scholarly journals Remanence and Switching Sensitivity in Nanodot Magnetic Arrays

2008 ◽  
Vol 8 (6) ◽  
pp. 2897-2900
Author(s):  
Przemysław Gawrónski ◽  
Krzysztof Kułakowski
Keyword(s):  
Magnetic Field ◽  
Standard Deviation ◽  
Magnetic Behaviour ◽  
The Other ◽  
Square Lattice ◽  
Switching Field ◽  
Damage Spreading ◽  
Oscillating Magnetic Field ◽  
The Stability ◽  
Intermediate Value

New results are reported of the computer simulations on the magnetic behaviour of magnetic arrays of nanoscopic dots, placed in cells of the square lattice. We show that the remanence magnetization Mr decreases with the array size. For arrays 50 × 50, we investigate also the stability of the magnetic structure of an array in an oscillating magnetic field. The damage spreading technique reveals that this stability increases with the standard deviation σ of the switching field of individual elements of the array. On the other hand, Mr decreases with σ. An optimalization of the system (large Mr and large stability) can then be reached at some intermediate value of σ.

scholarly journals General Discussion of Accretion Disks

1999 ◽  
Vol 194 ◽  
pp. 321-322
Author(s):  
Vahagn G. Gurzadyan
Keyword(s):  
Magnetic Field ◽  
Accretion Disks ◽  
Galactic Nuclei ◽  
The Other ◽  
Seminal Paper ◽  
Physical Conditions ◽  
Electron Positron ◽  
Free Parameters ◽  
The Stability ◽  
Electron Positron Pair

Even 25 years after the Shakura-Sunyaev seminal paper on the α-disk, we cannot claim that we have a reliable theory of accretion disks in galactic nuclei. Why? Because the problem is extremely complicated, it is essentially nonlinear and contains a number of parameters (i.e. is many-dimensional). The key point is whether it is possible to determine the magneto-hydrodynamical viscosity self-consistently, i.e. as a function of parameters of the disk - the temperature, matter and radiation densities, magnetic field, radius, etc., both in the radiation dominated and matter dominated regions. Another class of fundamental problems concerns the stability of the disk; Krolik mentioned only one instability - in the radiation dominated region, but there are many other types of instabilities which are quite sensitive to the physical conditions in the disk, for example, to the anisotropy of the ion pressure in the outer regions and possible electron-positron pair production near the inner edge of the disk. The other problems include those of the radiative transfer within the disk in various conditions, Comptonization of the outgoing radiation, radiation reflections by the desk, etc. Therefore it is not suprising that one can ‘explain' almost whatever he wants - spectra, variability, jets, wind, etc., by proper fit of the ‘free’ (which are never free) parameters and ignoring the instabilities and so on.

scholarly journals Magnetotellurics with a remote magnetic reference

Geophysics ◽  
1979 ◽  
Vol 44 (1) ◽  
pp. 53-68 ◽  
Author(s):  
T. D. Gamble ◽  
W. M. Goubau ◽  
J. Clarke
Keyword(s):  
Magnetic Field ◽  
Standard Deviation ◽  
Magnetic Fields ◽  
Apparent Resistivity ◽  
The Other ◽  
Impedance Tensor ◽  
Free Data ◽  
Electric And Magnetic Fields ◽  
Conventional Methods ◽  
The Magnetic Field

Magnetotelluric measurements were performed simultaneously at two sites 4.8 km apart near Hollister, California. SQUID magnetometers were used to measure fluctuations in two orthogonal horizontal components of the magnetic field. The data obtained at each site were analyzed using the magnetic fields at the other site as a remote reference. In this technique, one multiplies the equations relating the Fourier components of the electric and magnetic fields by a component of magnetic field from the remote reference. By averaging the various crossproducts, estimates of the impedance tensor not biased by noise are obtained, provided there are no correlations between the noises in the remote channels and noises in the local channels. For some data, conventional methods of analysis yielded estimates of apparent resistivities that were biased by noise by as much as two orders of magnitude. Nevertheless, estimates of the apparent resistivity obtained from these same data, using the remote reference technique, were consistent with apparent resistivities calculated from relatively noise‐free data at adjacent periods. The estimated standard deviation for periods shorter than 3 sec was less than 5 percent, and for 87 percent of the data, was less than 2 percent. Where data bands overlapped between periods of 0.33 sec and 1 sec, the average discrepancy between the apparent resistivities was 1.8 percent.

