Lorentz electron microscopy of rare-earth permanent magnets

1983 ◽  
Vol 41 ◽  
pp. 254-255
Author(s):  
G. C. Hadjipanayis ◽  
L. L. Horton
Keyword(s):  
Electron Microscopy ◽  
Rare Earth ◽  
Permanent Magnets ◽  
Domain Walls ◽  
Defect Density ◽  
Hexagonal Phase ◽  
Magnetic Hysteresis ◽  
Magnetic Domain ◽  
Pole Piece ◽  
Two Phase

Rare-earth-cobalt permanent magnets are characterized by large coercive fields and energy products. The hard magnetic properties depend strongly on the microstructure and are usually achieved after a complex heat treatment. A single phase microstructure with low defect density has been observed in SmCo5 and Sm2Co17 magnets. The addition of copper to these materials produces a two-phase cellular structure with a 1:5 hexagonal phase at the cell boundaries and a 2:17 rhombohedral phase in the cell interiors. The single- and two-phase microstructures lead to different magnetic hysteresis behavior. The purpose of this work is to determine the relationship of the microstructure with the magnetic domain structure to further clarify the origin of the high-coercive fields in these permanent magnet materials. Lorentz electron microscopy has been used to image the domain walls and study their interactions with crystalline defects. A JEM 120C TEM equipped with an AMG objective pole piece has been used for these studies. The magnetic field at the specimen is 3.4 Oe with this pole piece.

scholarly journals Mn-Induced Thermal Stability of L10 Phase in Fept Magnetic Nanoscale Ribbons

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1278
Author(s):  
Alina Daniela Crisan ◽  
Aurel Leca ◽  
Dan Pantelica ◽  
Ioan Dan ◽  
Ovidiu Crisan
Keyword(s):  
Rare Earth ◽  
Single Phase ◽  
Permanent Magnets ◽  
Magnetic Hysteresis ◽  
Ternary Alloys ◽  
Large Temperature ◽  
Nominal Composition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Operation Conditions

Magnetic nanoscale materials exhibiting the L10 tetragonal phase such as FePt or ternary alloys derived from FePt show most promising magnetic properties as a novel class of rare earth free permanent magnets with high operating temperature. A granular alloy derived from binary FePt with low Pt content and the addition of Mn with the nominal composition Fe57Mn8Pt35 has been synthesized in the shape of melt-spun ribbons and subsequently annealed at 600 °C and 700 °C for promoting the formation of single phase, L10 tetragonal, hard magnetic phase. Proton-induced X-ray emission spectroscopy PIXE has been utilized for checking the compositional effect of Mn addition. Structural properties were analyzed using X-ray diffraction and diffractograms were analyzed using full profile Rietveld-type analysis with MAUD (Materials Analysis Using Diffraction) software. By using temperature-dependent synchrotron X-ray diffraction, the disorder–order phase transformation and the stability of the hard magnetic L10 phase were monitored over a large temperature range (50–800 °C). A large interval of structural stability of the L10 phase was observed and this stability was interpreted in terms of higher ordering of the L10 phase promoted by the Mn addition. It was moreover found that both crystal growth and unit cell expansion are inhibited, up to the highest temperature investigated (800 °C), proving thus that the Mn addition stabilizes the formed L10 structure further. Magnetic hysteresis loops confirmed structural data, revealing a strong coercive field for a sample wherein single phase, hard, magnetic tetragonal L10 exists. These findings open good perspectives for use as nanocomposite, rare earth free magnets, working in extreme operation conditions.

scholarly journals Harmonic analysis and modelling of magnetisation process in soft ferromagnetic material

2017 ◽  
Vol 30 (1) ◽  
pp. 121-136
Author(s):  
Branko Koprivica ◽  
Ioan Dumitru ◽  
Alenka Milovanovic ◽  
Ovidiu Caltun
Keyword(s):  
Magnetic Field ◽  
Hysteresis Loop ◽  
Magnetic Induction ◽  
Domain Walls ◽  
Magnetic Hysteresis ◽  
Magnetic Domain ◽  
Fast Fourier Transformation ◽  
Induced Voltage ◽  
Harmonic Content ◽  
Excitation Magnetic Field

