Impact of magnetic domains on magnetic flux concentrators

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

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Large-scale Motion of Solar Filaments

International Astronomical Union Colloquium ◽

10.1017/s0252921100064502 ◽

2000 ◽

Vol 179 ◽

pp. 205-208

Author(s):

Pavel Ambrož ◽

Alfred Schroll

Keyword(s):

Magnetic Flux ◽

Proper Motion ◽

Time Scale ◽

Large Scale ◽

Accuracy Of Measurements ◽

Solar Filaments ◽

General Movement ◽

Scale Motion ◽

Velocity Scatter

AbstractPrecise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.

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Solar Filaments as Tracers of Subsurface Processes

International Astronomical Union Colloquium ◽

10.1017/s0252921100064459 ◽

2000 ◽

Vol 179 ◽

pp. 177-183

Author(s):

D. M. Rust

Keyword(s):

Magnetic Fields ◽

Magnetic Flux ◽

Coronal Mass Ejections ◽

Interplanetary Space ◽

Intermediate Stage ◽

Coronal Plasma ◽

Magnetic Helicity ◽

The Sun ◽

New Paradigm ◽

Solar Filaments

AbstractSolar filaments are discussed in terms of two contrasting paradigms. The standard paradigm is that filaments are formed by condensation of coronal plasma into magnetic fields that are twisted or dimpled as a consequence of motions of the fields’ sources in the photosphere. According to a new paradigm, filaments form in rising, twisted flux ropes and are a necessary intermediate stage in the transfer to interplanetary space of dynamo-generated magnetic flux. It is argued that the accumulation of magnetic helicity in filaments and their coronal surroundings leads to filament eruptions and coronal mass ejections. These ejections relieve the Sun of the flux generated by the dynamo and make way for the flux of the next cycle.

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Sunspot Groups as Tracers of Sub-Surface Processes

International Astronomical Union Colloquium ◽

10.1017/s0252921100064393 ◽

2000 ◽

Vol 179 ◽

pp. 155-160

Author(s):

M. H. Gokhale

Keyword(s):

Magnetic Flux ◽

Indian Institute ◽

Surface Processes ◽

The Sun ◽

Global And Local ◽

Sunspot Groups

AbstractData on sunspot groups have been quite useful for obtaining clues to several processes on global and local scales within the sun which lead to emergence of toroidal magnetic flux above the sun’s surface. I present here a report on such studies carried out at Indian Institute of Astrophysics during the last decade or so.

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Development of 200 kV Scanning-Transmission Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052067 ◽

1974 ◽

Vol 32 ◽

pp. 410-411

Author(s):

H. Koike ◽

S. Sakurai ◽

K. Ueno ◽

M. Watanabe

Keyword(s):

Electron Microscopy ◽

Electron Microscope ◽

Scanning Transmission Electron Microscope ◽

The Other ◽

Morphological Observation ◽

Magnetic Domains ◽

Transmission Electron ◽

Scanning Transmission ◽

Backscattered Electron ◽

Increasing Demand

In recent years, there has been increasing demand for higher voltage SEMs, in the field of surface observation, especially that of magnetic domains, dislocations, and electron channeling patterns by backscattered electron microscopy. On the other hand, the resolution of the CTEM has now reached 1 ∼ 2Å, and several reports have recently been made on the observation of atom images, indicating that the ultimate goal of morphological observation has beem nearly achieved.

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

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109458 ◽

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.

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Magnetic Material Observation Assembly for Tem with a Eucentric Goniometer

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100092669 ◽

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.

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Lorentz electron microscopy of magnetic domains in rapidly solidified and annealed Pt-Co-B alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100088233 ◽

1991 ◽

Vol 49 ◽

pp. 784-785

Author(s):

N. Qiu ◽

J. E. Wittig

Keyword(s):

Rapid Solidification ◽

Ion Beam ◽

Magnetic Behavior ◽

High Coercivity ◽

Magnetic Domains ◽

Beam Angle ◽

Tem Analysis ◽

Intrinsic Coercivity ◽

Hard Magnets ◽

Rapidly Solidified

PtCo hard magnets have specialized applications owing to their relatively high coercivity combined with corrosion resistance and ductility. Increased intrinsic coercivity has been recently obtained by rapid solidification processing of PtCo alloys containing boron. After rapid solidification by double anvil splat quenching and subsequent annealing for 30 minutes at 650°C, an alloy with composition Pt42Co45B13 (at.%) exhibited intrinsic coercivity up to 14kOe. This represents a significant improvement compared to the average coercivities in conventional binary PtCo alloys of 5 to 8 kOe.Rapidly solidified specimens of Pt42Co45B13 (at.%) were annealed at 650°C and 800°C for 30 minutes. The magnetic behavior was characterized by measuring the coercive force (Hc). Samples for TEM analysis were mechanically thinned to 100 μm, dimpled to about 30 nm, and ion milled to electron transparency in a Gatan Duomill at 5 kV and 1 mA gun current. The incident ion beam angle was set at 15° and the samples were liquid nitrogen cooled during milling. These samples were analyzed with a Philips CM20T TEM/STEM operated at 200 kV.

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

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100098113 ◽

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.

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