The high voltage is also stable to 1 ppm/hr. It consists of the raw supply from a 100 kv Spellman power supply controlled by an external reference voltage, high voltage divider, and error amplifier.

Magnetic Domain Observation of an Amorphous Fe-Si-B Ribbon by Means of a High Voltage Scanning Electron Microscope

1981 ◽  
Vol 39 ◽  
pp. 320-321
Author(s):  
K. Tsuno ◽  
Y. Harada ◽  
T. Sato
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
High Voltage ◽  
Amorphous Ribbon ◽  
Image Resolution ◽  
Objective Lens ◽  
Magnetic Domains ◽  
Scattered Electron ◽  
Voltage Scanning ◽  
Scanning Electron

Magnetic domains of ferromagnetic amorphous ribbon have been observed using Bitter powder method. However, the domains of amorphous ribbon are very complicated and the surface of ribbon is not flat, so that clear domain image has not been obtained. It has been desired to observe more clear image in order to analyze the domain structure of this zero magnetocrystalline anisotropy material. So, we tried to observe magnetic domains by means of a back-scattered electron mode of high voltage scanning electron microscope (HVSEM).HVSEM method has several advantages compared with the ordinary methods for observing domains: (1) high contrast (0.9, 1.5 and 5% at 50, 100 and 200 kV) (2) high penetration depth of electrons (0.2, 1.5 and 8 μm at 50, 100 and 200 kV). However, image resolution of previous HVSEM was quite low (maximum magnification was less than 100x), because the objective lens cannot be excited for avoiding the application of magnetic field on the specimen.

The need of electron microscopy in the study of domains and domain walls in ferroelectrics

1994 ◽  
Vol 52 ◽  
pp. 550-551
Author(s):  
Wenwu Cao
Keyword(s):  
Domain Wall ◽  
Domain Walls ◽  
High Mobility ◽  
Continuum Theory ◽  
Polarization Vector ◽  
Ferroelectric Materials ◽  
Dielectric Constants ◽  
Nonlocal Coupling ◽  
Cubic Symmetry ◽  
Gradient Energy

Domain structures play a key role in determining the physical properties of ferroelectric materials. The formation of these ferroelectric domains and domain walls are determined by the intrinsic nonlinearity and the nonlocal coupling of the polarization. Analogous to soliton excitations, domain walls can have high mobility when the domain wall energy is high. The domain wall can be describes by a continuum theory owning to the long range nature of the dipole-dipole interactions in ferroelectrics. The simplest form for the Landau energy is the so called ϕ model which can be used to describe a second order phase transition from a cubic prototype,where Pi (i =1, 2, 3) are the components of polarization vector, α's are the linear and nonlinear dielectric constants. In order to take into account the nonlocal coupling, a gradient energy should be included, for cubic symmetry the gradient energy is given by,

A new method for the observation of Type II magnetic contrast

1990 ◽  
Vol 48 (4) ◽  
pp. 764-765
Author(s):  
R.P. Ferrier ◽  
S. McVitie
Keyword(s):  
Domain Walls ◽  
Incident Beam ◽  
Objective Lens ◽  
Type Ii ◽  
Backscattering Coefficient ◽  
Magnetic Contrast ◽  
Standard Geometry ◽  
Backscattered Electron ◽  
Imaging Performance ◽  
Good Probe

Type II magnetic contrast was first observed by Philibert and Tixier and relies on the change in the effective backscattering coefficient due to interaction of the scattered electrons within the specimen and the local magnetic induction (for a review see Tsuno). Depending on the tilt of the specimen and the position of the backscattered electron detector(s), contrast due to the presence of either or both domains and domain walls can be obtained; in the case of the latter, the standard geometry is for the specimen to be normal to the incident beam and the detectors are positioned above it and close to the optic axis. This is the geometry adopted in our studies, which used a JEOL 2000FX with a special split objective lens polepiece; this permitted the specimen to be in magnetic field-free space, the separate lens gaps above and below allowing good probe forming capabilities combined with excellent Lorentz imaging performance. A schematic diagram is shown in Fig. 1.

scholarly journals Giant conductivity of mobile non-oxide domain walls

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
S. Ghara ◽  
K. Geirhos ◽  
L. Kuerten ◽  
P. Lunkenheimer ◽  
V. Tsurkan ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Domain Wall ◽  
Domain Walls ◽  
Building Blocks ◽  
External Fields ◽  
Tail Domain ◽  
Oxide Electronics ◽  
Domain Wall Mobility ◽  
Conductance Changes ◽  
Wall Mobility

AbstractAtomically sharp domain walls in ferroelectrics are considered as an ideal platform to realize easy-to-reconfigure nanoelectronic building blocks, created, manipulated and erased by external fields. However, conductive domain walls have been exclusively observed in oxides, where domain wall mobility and conductivity is largely influenced by stoichiometry and defects. Here, we report on giant conductivity of domain walls in the non-oxide ferroelectric GaV4S8. We observe conductive domain walls forming in zig-zagging structures, that are composed of head-to-head and tail-to-tail domain wall segments alternating on the nanoscale. Remarkably, both types of segments possess high conductivity, unimaginable in oxide ferroelectrics. These effectively 2D domain walls, dominating the 3D conductance, can be mobilized by magnetic fields, triggering abrupt conductance changes as large as eight orders of magnitude. These unique properties demonstrate that non-oxide ferroelectrics can be the source of novel phenomena beyond the realm of oxide electronics.

scholarly journals Subsystem domination influence on magnetization reversal in designed magnetic patterns in ferrimagnetic Tb/Co multilayers

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Łukasz Frąckowiak ◽  
Feliks Stobiecki ◽  
Gabriel David Chaves-O’Flynn ◽  
Maciej Urbaniak ◽  
Marek Schmidt ◽  
...  
Keyword(s):  
Domain Wall ◽  
Magnetization Reversal ◽  
Domain Walls ◽  
Compensation Point ◽  
Relative Sign ◽  
Reversal Process ◽  
Effective Magnetization ◽  
Domain Wall Propagation ◽  
Characteristic Features ◽  
Magnetization Reversal Process

AbstractRecent results showed that the ferrimagnetic compensation point and other characteristic features of Tb/Co ferrimagnetic multilayers can be tailored by He+ ion bombardment. With appropriate choices of the He+ ion dose, we prepared two types of lattices composed of squares with either Tb or Co domination. The magnetization reversal of the first lattice is similar to that seen in ferromagnetic heterostructures consisting of areas with different switching fields. However, in the second lattice, the creation of domains without accompanying domain walls is possible. These domain patterns are particularly stable because they simultaneously lower the demagnetizing energy and the energy associated with the presence of domain walls (exchange and anisotropy). For both lattices, studies of magnetization reversal show that this process takes place by the propagation of the domain walls. If they are not present at the onset, the reversal starts from the nucleation of reversed domains and it is followed by domain wall propagation. The magnetization reversal process does not depend significantly on the relative sign of the effective magnetization in areas separated by domain walls.

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