scholarly journals Cálculo da constante de dureza em sistemas ferromagnéticos

1986 ◽  
Vol 8 (8) ◽  
pp. 07
Author(s):  
Ronaldo Mota
Keyword(s):  
Spin Wave ◽  
Exchange Coupling ◽  
Random Phase Approximation ◽  
Random Phase ◽  
Wide Band ◽  
Band Model ◽  
Dynamical Susceptibility ◽  
Stiffness Constant ◽  
Two Band Model ◽  
Narrow Bands

A two-band model for the magnetism is used to calculate the stiffness constant in ferromagnetic systems. One band is narrow and degenerated, representing the "quasi-localized" electrons. The second one is a wide band containing very few itinerant electrons. The transverse dynamical susceptibility is calculated within the random-phase approximation (RPA). The value of the stiffness constant of the acoustical spin wave is essential to satisfy the criterion of ferromagnetic stability at T = 0K. From the poles of the susceptibility two spin-wave branches are derived: one acoustic and one optic. It is shown that taking into account the interatomic exchange coupling between electrons of the narrow bands is necessary for the spin-wave stiffness constant to assume the experimental value.

SCREENED INTERACTION AND COULOMB PSEUDO-POTENTIAL IN C60

1992 ◽  
Vol 06 (23n24) ◽  
pp. 3993-4005 ◽  
Author(s):  
O. Gunnarsson ◽  
D. Rainer ◽  
G. Zwicknagl
Keyword(s):  
Random Phase Approximation ◽  
Traditional Approach ◽  
Random Phase ◽  
Substantial Reduction ◽  
Band Model ◽  
Coupling Constant ◽  
Electron Phonon Coupling ◽  
Pseudo Potential ◽  
Efficient Screening ◽  
Two Band Model

We study the screening for C 60 in the random phase approximation. For a free molecule we find a substantial reduction of the interaction between close atoms but an “antiscreening” of the interaction between distant atoms. For a C 60 solid there is an efficient screening of the intraband Coulomb interaction (U~0.05 eV ), leading to µ=UN(0)~0.4, where N(0) is the density of states per spin and molecule. We then study the renormalization of the Coulomb pseudo-potential µ* due to higher subbands in a simple two-band model. We find that the renormalization is small, although a traditional approach, summing ladder diagrams in the screened interaction, predicts a large renormalization. This suggests that µ* may not be much smaller than µ~0.4 in C 60. To obtain reasonable transition temperatures, Tc, this value of μ* (~0.4) requires values of the electron-phonon coupling constant λ, which are not very much larger than what has been calculated.

Spin‐Wave Theory of MnF2 in the Random Phase Approximation

1965 ◽  
Vol 36 (3) ◽  
pp. 1138-1140 ◽  
Author(s):  
H. R. Carleton ◽  
R. Brout ◽  
R. Stinchcombe
Keyword(s):  
Spin Wave ◽  
Random Phase Approximation ◽  
Random Phase ◽  
Wave Theory ◽  
Phase Approximation ◽  
Spin Wave Theory

scholarly journals Ferromagnetic Damping/Anti-damping in a Periodic 2D Helical Surface; A Nonequilibrium Keldysh Green Function Approach

SPIN ◽  
2016 ◽  
Vol 06 (02) ◽  
pp. 1640009 ◽  
Author(s):  
Farzad Mahfouzi ◽  
Nicholas Kioussis
Keyword(s):  
Electronic Transport ◽  
Surface State ◽  
Exchange Coupling ◽  
Band Model ◽  
Spin Orbit ◽  
Helical Surface ◽  
Gilbert Damping ◽  
Magnetization Precession ◽  
Green Function Approach ◽  
Two Band Model

In this paper, we investigate theoretically the spin–orbit torque (SOT) as well as the Gilbert damping for a two band model of a 2D helical surface state with a ferromagnetic (FM) exchange coupling. We decompose the density matrix into the Fermi sea and Fermi surface components and obtain their contributions to the electronic transport as well as the SOT. Furthermore, we obtain the expression for the Gilbert damping due to the surface state of a 3D topological insulator (TI) and predict its dependence on the direction of the magnetization precession axis.

SYNTHESIS OF Ru1-xSbxSr2(Eu0.7Ce0.3)2Cu2O10-δ AND THEIR MAGNETIC AND TRANSPORT PROPERTIES

2005 ◽  
Vol 19 (22) ◽  
pp. 3511-3517 ◽  
Author(s):  
T. R. YANG ◽  
G. ILONCA ◽  
F. BEIUŞAN ◽  
A. V. POP ◽  
V. TOMA ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Hall Effect ◽  
Exchange Coupling ◽  
Solid State Reaction Method ◽  
Band Model ◽  
X Ray Diffraction ◽  
Conventional Solid State Reaction ◽  
X Ray ◽  
Two Band Model ◽  
Hole Localization

Ru 1-x Sb x Sr 2( Eu 0.7 Ce 0.3)2 Cu 2 O 10-δ systems were prepared by conventional solid state reaction method. The structural analysis was investigated using X-ray diffraction. Electrical resistivity, Hall effect and magnetic susceptibility measurements on Ru :1222 doped with Sb are presented, together with results in the temperature range 5–300 K. Transition temperature decreases from 43 K for x = 0.00 to 20 K for x = 0.06 Sb . This may be due to a distortion of RuO 6 octahedral, which is responsible of the increase in hole localization. The Hall effect anomalous decreases below T magnetic which may be explained within a simple two-band model by a transition from localized to more itinerant behavior in the RuO 2 layer at T magnetic . The behavior of magnetic susceptibility is caused by an antisymmetric exchange coupling of the Dzyaloshinsky–Morya type between neighboring Ru moments.

RKKY theory of oscillatory exchange coupling in the generalized random-phase approximation

1999 ◽  
Vol 59 (22) ◽  
pp. 14461-14465 ◽  
Author(s):  
M. Noshiravani ◽  
A. Koohi ◽  
F. Ebrahimi ◽  
M. M. Tehranchi
Keyword(s):  
Exchange Coupling ◽  
Random Phase Approximation ◽  
Random Phase ◽  
Phase Approximation

Interpretation of Preferential Adsorption Using Random Phase Approximation Theory

1995 ◽  
Vol 60 (10) ◽  
pp. 1641-1652 ◽  
Author(s):  
Henri C. Benoît ◽  
Claude Strazielle
Keyword(s):  
Approximation Theory ◽  
Random Phase Approximation ◽  
Virial Coefficient ◽  
Random Phase ◽  
Second Virial Coefficient ◽  
Solvent Mixture ◽  
Gyration Radius ◽  
Thermodynamic Quantities ◽  
Phase Approximation ◽  
Preferential Adsorption

It has been shown that in light scattering experiments with polymers replacement of a solvent by a solvent mixture causes problems due to preferential adsorption of one of the solvents. The present paper extends this theory to be applicable to any angle of observation and any concentration by using the random phase approximation theory proposed by de Gennes. The corresponding formulas provide expressions for molecular weight, gyration radius, and the second virial coefficient, which enables measurements of these quantities provided enough information on molecular and thermodynamic quantities is available.

Neutrino reactions onC12by the quasiparticle random-phase approximation (QRPA)

2010 ◽  
Vol 81 (2) ◽  
Author(s):  
Myung-Ki Cheoun ◽  
Eunja Ha ◽  
Su Youn Lee ◽  
K. S. Kim ◽  
W. Y. So ◽  
...  
Keyword(s):  
Random Phase Approximation ◽  
Random Phase ◽  
Phase Approximation ◽  
Quasiparticle Random Phase Approximation
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