Magnetic circular dichroism in 5<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi></mml:math>photoemission from Gd and Tb metal

Laan, G. van der; Arenholz, Elke; Navas, E.; Hu, Z.; Mentz, E.; Bauer, Andreas; Kaindl, G.

doi:10.1103/physrevb.56.3244

Cited by 18 publications

(11 citation statements)

References 17 publications

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“…Interestingly, the peak normalized differences (PND's) or percentage dichroisms match very well between experiment and theory. Moreover, despite using parameters derived elsewhere [22,23], a very good match is observed between the theoretical and experimental spectra and difference curves, including all of the fine structure in the 5p manifold. Over the photon energy range of 138-150 eV, other EDC pairs exhibit similar dichroic differences to that at hy 137 eV but with strong changes in the shapes of the "raw" EDC spectra and a decrease in the dichroism percentage (PND) as the photon energy moves toward the maximum of the giant resonance [26].…”

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Nature of Resonant Photoemission in Gd

Mishra¹,

Cummins

Waddill

et al. 1998

Phys. Rev. Lett.

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The phenomenon of resonant photoemission happens when, in addition to a direct photoemission channel, a second indirect channel opens up as the absorption threshold of a core level is crossed. A massive increase in emission cross section can occur, but the nature of the process remains clouded. Using novel magnetic linear dichroism in photoelectron spectroscopy experiments and theoretical calculations, we can now clearly demonstrate that temporal matching of the processes as well as energy matching is a requirement for true "resonant photoemission." [S0031-9007(98)06819-7] PACS numbers: 75.70. -i, 75.50. -y, 79.60. -i The photoemission of 4f and 5p electrons from rareearth metals and their compounds is strongly enhanced when the photon has just enough energy to excite a 4d electron to an unoccupied 4f level, leading to a process called "resonant photoemission." (See Fig. 1.) In a generic picture, the indirect channel of the resonant photoemission is interpreted as due to a process where a 4d electron in the initial state is first excited to the unoccupied 4f level, forming a tightly coupled, bound intermediate state, 4d core hole plus 4f electrons. Then a decay via autoionization occurs, producing a final state identical to that obtained by a direct photoemission process for the ejected electron [1]. The transition rate is greatly enhanced if the excited state decay is by a (super)-Coster-Kronig [(s)CK] process [2,3]. The key question is whether these processes are coherent or incoherent: Is it truly resonant photoemission or merely the incoherent addition of a second emission channel? Should the overall intensity be treated as a squaring of the sum of the amplitudes (coherent) or summing of the squares of the amplitudes (incoherent)? A true resonant photoemission process should be coherent, involving interference terms between the direct photoemission and indirect photoemission channels. Possibly, incoherence would give rise to the loss of photoemission characteristics in the process, with a domination of Auger-like properties.To this problem we have applied the new photoelectron spectroscopy technique of magnetic linear dichroism in angular distributions (MLDAD) [4][5][6][7]. This technique is related to but distinct from the techniques of magnetic x ray circular dichroism (MXCD) in photoelectron spectroscopy and x ray absorption [8][9][10][11][12][13]. The key is that while strong MXCD effects in ferromagnets can be observed with photoemission and absorption, the large MLDAD effect in ferromagnets is solely a photoemission, not an absorption-driven, process. This is because the chirality which gives rise to magnetic sensitivity is due to the vectorial configuration in MLDAD as opposed to the FIG. 1. (a) Schematic diagram of the direct and indirect channels in Gd 4f resonant photoemission. Time estimates are based on Refs. [2,3]. (b) Same for Gd 5p emission. (c) Comparison of coherent and incoherent additions of channel contributions. A0 (AI) is the direct (indirect) amplitude. (d) The photoabsorption of Gd͞...

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“…All parameters were taken the same as in Refs. [13,23] and not adapted to suit the current measurements. Interference terms between the photoemission final state continua with orbital quantum numbers 1 2 1 and 1 1 1 were fully taken into account as needed for MLDAD [21].…”

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confidence: 99%

Nature of Resonant Photoemission in Gd

Mishra¹,

Cummins

Waddill

et al. 1998

Phys. Rev. Lett.

