Magnon spectrum and related finite-temperature magnetic properties: A first-principle approach

Halilov, S. V.; Perlov, A. Ya.; Oppeneer, Peter M.; Eschrig, H.

doi:10.1209/epl/i1997-00319-x

Cited by 87 publications

(64 citation statements)

References 27 publications

(35 reference statements)

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“…It has been argued 84 that such a "rigid" band structure cannot be used to describe demagnetization due to spin excitations. It may be noted that it has been shown 85,86 previously that such zero-temperature band structure can very well be employed to accurately compute the transversal spin-excitation energy spectra of Fe, Co, and Ni, as well as their temperature-dependent magnetization M(T ). However, as prior to our calculations, no ab initio calculations of the longitudinal Elliott-Yafet electron-phonon spin-flip spectrum existed (to the best of our knowledge), we can presently not state how accurate such calculations are, but we may note (1) that our calculation for Al is in good agreement with an earlier work 56 and (2) the recently published independent computational investigation 47 obtained very similar demagnetization fractions in the thermalized regime.…”

Section: Discussionmentioning

confidence: 99%

Ab initiotheory of electron-phonon mediated ultrafast spin relaxation of laser-excited hot electrons in transition-metal ferromagnets

et al. 2013

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We report a computational theoretical investigation of electron spin-flip scattering induced by the electronphonon interaction in the transition-metal ferromagnets bcc Fe, fcc Co, and fcc Ni. The Elliott-Yafet electronphonon spin-flip scattering is computed from first principles, employing a generalized spin-flip Eliashberg function as well as ab initio computed phonon dispersions. Aiming at investigating the amount of electronphonon mediated demagnetization in femtosecond laser-excited ferromagnets, the formalism is extended to treat laser-created thermalized as well as nonequilibrium, nonthermal hot electron distributions. Using the developed formalism we compute the phonon-induced spin lifetimes of hot electrons in Fe, Co, and Ni. The electron-phonon mediated demagnetization rate is evaluated for laser-created thermalized and nonequilibrium electron distributions. Nonthermal distributions are found to lead to a stronger demagnetization rate than hot, thermalized distributions, yet their demagnetizing effect is not enough to explain the experimentally observed demagnetization occurring in the subpicosecond regime.

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Section: Discussionmentioning

confidence: 99%

Ab initiotheory of electron-phonon mediated ultrafast spin relaxation of laser-excited hot electrons in transition-metal ferromagnets

et al. 2013

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“…3 The spatial resolution of such techniques is chosen in view of the problem at hand and numerical considerations, but the equation of motion is always the same. At the most finely resolved and microscopic end of the modeling spectrum there are atomistic spin models, 4 which have been proved to be a powerful tool for approaching the extreme phenomenology of the ultrafast magnetization dynamics. 5,6 In these one associates individual classical spin vectors S i to all magnetic atoms, which are then coupled through a time-independent Heisenberg Hamiltonian,…”

Section: Introductionmentioning

confidence: 99%

Dynamical exchange interaction from time-dependent spin density functional theory

Stamenova

Sanvito

2013

Phys. Rev. B

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We report on ab initio time-dependent spin-dynamics simulations for a two-center magnetic molecular complex within the framework of the time-dependent noncollinear spin-density functional theory. In particular, we discuss how the dynamical behavior of the ab initio spin-density in the time domain can be mapped onto a model Hamiltonian based on the classical Heisenberg spin-spin interaction J S 1 · S 2 . By analyzing individual localizedspin trajectories, extracted from the spin-density evolution, we demonstrate a practical method for evaluating the effective Heisenberg exchange coupling constant J from first-principles simulations. We find that J , extracted in such a dynamical way, agrees quantitatively with that calculated by the standard density functional theory broken-symmetry scheme.

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“…From this information we then obtain related modifications of J i j , and predictions of the meanfield theory and random-phase approximation for the pressure dependence of T c . For the determination of the spin-wave spectra we use the method of Grotheer et al, 10 which is an alternative to the so-called frozen-magnon method introduced by Halilov et al 11 Thereby, a spiral external field is applied, which for a monatomic unit cell has the formwhere q is the wave vector of the spiral and T denotes the translation vectors of the atomic lattice. The field is constant within each atomic sphere.…”

mentioning

confidence: 99%

Ab initioelectron theory for magnetism in Fe: Pressure dependence of spin-wave energies, exchange parameters, and Curie temperature

2003

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The spin-wave spectra for bcc Fe at various lattice constants are calculated by the ab initio density functional electron theory for various lattice constants, and the exchange parameters of a Heisenberg model are determined from the data. The spin-wave energies increase with decreasing lattice constant, and the behavior of the exchange parameters can by no means be described by the Bethe-Slater curve for an effective nearest-neighbor Heisenberg model. From the spin-wave frequencies the pressure dependence of the Curie temperature is derived in mean-field and random-phase approximation, yielding ‫ץ‬T c MF /‫ץ‬pϷ1.6 K/kbar and ‫ץ‬T c RPA /‫ץ‬p Ϸ1.8 K/kbar, in contrast to the experimental result ‫ץ‬T c /‫ץ‬pϷ0. Possible reasons for this discrepancy are discussed. The exchange interactions in 3d transition metals and their compounds are often discussed within the framework of an effective nearest-neighbor Heisenberg model and the Bethe-Slater curve ͑see, e.g., Ref. 1͒ which represents a conjecture on the variation of the nearest-neighbor exchange parameter J(R) with the interatomic spacing R. According to this curve, J(R) increases with decreasing R for Co and Ni, whereas it decreases for Fe and changes sign from positive to negative for small R. As an example for the application of the Bethe-Slater curve, the temperature dependence of the magnetization of an amorphous ferromagnet was explained 2 by a mean-field approach with spatial fluctuations of J estimated by use of this curve. If this simple nearest-neighbor Bethe-Slater model was correct, then the critical temperature T c of body-centered-cubic Fe as calculated in mean-field theory would be expected to decrease strongly when pressure is exerted on the sample. Experimentally, however, nearly no change of T c was found 3 at pressures up to the structural transition from body-centered to face-centered.Indeed, calculations based on the ab initio densityfunctional electron theory have revealed ͑Table I͒ that the simple nearest-neighbor Heisenberg model fails badly for Fe. Instead, an effective Heisenberg model with long-range pair interaction parameters J i j is proposed,where e i and e j are the unit vectors pointing in directions of the local magnetic moments at sites (i, j), respectively. The exchange parameters remain non-negligible over a very long range, and they oscillate in sign ͑Table I͒. It is the objective of this paper to calculate, by ab initio density-functional theory, the change of the spin-wave spectrum with decreasing lattice constant. From this information we then obtain related modifications of J i j , and predictions of the meanfield theory and random-phase approximation for the pressure dependence of T c . For the determination of the spin-wave spectra we use the method of Grotheer et al., 10 which is an alternative to the so-called frozen-magnon method introduced by Halilov et al. 11 Thereby, a spiral external field is applied, which for a monatomic unit cell has the formwhere q is the wave vector of the spiral and T denotes the translation...

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Magnon spectrum and related finite-temperature magnetic properties: A first-principle approach

Cited by 87 publications

References 27 publications

Ab initiotheory of electron-phonon mediated ultrafast spin relaxation of laser-excited hot electrons in transition-metal ferromagnets

Ab initiotheory of electron-phonon mediated ultrafast spin relaxation of laser-excited hot electrons in transition-metal ferromagnets

Dynamical exchange interaction from time-dependent spin density functional theory

Ab initioelectron theory for magnetism in Fe: Pressure dependence of spin-wave energies, exchange parameters, and Curie temperature

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