Spin Waves in Exchange-Coupled Complex Magnetic Structures and Neutron Scattering

Sáenz, A. W.

doi:10.1103/physrev.125.1940

Cited by 39 publications

(18 citation statements)

References 14 publications

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“…28,29 The initial values of the magnetic coupling constants for the calculations were obtained from the DFT calculations plus a scale factor. At this stage ͑model I͒, only the dispersion curves in the ͑0 1 0͒ BZ were fitted.…”

Section: Therefore At Low Temperatures H Can Be Rewritten Asmentioning

confidence: 99%

Understanding magnetic interactions in the seriesA2FeX5⋅H2O(A=

et al. 2008

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The compounds A 2 FeX 5 ·H 2 O ͑A = alkali or NH 4 , X = Cl, Br͒ form a series of easy-axis antiferromagnets with transition temperatures in the range from 6 to 23 K, temperatures considerably higher than those of other similar hydrated salts of transition-metal ions. A study combining inelastic triple axis neutron spectroscopy ͑TAS͒ neutron scattering experiments and theoretical density functional theory ͑DFT͒ ab initio calculations of the magnetic superexchange constants has been done. A general spin-wave theory for an antiferromagnetic system with several magnetic ions in the magnetic unit cell and both uniaxial and rhombic magnetic anisotropies was employed to fit the observed magnon dispersion curves. The results obtained with the two techniques ͑TAS and DFT͒ allow us to determine with accuracy the magnetic exchange constants and therefore explain the efficiency of the superexchange pathways containing hydrogen bonds in transmitting the magnetic interactions.

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Section: Therefore At Low Temperatures H Can Be Rewritten Asmentioning

confidence: 99%

Understanding magnetic interactions in the seriesA2FeX5⋅H2O(A=

et al. 2008

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“…Conventional spin-wave theory of the Holstein-Primakoff type [17] for a 2D Heisenberg square lattice antiferromagnet with a Hamiltonian //=Z/S/S,, (1) where the sum is over nearest-neighbor spins (S = j yields a cross section (for magnon creation)…”

Section: High-energy Spin Waves In La2cu04mentioning

confidence: 99%

High-energy spin waves inLa2CuO4

et al. 1991

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Time-of-flight spectroscopy using neutrons produced by a spallation source is used to measure the one-magnon scattering throughout the Brillouin zone for La2Cu04. The zone-boundary magnons have an energy ^WZB~0.3 12 ±0.005 eV and are good eigenstates of the quantum Heisenberg Hamiltonian in that they possess lifetimes > \Q/(o. A multiplicative renormalization of the overall frequency scale of classical spin-wave theory accounts for the quantum effects in the one-magnon spectrum.PACS numbers: 75.30.Ds, 74.70.Vy, 75.10.Jm, 75.50.Ee The unusual features of Heisenberg antiferromagnets when quantum mechanics is taken into account have been investigated for much of this century. For the onedimensional case, quantum fluctuations destabilize the Neel state entirely. Even in higher dimensions, quantum fluctuations lead to significant corrections to the groundstate energy [1,2] and the spin-w^ave excitations [3] which are strongest for low spin. The discovery of hightemperature superconductivity has focused attention on La2Cu04, apparently an excellent realization of a twodimensional (2D) spin-y quantum antiferromagnet [4]. The magnetic correlations in La2Cu04 have been investigated by several microscopic techniques, most notably light scattering [5], muon spin relaxation [6][7][8], and neutron scattering [9][10][11][12][13]. Unfortunately, because of experimental limitations and restrictions in momentum and energy transfer, no technique has been able to probe the excitations over the whole Brillouin zone. We describe here a neutron-scattering investigation performed on a spallation source, in which we were able to overcome previous difficulties and observe magnetic excitations over a wide range of wave vector and energy. Well-defined zoneboundary spin waves with an energy of /ift)zB=0.312 ±0.005 eV are found. Also, the dispersion relation shows the conventional spin-wave form.Following previous practice, we use the orthorhombic nomenclature to label reciprocal space so that the basal planes are parallel to the (AO/) zone. Even though a^c, in this experiment we do not distinguish between them, for convenience, we define a* and c* to lie in the horizontal and vertical planes of the instrument, respectively. The sample was an assembly of sixteen single crystals [14] aligned such that their in-plane axes coincided to better than 1.5°. The total mass of the crystals was 0.1 kg. As described elsewhere [12], crystals were grown from CuO-rich melts contained in a large Pt crucible. The room-temperature lattice parameters were a=5.375(2) A, * = 13.156(4) A, and c=5.409(2) A. The Neel temperatures of the individual crystals ranged between 260 and 290 K.Experiments were performed on the High-Energy Transfer Spectrometer (HET) [15] at the United Kingdom spallation neutron source ISIS of the Rutherford Appleton Laboratory. HET is a "direct geometry chopper" spectrometer. High-energy (spallation) neutrons are produced when an 800-MeV pulsed proton beam with a current of 100 juA hits a uranium target. A beam of monochromatic neutrons...

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“…Single-ion anisotropy terms are extremely small in magnetite ͑with anisotropy fields of 0.1-1 T, depending on temperature͒ and are set to zero. 10,24,25 For an arbitrary number of collinear spins in the unit cell, Saenz 26 has developed a formalism to calculate the spin wave excitation energies, eigenvectors, and neutron scattering intensities. S li is the vector spin operator for the ground-state ion with spin magnitude i S i , where S i is positive and i = ± 1 with +1͑−1͒ parallel ͑antiparallel͒ to the z-quantization axis.…”

Section: Collective Spin Wave Excitationsmentioning

confidence: 99%

Investigation of the presence of charge order in magnetite by measurement of the spin wave spectrum

et al. 2006

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Inelastic neutron scattering results on magnetite ͑Fe 3 O 4 ͒ show a large splitting in the acoustic spin wave branch, producing a 7 meV gap midway to the Brillouin zone boundary at q = ͑0,0,1/2͒ and ប = 43 meV. The splitting occurs below the Verwey transition temperature, where a metal-insulator transition occurs simultaneously with a structural transformation, supposedly caused by the charge ordering on the iron sublattice. The wavevector ͑0,0,1/2͒ corresponds to the superlattice peak in the low symmetry structure. The dependence of the magnetic superexchange on changes in the crystal structure and ionic configurations that occur below the Verwey transition affect the spin wave dispersion. To better understand the origin of the observed splitting, several Heisenberg models intended to reproduce the pair-wise variation of the magnetic superexchange arising from both small crystalline distortions and charge ordering were studied. None of the models studied predicts the observed splitting, whose origin may arise from charge-density wave formation or magnetoelastic coupling.

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Spin Waves in Exchange-Coupled Complex Magnetic Structures and Neutron Scattering

Cited by 39 publications

References 14 publications

Understanding magnetic interactions in the seriesA2FeX5⋅H2O(A=

Understanding magnetic interactions in the seriesA2FeX5⋅H2O(A=

High-energy spin waves inLa2CuO4

Investigation of the presence of charge order in magnetite by measurement of the spin wave spectrum

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