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“…[60][61][62] In the 3d transition-metal series, metallic nickel is a typical example of a correlated electron system, where the PE spectrum shows distinct satellite structure, which means that several 3d n configurations are involved. 59 Other 3d metals, such as cobalt, have satellites that are substantially weaker, 63 which indicates that the satellite structure depends on the mixing of a large number of 3d n configurations.…”

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confidence: 99%

Valence fluctuations in thin films and theαandδphases of Pu metal determined by4fcore-level photoemission calculations

Laan

Taguchi

2010

Phys. Rev. B

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The average number of 5f electrons making up the valence state in plutonium metal together with the electronic fluctuations on each metal site has been a recent subject of debate. For the ␦ phase of Pu, where compared to the ␣ phase increased localization ͑more atomiclike character͒ leads to decreased overlap and volume increase, an f count close to either 5 or 6 has been proposed depending on the type of electronic structure calculation. In order to resolve the controversy, we analyze the Pu 4f photoemission spectrum, which displays well screened and poorly screened peaks that can be used as a measure for the degree of localization. A simple analytical two-level model already shows on general grounds that the f count for Pu must be between 5 and 5.5. Furthermore, we present detailed Anderson impurity model calculations including the full multiplet structure for Pu 4f photoemission, which are compared to previous experimental results obtained from 1 to 9 monolayers thin films of Pu on Mg and from Pu metal in the ␣ and ␦ phases. The trend in the satellite to main peak intensity ratio as a function of the Pu layer thickness gives a clear indication that Pu metal has an 5f 5 like ground state. For the Pu allotropes and thicker films an f count of 5.22 is obtained with a Coulomb interaction U = 4 eV. The 5f fluctuations in Pu metal are very prominent and strongly material dependent. The calculations give a ground state with 9.6% f 4 , 58.8% f 5 , and 31.6% f 6 for the ␣ phase and 5.7% f 4 , 66.4% f 5 , and 27.8% f 6 for the ␦ phase while for the thin films the amount of f 5 and the localization strongly increase with reduced thickness. The obtained findings are in agreement with recent electronic structure calculations for ␦ Pu using local-density approximation with dynamical mean-field theory and with the branching-ratio analysis of the Pu N 4,5 edge in electron-energy-loss spectroscopy.

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“…17 This has been confirmed for localized systems, such as the rare-earth metals, where the PE displays detailed multiplet structure due to Coulomb and exchange interactions. [18][19][20] It is therefore timely to study also materials at the borderline of itinerant and localized behavior. Nickel metal is an obvious choice, despite the fact that its MCD signal is much weaker than in Fe and Co metal due to the large amount of d 10 character in the final state.…”

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confidence: 99%

On-site Coulomb interaction and exchange splitting in Ni2pphotoemission of ferromagnetic nickel

2000

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The 2p photoemission of Ni metal displays a weak magnetic circular dichroism ͑MCD͒ with a complex structure over an energy range of more than 35 eV. Since a one-particle model clearly fails to explain this experimental result, we propose a final-state impurity model which assumes that the core-ionized atom can be described as an impurity state in a many-body approach. From this model we obtain the value of the on-site Coulomb interaction U without having to rely on assumptions concerning the nature of the ground state, which might be either localized or itinerant. The pd 8 satellite, which is much more pronounced in the MCD than in the isotropic spectrum, can be used to fix the value of U to ϳ5.15 eV. We demonstrate that an Anderson impurity model would require different values of U and transfer integral, T, in initial and final state. We further present the calculated spin-polarized Ni 2p photoemission. Its 2p 1/2 structure shows distinct differences with the MCD, which means that the 2p3d Coulomb interaction cannot be neglected with respect to the 2p spin-orbit interaction.

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Magnetic circular dichroism in 5pphotoemission from Gd and Tb metal

Cited by 18 publications

References 17 publications

Nature of Resonant Photoemission in Gd

Nature of Resonant Photoemission in Gd

Valence fluctuations in thin films and theαandδphases of Pu metal determined by4fcore-level photoemission calculations

On-site Coulomb interaction and exchange splitting in Ni2pphotoemission of ferromagnetic nickel

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