Electronic Structure and Magnetic Properties of Nd5Fe17

1999 ◽  
Vol 577 ◽  
Author(s):  
R. F. Sabiryanov ◽  
S. S. Jaswal
Keyword(s):  
Magnetic Properties ◽  
Electronic Structure ◽  
Curie Temperature ◽  
Magnetic Moments ◽  
Mean Field ◽  
Local Environment ◽  
Field Approximation ◽  
Experimental Result ◽  
Mean Field Approximation ◽  
Orbital Method

ABSTRACTThe Nd5Fel compound has attracted some attention lately as a possible permanent-magnet material. This compound has a very complicated crystal structure (264 atoms per unit cell with 14 and 7 different Fe and Nd sites respectively!) Using linear-muffin-tin-orbital method, self-consistent spin-polarized studies of NdFe1 - have been carried out to determine the electronic structure, magnetic moments, and the Curie temperature. The results show strong effect of the local environment on the magnetic properties of individual Fe sites. The calculated moments are compared with the magnetization data. The Curie temperature estimated for the iron sublattice using the mean-field approximation is in a reasonable agreement with the experimental result.

First Principles Study of the Phase Transitions of MnAs

2006 ◽  
Vol 941 ◽  
Author(s):  
Ivan Rungger ◽  
Stefano Sanvito
Keyword(s):  
Phase Transition ◽  
Curie Temperature ◽  
Cell Volume ◽  
Order Phase Transition ◽  
Structural Changes ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
First Order Phase Transition ◽  
The Stability

ABSTRACTThe magnetic and structural properties of MnAs are investigated by mapping ab initio total energies onto a Heisenberg Hamiltonian. We study the dependence of the Curie temperature over the unit cell volume and an orthorhombic distortion by using the mean field approximation, and find that for orthorhombically distorted cells the Curie temperature is much smaller than for hexagonal cells. We provide an explanation for the structural changes of both the first order phase transition at 318 K and the second order phase transition at 400 K, with the cell volume driving the stability of the different structures in the paramagnetic state. The stable cell is found to be orthorhombic up to a critical lattice constant of about 3.7 Å, above which it remains hexagonal.

scholarly journals Электронные и магнитные свойства сплавов DyFe-=SUB=-4-=/SUB=-Ge-=SUB=-2-=/SUB=- в области фазового перехода

2020 ◽  
Vol 62 (6) ◽  
pp. 823
Author(s):  
М.В. Матюнина ◽  
М.А. Загребин ◽  
В.В. Соколовский ◽  
В.Д. Бучельников
Keyword(s):  
Magnetic Properties ◽  
Mean Field ◽  
Magnetic Ordering ◽  
Exchange Interactions ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Local Spin Density Approximation ◽  
Electronic And Magnetic Properties ◽  
Strong Localization ◽  
The Mean

Abstract The first-principles studies have been performed for the electronic and magnetic properties of DyFe_4Ge_2 alloys near the P 4_2/ mmm – Cmmm phase transition. The calculations are carried out in a local spin density approximation taking into account the Coulomb interaction within the limit of strong localization in a mean field approximation. The electronic and magnetic properties of the tetragonal structure are shown to be weakly changed in the dependence on the Coulomb and exchange interactions and also on the choice of the approximations. In the case of the orthorhombic structure, a change in the parameters of the Coulomb and exchange interactions leads to a change in the magnetic ordering: from the ferromagnetic to ferrimagnetic in the strong localization limit and from the ferromagnetic to paramagnetic in the mean field approximation.

Phase Transitions and the Ising Model

2019 ◽  
pp. 423-446
Author(s):  
Robert H. Swendsen
Keyword(s):  
Phase Transitions ◽  
Ising Model ◽  
Landau Theory ◽  
Magnetic Moments ◽  
Mean Field ◽  
Higher Dimensions ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Ising Chain ◽  
The Mean

Chapter 17 presented one example of a phase transition, the van der Waals gas. This chapter provides another, the Ising model, a widely studied model of phase transitions. We first give the solution for the Ising chain (one-dimensional model), including the introduction of the transfer matrix method. Higher dimensions are treated in the Mean Field Approximation (MFA), which is also extended to Landau theory. The Ising model is deceptively simple. It can be defined in a few words, but it displays astonishingly rich behavior. It originated as a model of ferromagnetism in which the magnetic moments were localized on lattice sites and had only two allowed values.

