Noncollinear spin-fluctuation theory of transition-metal magnetism: Role of transverse spin fluctuations in Fe

2015 ◽  
Vol 91 (18) ◽  
Author(s):  
R. Garibay-Alonso ◽  
J. Dorantes-Dávila ◽  
G. M. Pastor
Keyword(s):  
Transition Metal ◽  
Spin Fluctuation ◽  
Spin Fluctuations ◽  
Fluctuation Theory ◽  
Transverse Spin

Extended Dynamic Spin-Fluctuation Theory with Application to Iron

2012 ◽  
Vol 190 ◽  
pp. 55-58 ◽  
Author(s):  
B.I. Reser ◽  
N.B. Melnikov ◽  
Vladimir I. Grebennikov
Keyword(s):  
Phase Transition ◽  
Magnetic Properties ◽  
Green Function ◽  
Spin Fluctuation ◽  
Spin Fluctuations ◽  
Fluctuation Theory ◽  
Dynamic Spin ◽  
Discontinuous Phase ◽  
The Mean ◽  
Extended Dynamic

The problem of discontinuous phase transition in the dynamic spin-fluctuation theory is resolved by taking into account large anharmonic spin fluctuations and nonlocality of the mean Green function. The extended theory is applied to the calculation of magnetic properties of iron.

scholarly journals The Characteristic Properties of Magnetostriction and Magneto-Volume Effects of Ni2MnGa-Type Ferromagnetic Heusler Alloys

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3655 ◽  
Author(s):  
Sakon ◽  
Yamasaki ◽  
Kodama ◽  
Kanomata ◽  
Nojiri ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Spin Fluctuation ◽  
Heusler Alloys ◽  
Spin Fluctuations ◽  
Fluctuation Theory ◽  
Itinerant Electron ◽  
Valence Electron Concentration ◽  
Lattice Softening ◽  
The Magnetic Field ◽  
Volume Effects

In this article, we review the magnetostriction and magneto-volume effects of Ni2MnGa-type ferromagnetic Heusler alloys at the martensitic, premartensitic, and austenitic phases. The correlations of forced magnetostriction (ΔV/V) and magnetization (M), using the self-consistent renormalization (SCR) spin fluctuation theory of an itinerant electron ferromagnet proposed by Takahashi, are evaluated for the ferromagnetic Heusler alloys. The magneto-volume effect occurs due to the interaction between the magnetism and volume change of the magnetic crystals. The magnetic field-induced strain (referred to as forced magnetostriction) and the magnetization are measured, and the correlation of magnetostriction and magnetization is evaluated. The forced volume magnetostriction ΔV/V at the Curie temperature, TC is proportional to M4, and the plots cross the origin point; that is, (M4, ΔV/V) = (0, 0). This consequence is in good agreement with the spin fluctuation theory of Takahashi. An experimental study is carried out and the results of the measurement agree with the theory. The value of forced magnetostriction is proportional to the valence electron concentration per atom (e/a). Therefore, the forced magnetostriction reflects the electronic states of the ferromagnetic alloys. The magnetostriction near the premartensitic transition temperature (TP) induces lattice softening; however, lattice softening is negligible at TC. The forced magnetostriction at TC occurs due to spin fluctuations of the itinerant electrons. In the martensitic and premartensitic phases, softening of the lattice occurs due to the shallow hollow (potential barrier) of the total energy difference between the L21 cubic and modulated 10M or 14M structures. As a result, magnetostriction is increased by the magnetic field.

ANOMALIES IN SPECIFIC HEAT: THE INFLUENCE OF SPIN FLUCTUATIONS AND SUPERCONDUCTIVITY IN CUPRATES

2013 ◽  
Vol 27 (13) ◽  
pp. 1350089 ◽  
Author(s):  
K. L. MOHANTA ◽  
G. C. ROUT
Keyword(s):  
Specific Heat ◽  
Cuprate Superconductors ◽  
Spin Fluctuation ◽  
Mean Field ◽  
Microscopic Theory ◽  
Spin Fluctuations ◽  
Function Technique ◽  
Transverse Spin ◽  
Model Parameters ◽  
Superconducting Transition

We report here a microscopic theory of the temperature dependence of specific heat in high-Tc cuprate superconductors. The system is described by a model Hamiltonian consisting the antiferromagnetic spin fluctuations due to the impurity f-electrons as well as the conduction electrons, besides the superconducting interaction due to the itinerant electrons. The Hamiltonian is treated within a mean-field approach. The transverse spin fluctuation parameters and the superconducting gap are calculated by Zubarev's Green's function technique and solved self-consistently. The temperature dependent specific heat is calculated from the free energy in order to study the anomalies appearing at the spin fluctuation and superconducting transition temperatures. The evolutions of these anomalies are studied by varying the model parameters of the systems and results are discussed in reference to experimental observations.