scholarly journals Prominence Oscillations and the Influence of the Distant Photosphere

1998 ◽  
Vol 167 ◽  
pp. 147-150
Author(s):  
N.A.J. Schutgens ◽  
M. Kuperus ◽  
G.H.J. van den Oord
Keyword(s):  
Magnetic Field ◽  
Boundary Condition ◽  
The Other ◽  
Forced Oscillations ◽  
Crossing Time ◽  
Self Consistent ◽  
Normal Polarity ◽  
The Stability ◽  
The Magnetic Field ◽  
Flux Conservation

AbstractWe model vertical prominence dynamics, describing the evolution of the magnetic field in a self-consistent way. Since the photosphere imposes a boundary condition on the field (flux conservation), the Alfvén crossing time τ0/2 between prominence and photosphere has to be taken into account. Using an electrodynamical description of the prominence we are able to compare two basic prominence models: Normal Polarity (NP) and Inverse Polarity (IP).The results indicate that for IP prominences, the stability properties are sensitive to ωτ0 (ω: oscillation frequency of prominence). For ωτ0 ≳ 1 instability results. Forced oscillations of five minutes are efficiently excited in IP prominences that meet certain criteria only. NP prominences on the other hand, are insensitive to the Alfvén crossing time. Forced oscillations of five minutes are difficult to excite in NP prominences.

Stability of a stratified partially ionized plasma in a vertical magnetic field

1978 ◽  
Vol 19 (1) ◽  
pp. 183-191 ◽  
Author(s):  
S. L. Maheshwari ◽  
P. K. Bhatia
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Growth Rate ◽  
The Other ◽  
Conducting System ◽  
Vertical Magnetic Field ◽  
One Dimensional ◽  
Finite Electrical Conductivity ◽  
Partially Ionized ◽  
The Stability

The dynamic stability of a stratified layer of partially ionized compressible plasma is discussed to investigate the effects of finite electrical conductivity and ion viscosity. The prevailing magnetic field is assumed to be uniform and vertical. For a semi-infinite plasma having a one-dimensional exponential density gradient along the vertical, the dispersion relation has been obtained by variational methods. It is found that the ion viscosity and ion–neutral collisions, whether included jointly or separately, do not change the stability criterion of the perfectly conducting system. Their inclusion, however, has a tendency to reduce the growth rate of the unstable perturbations showing that they have a stabilizing influence. On the other hand the inclusion of the effects of finite resistivity and compressibility of the medium is found to be destabilizing as the wavenumber range over which the plasma would otherwise be stable, becomes unstable.

Light Scattering from Magnetic Latex Particles

1991 ◽  
Vol 248 ◽  
Author(s):  
Daewon Sohn ◽  
L. M. DeLong ◽  
Paul S. Russo
Keyword(s):  
Magnetic Field ◽  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Physical Model ◽  
The Other ◽  
Sodium Polystyrene Sulfonate ◽  
Polystyrene Sulfonate ◽  
Simple Physical Model ◽  
Plastic Sphere ◽  
Oscillating Magnetic Field

AbstractTwo magnetic latex preparations have been measured by polarized and depolarized dynamic light scattering. The adherence of the latexes to a simple physical model, that of a bar magnet embedded in a plastic sphere, is judged adequate in one case, but not the other. Preliminary efforts to use the latex spheres as probes of sodium polystyrene sulfonate solutions are described. A few observations are made concerning the dynamic light scattering behavior of the magnetic latex under the influence of an externally applied, oscillating magnetic field.

Some magnetic properties of metals. V. Magnetic behaviour of a cylindrical system of electrons for all magnetic fields

1953 ◽  
Vol 216 (1124) ◽  
pp. 118-142 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Properties ◽  
Wave Function ◽  
Magnetic Susceptibility ◽  
Uniform Magnetic Field ◽  
Magnetic Behaviour ◽  
The Other ◽  
Cylindrical System ◽  
Different Types ◽  
Large Systems

The Wentzel-Kramers-Brillouin method is used to solve the Schrödinger equation for an electron moving in a uniform magnetic field H , the boundary of the system being a cylinder with its axis lying along the direction of the field. It is found that there are two entirely different types of wave-function possible, one type leading to the small Landau diamagnetism of large systems discussed in part I of this series, the other to the larger diamagnetism of small systems discussed in part IV. Taking into account the occupied states of both types, the steady (non-periodic) contributions to the magnetic susceptibility are derived for all fields in both the low- and high-temperature limits, and for most fields at intermediate temperatures.