The aim of this paper is to present a research of magnetic hysteresis loops of a toroidal ferromagnetic core made of electrical steel. The experimental results of induced voltage, magnetic induction and hysteresis loop obtained at different frequencies of the sinusoidal excitation magnetic field have been presented. The harmonic content of the induced voltage and magnetic induction have been calculated using Fast Fourier Transformation. Observed variation of higher harmonics with frequency has been correlated to the mechanism of magnetic domain walls damping. A variation of harmonics of the magnetic induction with the amplitude of the excitation magnetic field has been analysed and a proper mathematical model has been proposed. Furthermore, the influence of the triangularly shaped excitation magnetic field and the distorted shape excitation that produces sinusoidal induction on the shape of hysteresis loop and harmonic content of the induced voltage and the magnetic induction has been analysed and discussed.

scholarly journals Extreme anti-reflection enhanced magneto-optic Kerr effect microscopy

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Dongha Kim ◽  
Young-Wan Oh ◽  
Jong Uk Kim ◽  
Soogil Lee ◽  
Arthur Baucour ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Kerr Effect ◽  
Domain Walls ◽  
State Of The Art ◽  
Magnetic Domain ◽  
Diffraction Limit ◽  
Scanning Probe ◽  
Spintronic Devices ◽  
Sub Wavelength ◽  
Magneto Optic

AbstractMagnetic and spintronic media have offered fundamental scientific subjects and technological applications. Magneto-optic Kerr effect (MOKE) microscopy provides the most accessible platform to study the dynamics of spins, magnetic quasi-particles, and domain walls. However, in the research of nanoscale spin textures and state-of-the-art spintronic devices, optical techniques are generally restricted by the extremely weak magneto-optical activity and diffraction limit. Highly sophisticated, expensive electron microscopy and scanning probe methods thus have come to the forefront. Here, we show that extreme anti-reflection (EAR) dramatically improves the performance and functionality of MOKE microscopy. For 1-nm-thin Co film, we demonstrate a Kerr amplitude as large as 20° and magnetic domain imaging visibility of 0.47. Especially, EAR-enhanced MOKE microscopy enables real-time detection and statistical analysis of sub-wavelength magnetic domain reversals. Furthermore, we exploit enhanced magneto-optic birefringence and demonstrate analyser-free MOKE microscopy. The EAR technique is promising for optical investigations and applications of nanomagnetic systems.

Magnetic domain-wall induced ferroelectric polarization in rare-earth orthoferrites AFeO3 (A = Lu, Y, Gd): first-principles calculations

2019 ◽  
Vol 7 (32) ◽  
pp. 10059-10065 ◽  
Author(s):  
Wenxuan Wang ◽  
Wei Sun ◽  
Guangbiao Zhang ◽  
Zhenxiang Cheng ◽  
Yuanxu Wang
Keyword(s):  
Rare Earth ◽  
First Principles ◽  
Ionic Radius ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Ferroelectric Polarization ◽  
First Principles Calculations ◽  
Magnetic Domain Wall ◽  
Magnetic Domain Walls ◽  
A Site

The spin-induced ferroelectric polarization at magnetic domain walls is dependent on the A-site ionic radius of AFeO3.

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.

scholarly journals On the YFe11Mo intermetallic characterization

2013 ◽  
Vol 19 (S4) ◽  
pp. 135-136
Author(s):  
D. Nunes ◽  
A.P. Gonçalves ◽  
J.Th.M. De Hosson ◽  
P.A. Carvalho
Keyword(s):  
Permanent Magnets ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Eutectic Mixture ◽  
Dendritic Morphology ◽  
Type Structure ◽  
Processing Route ◽  
Objective Lens ◽  
X Ray ◽  
Lorentz Microscopy

