Suppression of Standing Spin Waves in Low-Dimensional Ferromagnets

Taroni, A.; Bergman, Anders; Bergqvist, Lars; Hellsvik, Johan; Eriksson, Olle

doi:10.1103/physrevlett.107.037202

Cited by 25 publications

(21 citation statements)

References 28 publications

(63 reference statements)

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“…12 is at variance with a recent theoretical study attempting to explain the absence of standing spin waves in previous experiments. 23 The clear sign of a second mode for wave vectors q = 0.174 and 0.261Å −1 in Fig. 12, as well as its absence in the spectral densities for q 0.348 A −1 , is in agreement with the experimental results in Fig.…”

Section: Theorysupporting

confidence: 86%

“…14,15,21,22 On the other hand, a recent dynamical analysis of the Heisenberg model showed a complete suppression of standing modes at low wave vectors and at room temperature. 23 Because of these open questions and contradictions we decided to revisit the issue of surface spin waves in fcc cobalt films deposited on Cu(100). We focus on the eight-monolayer (ML) cobalt film, first, because most of the previous data concern that system; secondly, because the experimental data of Etzkorn et al 7 show that the surface spin wave is practically independent of the number of layers beyond five monolayers.…”

Section: Introductionmentioning

confidence: 99%

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Surface spin waves of fcc cobalt films on Cu(100): High-resolution spectra and comparison to theory

et al. 2012

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With the help of a recently developed electron energy-loss spectrometer we have studied the surface spin waves on an eight-monolayer cobalt film deposited on Cu(100) surfaces with unprecedented energy resolution. Standing waves of the bulk of the film are discovered in the region of small wave vectors q < 0.35Å −1 . The dispersion of surface spin waves is isotropic even for large q . Because of the high-energy resolution and the complete characterization of the electron optical properties of the spectrometer reliable data for the linewidth of the surface spin waves are obtained. As a byproduct the dispersion of the Rayleigh surface phonon was measured. Data are compared to theoretical spin wave spectra extracted from calculations of the transverse spin susceptibility based on an ab initio electronic structure that incorporates both the metallic substrate and the magnetic film. The calculation takes fully into account the itinerant nature of the electrons responsible for the magnetic moments. The agreement between theoretical and experimental spin wave energies and linewidths is remarkably good.

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Section: Theorysupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Surface spin waves of fcc cobalt films on Cu(100): High-resolution spectra and comparison to theory

et al. 2012

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“…We note in passing that the strong signature of the standing modes in the spectra is at variance with the conclusions of Taroni et al [33]. The reason for the discrepancy is that Taroni et al erroneously assumed that all layers inside the film contribute to the scattering amplitude with the same weight, as would be the case in inelastic neutron scattering.…”

contrasting

confidence: 57%

Standing Spin Waves in Ultrathin Magnetic Films: A Method to Test for Layer-Dependent Exchange Coupling

2014

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We introduce a method to test theoretical models for the layer dependence of exchange coupling constants in ultrathin magnetic films. The method is based on the observation of high-energy and highmomentum standing spin wave modes using high-resolution electron energy loss spectroscopy. Experimental data are presented for 5-8 layers of fcc cobalt deposited on Cu(100). The power of the method is illustrated by comparison to two theoretical studies predicting rather different results concerning the ratio of the interlayer and intralayer exchange coupling constants near the surface. Only the theory with a large interlayer coupling shows sufficient energy spreading in the layer dependence of the dispersion curves to match the experimental data. We furthermore discuss the reason for the surprising success of the simple nearest-neighbor Heisenberg model with a single exchange constant matched to experiment. DOI: 10.1103/PhysRevLett.112.127202 PACS numbers: 75.30.Ds The magnetic properties of thin films present an active field in contemporary research, partly because of the importance of magnetic films in information technology, partly because of the scientific challenges involved in our fundamental understanding of magnetism. For several decades, the interplay between finite dimensions, lowered symmetry and the crystallography of thin epitaxial films and the magnetic properties such as the orientation of the easy axis, the magnetization hysteresis, and the nature of domain walls have been studied [1][2][3][4][5]. Motivated by the emergence of atomic scale probes, the focus has lately shifted to the magnetic properties of individual atoms located at the surface or at the interface and specific magnetic ordering phenomena that appear there [6][7][8][9][10][11]. The two most fundamental properties of atoms determining the magnetic order are the magnetic moments of atoms and the exchange coupling between them.Concerning the magnetic moments of atoms in ferromagnetic films, theory and experiment have painted a clear picture. Theoretical studies predict an enhancement of the magnetic moments at surfaces and a reduction in the layer adjacent to nonferromagnetic substrates [12][13][14][15]. Moments inside an adjacent nonferromagnetic substrate may be enlarged [16]. Experimental studies on magnetic moments of atoms using x-ray magnetic circular dichroism [17][18][19] confirm these conclusions.With regard to layer dependence of exchange coupling constants between atoms, the situation is less clear. Theoretical papers have come to contradictory conclusions. Experimental methods to probe for the layer specificity of the exchange coupling are hitherto unknown. For the specific case of fcc cobalt films deposited on Cu(100), e.g., Costa et al. found an enhancement of the surface intralayer exchange coupling by 90% and by 40% in the layer next to the substrate interface [20]. The interlayer exchange coupling between the surface layer and the next layer underneath was also found to be enhanced, but much less so. Layers second to th...

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“…The factor A l l describes how the experimental probes (electrons, for instance) couple to the intrinsic spin-wave excitations, and has assumed many forms in the literature. Taroni et al 27 consider A l l = e iq·R l l , with R l l = R l − R l , and they show that this choice leads to the suppression of the optical spin-wave modes in S(q, ω). With this particular choice, the probed system is excited uniformly which leads to the acoustic mode only.…”

Section: B Link To Inelastic Scattering Experimentsmentioning

confidence: 99%

First-principles investigation of spin-wave dispersions in surface-reconstructed Co thin films on W(110)

2017

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We computed spin-wave dispersions of surface-reconstructed Co films on the W(110) surface in the adiabatic approximation. The magnetic exchange interactions are obtained via first-principles electronic-structure calculations using the Korringa-Kohn-Rostoker Green-function method. We analyze the strength and oscillatory behavior of the intralayer and interlayer magnetic interactions and investigate the resulting spin-wave dispersions as a function of the thickness of Co films. In particular, we highlight and explain the strong impact of hybridization of the electronic states at the Co-W interface on the magnetic exchange interactions and on the spin-wave dispersions. We compare our results to recent measurements based on electron-energy-loss spectroscopy [E. Michel, H. Ibach, and C.M. Schneider, Phys. Rev. B 92, 024407 (2015)]. Good overall agreement with experimental findings can be obtained by considering the possible overestimation of the spin splitting, stemming from the local-spin-density approximation, and adopting an appropriate correction.

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Suppression of Standing Spin Waves in Low-Dimensional Ferromagnets

Cited by 25 publications

References 28 publications

Surface spin waves of fcc cobalt films on Cu(100): High-resolution spectra and comparison to theory

Surface spin waves of fcc cobalt films on Cu(100): High-resolution spectra and comparison to theory

Standing Spin Waves in Ultrathin Magnetic Films: A Method to Test for Layer-Dependent Exchange Coupling

First-principles investigation of spin-wave dispersions in surface-reconstructed Co thin films on W(110)

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