Positive spin polarization of the photoelectrons emitted near photothreshold from cesiated Co (0001)

Gröbli, J. C.; Kündig, A.A.; Meier, F.; Siegmann, H. C.

doi:10.1016/0921-4526(94)00287-6

Cited by 11 publications

(6 citation statements)

References 16 publications

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“…However, the large spin polarization of the 2PPE yield is not a conclusive proof of the spin filter effect, since different excitation processes and, hence, transition matrix elements have to be considered in 2PPE compared to regular photoemission induced by absorption of a single photon. The marked drop in P at the highest kinetic energies (corresponding to initial state energies around E F ) is consistent with single photon threshold photoemission experiments on thick Co(001) films, where P decreases from 40% to 20% on approaching the photothreshold [23]. This decrease in P has been attributed to the fact that Co is a strong ferromagnet and, hence, has no majority-spin d density of states at E F .…”

supporting

confidence: 80%

“…3), the spin polarization does not show very much structure. Even more remarkable, the maximum spin polarization value is about 65%, which is 1.5 times higher than values obtained in single photon threshold photoemission experiments [23]. The occurrence of this enhanced spin polarization is consistent with the existence of a spin filter effect in Co, as it preferentially depletes the population of the excited minority-spin electrons during the first and the second excitation process.…”

supporting

confidence: 62%

“…This decrease in P has been attributed to the fact that Co is a strong ferromagnet and, hence, has no majority-spin d density of states at E F . That P is positive even at the photothreshold has been one of the main arguments for the spin filter process [23]. At the lowest kinetic energies in the 2PPE spectrum, however, the drop in P might be generated by the growing importance of secondary electrons.…”

mentioning

confidence: 99%

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Ultrafast Spin-Dependent Electron Dynamics in fcc Co

et al. 1997

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The spin dependence of the lifetime of electrons excited in ferromagnetic cobalt is measured directly in a femtosecond real-time experiment. Using time-and spin-resolved two photon photoemission, we show that the lifetime of majority-spin electrons at 1 eV above the Fermi energy is twice as long as that of minority-spin electrons. The results demonstrate the feasibility of studying spin-dependent electron relaxation in ferromagnetic solids directly in the time domain and provide a basis for understanding the dynamics of electron transport in ferromagnetic solids and thin films. [S0031-9007(97)04853-9]

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confidence: 80%

supporting

confidence: 62%

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confidence: 99%

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Ultrafast Spin-Dependent Electron Dynamics in fcc Co

et al. 1997

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“…This theory of renormalized one-electron states has been discussed in the present context by Anderson [2], Doniach [3], Gutzwiler [4], and many others [5]. However, it could never explain the fact that no negative spin polarization is detected in photoemission from states near the Fermi energy E F in Co [6,7]. This and many other features observed in emission of low energy electrons from transition metals are now understood by considering the scattering of the excited electron on the partially filled d states of all of the atoms encountered in transport through the transition metal [8].…”

Section: Total Scattering Cross Section and Spin Motion Of Low Energymentioning

confidence: 86%

Total Scattering Cross Section and Spin Motion of Low Energy Electrons Passing through a Ferromagnet