Rare-earth intermetallic compounds adopting the tetragonal ThMn12–type structure and containing high Fe concentrations have attracted considerable attention in the field of permanent magnets. Among them, the Y-Fe-Mo series has been extensively investigated, especially by X-ray diffraction (XRD), but the microstructural characterization was very limited.In the present work, Y:11Fe:Mo has been prepared by melting Y, Fe and Mo in an arc furnace followed by splat-quenching and/or annealing treatments. The structure, chemistry and magnetic domain configurations of the resulting polycrystalline aggregates have been investigated by XRD, scanning and transmission electron microscopies (SEM and TEM, respectively), energy dispersive X-ray spectroscopy (EDS) and Lorentz microscopy.A special emphasis was given to Lorentz microscopy, where contrast is based on the Lorentz deflection imposed on electrons by the passage through a magnetic specimen. The magnetic domains have been imaged by the intermediate lens in Fresnel mode, with the objective lens switched off. In these conditions the intermediate lens is defocused so that out-of-focus images of the specimen are formed: the magnetic domain walls are imaged as alternate bright (convergent) and dark (divergent) lines. For the overfocused image, bright lines occur at the position of domain walls for which the magnetisation on either side is deflecting the electrons towards the wall, whereas dark lines are observed at the walls for which the magnetisation on either side is deflecting the electrons away from the wall. The opposite contrast is observed at the underfocused image.The results have shown that the tetragonal YFe11-xMoy phase is predominant, with a cellular dendritic morphology (Figure 1), but a considerable presence of -Fe(Mo) could be inferred, forming a coarse intercellular eutectic mixture. Significant Fe segregation occurred during annealing. However, this composition variation corresponded to an extremely limited evolution of the lattice parameters, the Rietveld analysis pointing to Fe vacancies at the 8i sites on the annealed material. XRD and EDS results indicate that the fraction of point defects in the ThMn12-type structure adapts to the processing route and that the stable configuration depends on the temperature. The current study also showed that grain boundaries are usually associated with domain walls and that YFe11Mo grains present internal domain walls forming stripe/maze patterns characteristic of high anisotropy materials (Figure 2), while residual -Fe(Mo) grains exhibit vortex configurations (see arrows in Figures 2 (a-c)).The work was supported by the Portuguese Science Foundation through the CTM/48617/2002 and PEst-OE/CTM-UI0084/2011 grants.

scholarly journals Nanomagnetic properties of the meteorite cloudy zone

2018 ◽  
Vol 115 (49) ◽  
pp. E11436-E11445 ◽  
Author(s):  
Joshua F. Einsle ◽  
Alexander S. Eggeman ◽  
Ben H. Martineau ◽  
Zineb Saghi ◽  
Sean M. Collins ◽  
...  
Keyword(s):  
Rare Earth ◽  
Permanent Magnets ◽  
Electron Tomography ◽  
Magnetic Domain ◽  
Atom Probe ◽  
Parent Body ◽  
Slow Cooling ◽  
Micromagnetic Simulations ◽  
Resolution Electron ◽  
Potential Applications

Meteorites contain a record of their thermal and magnetic history, written in the intergrowths of iron-rich and nickel-rich phases that formed during slow cooling. Of intense interest from a magnetic perspective is the “cloudy zone,” a nanoscale intergrowth containing tetrataenite—a naturally occurring hard ferromagnetic mineral that has potential applications as a sustainable alternative to rare-earth permanent magnets. Here we use a combination of high-resolution electron diffraction, electron tomography, atom probe tomography (APT), and micromagnetic simulations to reveal the 3D architecture of the cloudy zone with subnanometer spatial resolution and model the mechanism of remanence acquisition during slow cooling on the meteorite parent body. Isolated islands of tetrataenite are embedded in a matrix of an ordered superstructure. The islands are arranged in clusters of three crystallographic variants, which control how magnetic information is encoded into the nanostructure. The cloudy zone acquires paleomagnetic remanence via a sequence of magnetic domain state transformations (vortex to two domain to single domain), driven by Fe–Ni ordering at 320 °C. Rather than remanence being recorded at different times at different positions throughout the cloudy zone, each subregion of the cloudy zone records a coherent snapshot of the magnetic field that was present at 320 °C. Only the coarse and intermediate regions of the cloudy zone are found to be suitable for paleomagnetic applications. The fine regions, on the other hand, have properties similar to those of rare-earth permanent magnets, providing potential routes to synthetic tetrataenite-based magnetic materials.

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