Scattering of circularly polarized electromagnetic waves off a straight electron beam propagating along a constant magnetic field

1991 ◽  
Vol 46 (2) ◽  
pp. 201-207
Author(s):  
Alexander Bogdanov
Keyword(s):  
Magnetic Field ◽  
Nonlinear Dynamics ◽  
Electron Beam ◽  
Electromagnetic Waves ◽  
Electron Beams ◽  
The Other ◽  
Free Electron Lasers ◽  
Circularly Polarized ◽  
Beam Density ◽  
The Stability

The stability of straight field-aligned electron beams, immersed in an external magnetic field of finite magnitude, with respect to the excitation in them of circularly polarized (spiral) electromagnetic waves is a problem calling for detailed investigation, particularly in the context of the study and development of free-electron lasers. Traditionally the problem is treated using the theory of electromagnetic waves scattering off electron-beam density oscillations. This is done, however, without considering the inverse influence of the beam on the dispersion properties of the electromagnetic waves. On the other hand, it is well known that the presence of the beam introduces substantial changes in the characteristics of the electromagnetic waves interacting with the beam, and, moreover, this results in the appearance of radically new types of waves that are entirely absent in free space. The paper is dedicated to the study of the nonlinear dynamics of the interaction of such radically changed electromagnetic waves with the beam density oscillations.

Dynamic hysteresis and compensation behaviors of the bilayer Blume–Capel model under an oscillating magnetic field

2019 ◽  
Vol 33 (30) ◽  
pp. 1950369 ◽  
Author(s):  
Mehmet Bati
Keyword(s):  
Magnetic Field ◽  
Crystal Field ◽  
Mean Field ◽  
Field Approximation ◽  
Square Lattice ◽  
Mean Field Approximation ◽  
Dynamic Compensation ◽  
Compensation Behavior ◽  
Oscillating Magnetic Field ◽  
Hysteresis Characteristics

Dynamic compensation and hysteresis characteristics of Blume–Capel (BC) model under an oscillating magnetic field have been studied within the dynamic mean field approximation. Spin-1 ferro-antiferromagnetic system Hamiltonian contains bilinear and crystal-field interactions in the presence of a time-dependent oscillating external magnetic field on a bilayer square lattice. Benefiting from the thermal variations of the total magnetization, we find the L-, Q-, R- and S-type compensation behaviors in the system. According to our results, the system does not represent dynamic compensation behavior when it only includes one interaction parameter. We found that the existence of compensation temperatures and hysteresis properties strongly depends on crystal field interactions. It has also been shown that for the paramagnetic phase of the system, single hysteresis behaviors may occur. Finally, the obtained results are compared with some experimental and theoretical results and found in a qualitatively good agreement.

scholarly journals REENTRANT BEHAVIOR IN LANDAU–FERMI LIQUIDS WITH SPIN-SPLIT POMERANCHUK INSTABILITIES

2012 ◽  
Vol 26 (19) ◽  
pp. 1250125 ◽  
Author(s):  
P. RODRÍGUEZ PONTE ◽  
D. C. CABRA ◽  
N. GRANDI
Keyword(s):  
Magnetic Field ◽  
Phase Space ◽  
Fermi Liquid ◽  
Chemical Potential ◽  
Square Lattice ◽  
Fermi Liquids ◽  
Lattice Systems ◽  
Fermi Surfaces ◽  
The Stability ◽  
The Magnetic Field

We study the effects of spin-antisymmetric interactions on the stability of a Landau–Fermi liquid on the square lattice, using the generalized Pomeranchuk method for two-dimensional lattice systems. In particular, we analyze interactions that could induce instabilities of the so-called spin-split type, that is when spin-up and spin-down Fermi surfaces are displaced with respect to each other. The phase space is studied as a function of the strength of the interaction V, the electron chemical potential μ and an external magnetic field h. We find that such interactions produce in general an enhancement of the instability region of the Landau–Fermi liquid. More interestingly, in certain regions of the V–μ phase space, we find a reentrant behavior as a function of the magnetic field h, similar to that found in recent experiments, e.g. in URu 2 Si 2 and Sr 3 Ru 2 O 7.

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