Zero-point spin fluctuations and the magnetovolume effect in itinerant-electron magnetism

Solontsov, A.; Wagner, D.

doi:10.1103/physrevb.51.12410

Cited by 41 publications

(35 citation statements)

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“…This approach was shown to be valid in the opposite limit of strong SF coupling [3]. To account for spin anharmonicity beyond these limits a SM theory of SF was recently worked out basing on a variational procedure [3]. Here we use the SM tleory to analyse different regimes of the SF behaviour in itinerant electron magnets.…”

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confidence: 99%

“…Another approach is based on the constraint that the total local moment including the zeropoint and thermal SF contributions is a conserved (359) quantity (the "sum rule") [4]. This approach was shown to be valid in the opposite limit of strong SF coupling [3]. To account for spin anharmonicity beyond these limits a SM theory of SF was recently worked out basing on a variational procedure [3].…”

mentioning

confidence: 99%

“…However, a meaningful classification of SF regimes as well as an analysis of spin anharmonicity is still lacking. A conventional description of SF effects is usually based on the mode-mode coupling [1], or self-consistent renormalization (SCR) [2] theory being valid only in the limit of weak spin anharmonicity [3]. Another approach is based on the constraint that the total local moment including the zeropoint and thermal SF contributions is a conserved (359) …”

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confidence: 99%

“…To describe the mode-mode coupling of SF we use a dimensionless spin anharmonicity parameter [3] which is a measure of the stiffness of averaged squared amplitude of SF, or squared local moments, Here γ0 is the coefficient in the Μ4/4 term of the Stoner free energy as a function of the magnetic order parameter Al , ΣW = fó dω/2π, the factors N = [exp(ħω/kBT) -1] -1 and 1/2 define the thermal (M2L)T and zeropoint (Μ )Z.P. contributions to J , which also provides to distinguish the thermal g T and zero point gZ.P.…”

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confidence: 99%

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Soft-Mode vs. Localized Moments Regimes of Spin Fluctuations in Itinerant Electron Magnetism

Solontsov¹,

Lacroix

Wagner

1997

Acta Phys. Pol. A

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An analysis of different regimes of spin fluctuation behaviour in anharmonic itinerant electron magnets is presented basing on the recently worked out soft-mode theory of spin fluctuations.PALS numbers: 75.10. Lpa, 75.40.Gb, 75.50.Ee Existing experimental data in metals present direct evidence for importance of overdamped spin fluctuation (SF) with frequencies softening near some points of the Brillouin zone related to magnetic instabilities. The SF behaviour depends on the mode-mode coupling, or spin anharmonicity, and may be separated into several well-defined regimes. The Fermi liquid (FL) regime of SF arising in the low-temperature limit changes to the soft-mode (SM) one at elevated temperatures and then to the localized moments (LM) regime characterized by the Curie-Weiss susceptibility and saturated local moments. As we show here in all regimes an important role is played by quantum zeropoint SF which may give rise to strong spin anharmonicity. However, a meaningful classification of SF regimes as well as an analysis of spin anharmonicity is still lacking. A conventional description of SF effects is usually based on the mode-mode coupling [1], or self-consistent renormalization (SCR) [2] theory being valid only in the limit of weak spin anharmonicity [3]. Another approach is based on the constraint that the total local moment including the zeropoint and thermal SF contributions is a conserved (359)

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Soft-Mode vs. Localized Moments Regimes of Spin Fluctuations in Itinerant Electron Magnetism

Solontsov¹,

Lacroix

Wagner

1997

Acta Phys. Pol. A

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“…In principle, one can estimate ξ from the fluctuation-dissipation theorem, which states that (see, e.g., Refs. [24,25])…”

Section: "Beyond-lda" Critical Fluctuationsmentioning

confidence: 99%

Density Functional Calculations Near Ferromagnetic Quantum Critical Points

Mazin

Singh

Aguayo

Physics of Spin in Solids: Materials, Methods and Applications

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We discuss the application of the density functional theory in the local density approximation (LDA) near a ferromagnetic quantum critical point. The LDA fails to describe the critical fluctuations in this regime. This provides a fingerprint of a materials near ferromagnetic quantum critical points: overestimation of the tendency to magnetism in the local density approximation. This is in contrast to the typical, but not universal, tendency of the LDA to underestimate the tendency to magnetism in strongly Hubbard correlated materials. We propose a method for correcting the local density calculations by including critical spin fluctuations. This is based on (1) Landau expansion for the free energy, evaluated within the LDA, (2) lowest order expansion of the RPA susceptibility in LDA and (3) extraction of the amplitude of the relevant (critical) fluctuations by applying the fluctuation-dissipation theorem to the difference between a quantum-critical system and a reference system removed from the quantum critical point. We illustrate some of the aspects of this by the cases of Ni3Al and Ni3Ga, which are very similar metals on opposite sides of a ferromagnetic quantum critical point. LDA calculations predict that Ni3Ga is the more magnetic system, but we find that due to differences in the band structure, fluctuation effects are larger in Ni3Ga, explaining the fact that experimentally it is the less magnetic of the two materials.

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Phase Transitions and Finite Temperature Magnetism: Experiment and Analysis

Kaul

2007

Handbook of Magnetism and Advanced Magnetic Materials

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Magnetic excitations, prevailing in different temperature regimes that lie below the magnetic ordering temperature, and static critical phenomena near the thermally‐driven magnetic order–disorder phase transitions in spin systems in which the electrons responsible for magnetism are either localized or itinerant are reviewed from the experimental point of view. Besides bringing out clearly the importance of the energy and time scales governing various physical processes connected with the finite temperature magnetism and phase transitions in such systems, a brief account of the relevant theoretical background and crucial steps in the data analyses is given so as to prepare the ground for a meaningful comparison between theory and experiment. Such a comparison, in turn, is shown to provide improved understanding of the nature and origin of magnetic excitations and critical phenomena in localized‐spin and itinerant‐electron systems. In addition, this review highlights both the power as well as the limitations of the experimental techniques employed in the literature to study magnetic excitations and deals extensively with the magnon‐to‐fracton crossover in systems with localized spins and crossovers between different critical regimes in isotropic spin systems with long‐range interactions or spin systems in which long‐range interactions occur in association with magnetic anisotropy.

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Zero-point spin fluctuations and the magnetovolume effect in itinerant-electron magnetism

Cited by 41 publications

References 20 publications

Soft-Mode vs. Localized Moments Regimes of Spin Fluctuations in Itinerant Electron Magnetism

Soft-Mode vs. Localized Moments Regimes of Spin Fluctuations in Itinerant Electron Magnetism

Density Functional Calculations Near Ferromagnetic Quantum Critical Points

Phase Transitions and Finite Temperature Magnetism: Experiment and Analysis

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