ZERO—POINT SPIN FLUCTUATION EFFECTS IN ANHARMONIC WEAK ITINERANT ELECTRON MAGNETS

1993 ◽  
Vol 07 (01n03) ◽  
pp. 585-588 ◽  
Author(s):  
ALEXANDER SOLONTSOV
Keyword(s):  
Inelastic Neutron Scattering ◽  
Spin Fluctuation ◽  
Landau Theory ◽  
Zero Point ◽  
Thermal Fluctuations ◽  
Inelastic Neutron ◽  
Spin Fluctuations ◽  
Itinerant Electron ◽  
Fluctuation Effects

The spin fluctuation theory of weak itinerant magnets is critically reviewed and is shown to be well established in the weak spin anharmonicity limit. A new self—consistent approach is formulated in terms of the Landau theory of phase transitions to account for zero—point and thermal fluctuations in anharmonic itinerant magnets. The role of spin fluctuations and Fermi excitations in MnSi, Ni3Al and ZrZn2 is discussed using the inelastic neutron scattering experiments.

THE EFFECT OF PHONONS ON SPIN-FLUCTUATION SUPERCONDUCTIVITY

2007 ◽  
Vol 21 (18n19) ◽  
pp. 3075-3077 ◽  
Author(s):  
P. M. R. BRYDON
Keyword(s):  
Cuprate Superconductors ◽  
Phonon Mode ◽  
Spin Fluctuation ◽  
Spin Fluctuations ◽  
Phonon Coupling ◽  
Wave State ◽  
Static Spin ◽  
Electron Phonon Coupling ◽  
Self Consistent

We present a study of the role of phonons in the cuprate superconductors. Assuming static spin fluctuations, we find that the self-consistent d-wave state is very sensitive to both the electron-phonon coupling strength and the phonon mode considered.

scholarly journals Role of critical spin fluctuations in ultrafast demagnetization of transition-metal rare-earth alloys

2013 ◽  
Vol 87 (21) ◽  
Author(s):  
V. López-Flores ◽  
N. Bergeard ◽  
V. Halté ◽  
C. Stamm ◽  
N. Pontius ◽  
...  
Keyword(s):  
Rare Earth ◽  
Transition Metal ◽  
Spin Fluctuations ◽  
Rare Earth Alloys ◽  
Ultrafast Demagnetization

SPIN FLUCTUATION THEORY FOR TEMPERATURE-INDUCED FERROMAGNETISM IN ITINERANT ANTIFERROMAGNETS AND PARAMAGNETS

1995 ◽  
Vol 09 (10) ◽  
pp. 1171-1184 ◽  
Author(s):  
A.A. POVZNER ◽  
D.V. LIKHACHEV
Keyword(s):  
Order Parameter ◽  
Magnetic Phase ◽  
Spin Fluctuation ◽  
Density Wave ◽  
Spin Density Wave ◽  
Spin Fluctuations ◽  
Fluctuation Theory ◽  
Itinerant Electron ◽  
Electron Systems ◽  
Antiferromagnetic Transition

The possible occurrence of “temperature-induced ferromagnetism” in itinerant antiferromagnets with spin-density wave and strong paramagnets is discussed on the basis of spin fluctuation theory taking account of the effect of large ferromagnetic spin fluctuations. It is shown that the presence of a point of inflexion of the density of states near the Fermi level leads to the appearance of temperature-induced ferromagnetic order parameter in the itinerant electron systems. In addition the influence of this order parameter on the antiferromagnetic transition temperature is demonstrated and new mechanism of the magnetic phase transition is studied in relation to the magnetism of TiBe 2.

scholarly journals Modeling of the Doping Dependent Superconducting Transition Temperatures for Cuprates: Role of Antiferromagnetic Fluctuations

2008 ◽  
Vol 1 (1) ◽  
pp. 14-21
Author(s):  
Saleh Hasan Naqib
Keyword(s):  
Cuprate Superconductors ◽  
Spin Fluctuation ◽  
Spectral Weight ◽  
Spin Fluctuations ◽  
Spin Excitation ◽  
Superconducting Transition ◽  
Electronic Density ◽  
Fluctuation Frequency ◽  
Antiferromagnetic Spin

We have calculated the superconducting transition temperature, Tc, of high-Tc cuprates within the strong-coupling Bardeen-Cooper-Schrieffer (BCS) formalism. The hole pairing was attributed to the antiferromagnetic spin fluctuations. Such fluctuations are believed to exist over the whole superconducting hole concentrations, p, extending from the underdoped to the overdoped regimes. A complete consideration of the p-dependences of the antiferromagnetic spin excitation spectral weight, spin fluctuation frequency, ωsf, and the effect of the pseudogap on the electronic density of states seems to reproduce the experimental Tc(p) satisfactorily over the entire doping range. The possible implications of this finding are discussed in detail.       Keywords: Cuprate superconductors; Superconducting Tc;  Spin fluctuations; Pseudogap. © 2009 JSR Publications. ISSN: 2070-0237(Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v1i1.1181

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