Computational analysis of paramagnetic spherical Fe3O4 nanoparticles under permanent magnetic fields

2018 ◽  
Vol 154 ◽  
pp. 464-471 ◽  
Author(s):  
E.G. Karvelas ◽  
T.E. Karakasidis ◽  
I.E. Sarris
2004 ◽  
Vol 266 (4) ◽  
pp. 500-504 ◽  
Author(s):  
Jun Wang ◽  
Kai Zhang ◽  
Zhenmeng Peng ◽  
Qianwang Chen

Author(s):  
С.А. Борисов ◽  
А.А. Набережнов ◽  
B. Nacke ◽  
A. Nikanorov

The magnetic properties of two-phase borosilicate glasses containing in the skeleton a mixture of β-Fe2O3 and Fe3O4 nanoparticles have been studied. The sizes of nanoparticles have been determined, the value of blocking temperature (TB ~ 330 K) for ensemble of superparamagnetic nanoparticles is obtained. It is shown that in the high applied magnetic fields the specific magnetization of these glasses increases sharply at approaching and below Neel temperature for the bulk β-Fe2O3.


2020 ◽  
Vol 86 (2) ◽  
pp. 78-96
Author(s):  
Volodimir Grebennikov ◽  
Evgen Leonenko ◽  
Petro Manorik ◽  
Natalia Romanovska ◽  
Natalia Kobylinska ◽  
...  

The effect of superparamagnetic Fe3O4 nanoparticles (NPs) on the spectral luminescence properties of homogeneous optically transparent mesostructured silica films of SiO2/P123/Rh6G/Fe3O4, containing {P123 (Rh6G)} micelles consisting of Pluronic 123 with encapsulated Rh6G, and formed in stationary magnetic fields (MF) with an induction of less than 500 mT, was investigated. It was shown that, unlike SiO2/P123/Rh6G, the spectral and luminescent properties of SiO2/P123/Rh6G/Fe3O4 films depend on the MF used during their formation, and a gradual decrease in the band intensities in Rh6G spectra and quenching of luminescence with increasing of MF induction was observed. It is associated with a decrease in the monomer fraction and an increase in the fraction of non-luminescent Rh6G H-aggregates in micelles due to the interaction intensifying in the MF (formation of Fe3+ -O bonds) of superparamagnetic NPs with micelles {P123 (Rh6G)}, oriented in the MF, which leads to a gradual deformation of micelles and accumulation in them of H-aggregate. The dependences of the changes in the absorption bands intensity and fluorescence of the monomeric form of Rh6G in the spectra of the films on the changes in the magnetic induction of the MF are described by an exponential function, and the ratio of the fluorescence intensities of the SiO2/P123/Rh6G films to the fluorescence intensities of the SiO2/P123/Rh6G/Fe3O4 films linearly depends on the induction of MF, which they are able to "remember", which is manifested in the values of fluorescence intensities.


1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.


1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.


2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath

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.


2000 ◽  
Vol 179 ◽  
pp. 177-183
Author(s):  
D. M. Rust

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.


1977 ◽  
Vol 36 ◽  
pp. 191-215
Author(s):  
G.B. Rybicki

Observations of the shapes and intensities of spectral lines provide a bounty of information about the outer layers of the sun. In order to utilize this information, however, one is faced with a seemingly monumental task. The sun’s chromosphere and corona are extremely complex, and the underlying physical phenomena are far from being understood. Velocity fields, magnetic fields, Inhomogeneous structure, hydromagnetic phenomena – these are some of the complications that must be faced. Other uncertainties involve the atomic physics upon which all of the deductions depend.


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