Influence of Surface Magnetism on the Surface Segregation Near TC in NiX Cu1-x Alloys

1983 ◽  
Vol 21 ◽  
Author(s):  
J. Urias ◽  
J.L. Moran-Lopez
Keyword(s):  
Magnetic Moment ◽  
Surface Segregation ◽  
Mean Field ◽  
Local Environment ◽  
Local Magnetic Moment ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Surface Magnetism ◽  
Surface Magnetization ◽  
The Mean

ABSTRACTThe influence of surface magnetization on the surface segregation in binary alloys with one magnetic component is studied. Based in a model in which the local magnetic moment on the ferromagnetic atoms is determined by the local environment, the internal energy is calculated within the mean field approximation. We applied the model to dilute CuNi alloys and we find that magnetism favors the segregation of Ni, contrary to what it is found in the paramagnetic phase.

scholarly journals Collective in-plane magnetization in a two-dimensional XY macrospin system within the framework of generalized Ott–Antonsen theory

2020 ◽  
Vol 378 (2171) ◽  
pp. 20190259 ◽  
Author(s):  
Irina V. Tyulkina ◽  
Denis S. Goldobin ◽  
Lyudmila S. Klimenko ◽  
Igor S. Poperechny ◽  
Yuriy L. Raikher
Keyword(s):  
Magnetic Moments ◽  
Mean Field ◽  
Ferromagnetic State ◽  
Dipole Interaction ◽  
Field Approximation ◽  
Square Lattice ◽  
Mean Field Approximation ◽  
Two Dimensional ◽  
Stripe Structure ◽  
First Order Phase

The problem of magnetic transitions between the low-temperature (macrospin ordered) phases in two-dimensional XY arrays is addressed. The system is modelled as a plane structure of identical single-domain particles arranged in a square lattice and coupled by the magnetic dipole–dipole interaction; all the particles possess a strong easy-plane magnetic anisotropy. The basic state of the system in the considered temperature range is an antiferromagnetic (AF) stripe structure, where the macrospins (particle magnetic moments) are still involved in thermofluctuational motion: the superparamagnetic blocking T b temperature is lower than that ( T af ) of the AF transition. The description is based on the stochastic equations governing the dynamics of individual magnetic moments, where the interparticle interaction is added in the mean-field approximation. With the technique of a generalized Ott–Antonsen theory, the dynamics equations for the order parameters (including the macroscopic magnetization and the AF order parameter) and the partition function of the system are rigorously obtained and analysed. We show that inside the temperature interval of existence of the AF phase, a static external field tilted to the plane of the array is able to induce first-order phase transitions from AF to ferromagnetic state; the phase diagrams displaying stable and metastable regions of the system are presented. This article is part of the theme issue ‘Patterns in soft and biological matters’.

Magnetism and magnetic anisotropy in UGa2

MRS Advances ◽  
2020 ◽  
Vol 5 (51) ◽  
pp. 2639-2645
Author(s):  
Banhi Chatterjee ◽  
Jindřich Kolorenč
Keyword(s):  
Density Functional ◽  
Magnetocrystalline Anisotropy ◽  
Magnetic Moments ◽  
Mean Field ◽  
Field Approximation ◽  
Theoretical Description ◽  
Mean Field Approximation ◽  
Functional Theory ◽  
Hubbard Interaction ◽  
The Density Functional Theory

AbstractWe investigate whether first-principles calculations with an improved description of electronic correlations can explain the large magnetic moments and the strong magnetocrystalline anisotropy in the ferromagnetic compound UGa2. The correlations are treated within a static mean-field approximation DFT+U combining the density functional theory (DFT) with an onsite Hubbard interaction U. We find that DFT+U improves the agreement of the magnetic moments with the experiment compared to DFT but worsens the theoretical description of the magnetocrystalline anisotropy.

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