et al. 1998

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It is shown that the spin asymmetry of the elastic transmission of electrons through ferromagnetic films can approach unity. The polycrystalline Co films are a few nanometers thick and saturated with the magnetization M in the plane. The contribution of spin-productive scattering events is below 5%. If the electron spin at incidence is chosen to be perpendicular to M, it rotates into the direction of M and also precesses around it. [S0031-9007(98)07521-8] PACS numbers: 73.50.Yg, 79.20.Kz The application of polarized electron beams to the study of magnetism took its beginning when the first spinpolarized electrons were obtained by photoemission from magnetic materials [1]. The most obvious way of looking at photoemission of electrons theoretically is to assume that the fast photoelectron does not interact appreciably with the other electrons in the metal so that the photoemission experiment often is thought of as measuring the energy spectrum of its own hole state left behind. This theory of renormalized one-electron states has been discussed in the present context by Anderson [2], Doniach [3], Gutzwiler [4], and many others [5]. However, it could never explain the fact that no negative spin polarization is detected in photoemission from states near the Fermi energy E F in Co [6,7]. This and many other features observed in emission of low energy electrons from transition metals are now understood by considering the scattering of the excited electron on the partially filled d states of all of the atoms encountered in transport through the transition metal [8]. To study this important phenomenon more thoroughly, we have measured the total scattering cross section as a function of electron energy. In contrast to numerous earlier investigations [9], we have observed very large transmission asymmetries A of up to 80% with an electron beam passing through a thin ferromagnet depending on whether its spin is parallel or antiparallel to the magnetization M. Furthermore, when the spin polarization vector P 0 of the incident electron beam is chosen to be perpendicular to M, then it rotates into the direction of M and simultaneously also precesses around M. There is a complete analogy to the magneto-optic phenomena observed when a light beam passes through ferromagnetic material. But, even when measured on the length scale of the penetration depth, the magneto-"optic" effects observed with electron beams are at least 1 order of magnitude larger as compared to those observed with light beams. This arises because the electron beam couples directly to the magnetization, while the coupling of the light beam must be mediated by the spin-orbit interaction. The observations presented here have a number of immediate important implications. For instance, the scattering cross section governs the nonequilibrium magnetization dynamics which is presently at the forefront of fundamental research in magnetism [10][11][12][13]. Furthermore, experiments of the type described here might help to improve the performance of spin filters, spin ...

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“…For the purely ballistic transport (a/l ↑ → 0, where l ↑ (l ↓ ) is the majority (minority) electrons mean free path) all integrals in Eqs. (18), (19) are evaluated analytically, and magnetoresistance reads…”

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confidence: 99%

Ballistic versus diffusive magnetoresistance of a magnetic point contact

2001

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The quasiclassical theory of a nanosize point contacts (PC) between two ferromagnets is developed. The maximum available magnetoresistance values in PC are calculated for ballistic versus diffusive transport through the area of a contact. In the ballistic regime the magnetoresistance in excess of few hundreds percents is obtained for the iron-group ferromagnets. The necessary conditions for realization of so large magnetoresistance in PC, and the experimental results by García et al are discussed.PACS numbers: 74.80. Dm, 74.50.+r, In recent experiments on study of Ni-Ni and Co-Co point contacts (PC), a surprisingly high negative magnetoresistance exceeding 200% has been discovered. 1,2 The set up of the experiment was typical for observation of giant magnetoresistance (GMR), the effect observed earlier in hybrid systems involving ferromagnetic and normal multilayer metals. 3,4 However, for the multilayer structures the typical change of the resistance reached 10% − 30%, which is considerably lower than the corresponding values of Refs. 1,2. So, one can come easily to the conclusion that the main contribution to the MR comes from the region of the PC.A negative magnetoresistance can be due to scattering on domain walls (DW) and this effect has been considered in a number of works 5-8 giving typical values of MR in a range of few percents. Such considerably low values of the MR were obtained assuming that realistic widths of the DW were large, which resulted in a low scattering amplitudes. Considering sharp DW in the ballistic regime one comes to values ∼ 70%. 8 The fact that a sharp DW may give large MR was used in Ref. 2 to explain the anomalously large values of MR in the experiments on the point contacts. 1,2 However, the theory in Ref. 2 is the perturbation theory, it can not be applied to the explanation of 300% effect. The diminishing of the width of DW, when decreasing the size of the constriction was demonstrated by Bruno. 9 The DW width becomes comparable with PC length, and magnetization rotates almost abruptly inside the constriction. This conclusion holds until the diameter of PC is smaller than its actual length. With further increase of constriction size (diameter) the wall will bend outside of PC, and simple energy considerations show that the DW width will be of the order of PC size. 10

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Positive spin polarization of the photoelectrons emitted near photothreshold from cesiated Co (0001)

Cited by 11 publications

References 16 publications

Ultrafast Spin-Dependent Electron Dynamics in fcc Co

Ultrafast Spin-Dependent Electron Dynamics in fcc Co

Total Scattering Cross Section and Spin Motion of Low Energy Electrons Passing through a Ferromagnet

Ballistic versus diffusive magnetoresistance of a magnetic point contact

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