The temperature dependence of the spin polarization of field emitted electrons from a W-EuS-vacuum junction

Baum G, Kisker E, Mahan AH, Schröder K. The temperature dependence of the spin polarization of field emitted electrons from a W-EuS-vacuum junction. Journal of Magnetism and Magnetic Materials. 1976;3(1-2):4-6.We have measured the temperature dependence P(T) of the electron spin polarization of field emitted electrons from a W-EuS-vacuum junction. The shapes of the P(T) curves depend strongly on the annealing temperature of the EuS layer. Annealed at some temperature between 300°C and 600°C the polarization drops to zero at about 16 ± 2 K

Correlation Functions and Spin

The k-electron correlation function of a free chaotic electron beam is derived with the spin degree of freedom taken into account. It is shown that it can be expressed with the help of correlation functions for a polarized electron beam of all orders up to k and the degree of spin polarization. The form of the correlation function suggests that if the electron beam is not highly polarized, observing multi-particle correlations should be difficult. The result can be applied also to chaotic photon beams, the degree of spin polarization being replaced by the degree of polarization.Comment: 6 pages, 1 eps figure, accepted to Phys. Rev.

Spin-filter effect of the europium chalcogenides: An exactly solved many-body model

A model Hamiltonian is introduced which considers the main features of the experimental spin filter situation as s-f interaction, planar geometry and the strong external electric field. The proposed many-body model can be solved analytically and exactly using Green functions. The spin polarization of the field-emitted electrons is expressed in terms of spin-flip probabilities, which on their part are put down to the exactly known dynamic quantities of the system. The calculated electron spin polarization shows remarkable dependencies on the electron velocity perpendicular to the emitting plane and the strength of s-f coupling. Experimentally observed polarization values of about 90% are well understood within the framework of the proposed model.Comment: accepted (Physical Review B); 10 pages, 11 figures; http://orion.physik.hu-berlin.de

A Left-handed β Helix Revealed by the Crystal Structure of a Carbonic Anhydrase from the Archaeon Methanosarcina thermophila

A carbonic anhydrase from the thermophilic archaeon Methanosarcina thermophila that exhibits no significant sequence similarity to known carbonic anhydrases has recently been characterized. Here we present the structure of this enzyme, which adopts a left-handed parallel β-helix fold. This fold is of particular interest since it contains only left-handed crossover connections between the parallel β-strands, which so far have been observed very infrequently. The active form of the enzyme is a trimer with three zinc-containing active sites, each located at the interface between two monomers. While the arrangement of active site groups differs between this enzyme and the carbonic anhydrases from higher vertebrates, there are structural similarities in the zinc coordination environment, suggestive of convergent evolution dictated by the chemical requirements for catalysis of the same reaction. Based on sequence similarities, the structure of this enzyme is the prototype of a new class of carbonic anhydrases with representatives in all three phylogenetic domains of life

Dynamical coherent-potential approximation approach to excitation spectra in 3d transition metals

First-principles dynamical CPA (Coherent-Potential Approximation) for electron correlations has been developed further by taking into account higher-order dynamical corrections with use of the asymptotic approximation. The theory is applied to the investigations of a systematic change of excitation spectra in $3d$ transition metals from Sc to Cu at finite temperatures. It is shown that the dynamical effects damp main peaks in the densities of states (DOS) obtained by the local density approximation to the density functional theory, reduce the band broadening due to thermal spin fluctuations, create the Mott-Hubbard type bands in the case of fcc Mn and fcc Fe, and create a small hump corresponding to the `6 eV' satellite in the case of Co, Ni, and Cu. Calculated DOS explain the X-ray photoelectron spectroscopy data as well as the bremsstrahlung isochromat spectroscopy data. Moreover, it is found that screening effects on the exchange energy parameters are significant for understanding the spectra in magnetic transition metals.Comment: To be published in Phys. Rev.

Very large magnetoimpedance effect in FeCoNi ferromagnetic tubes with high order magnetic anisotropy

[EN] The extraordinarily high (up to 800% magnetoimpedance ratio) and sensitive magnetoimpedance effect has been found and studied in FeCoNi magnetic tubes electroplated onto CuBe nonmagnetic wire at frequency of about 1 MHz order. Special annealing was done in order to induce magnetic anisotropy. The high harmonic response has been studied, and the harmonics show larger variations with the external magnetic field than the fundamental. This huge sensitivity of the harmonics (up to an order of the tens of thousands %/Oe) is promising in regard to the increase of the sensitivity of giant magnetoimpedance sensors. To explain the experiment results, we calculated the high frequency transverse susceptibility taking into account the magnetic anisotropy of first and second orders. The susceptibility is extremely high at the points of orientational phase transitions in the magnetic layer which gives rise to strong nonlinear effects. (C) 2001 American Institute of Physics.S62806286901

Nonlinear magnetoimpedance effect in FeCoNi ferromagnetic tubes

[EN] The very high (up to 820% of the magnetoimpedance ratio) and sensitive nonlinear giant magnetoimpedance effect has been studied in the FeCoNi magnetic tubes electroplated onto Cu(3%)Be nonmagnetic wire for frequencies from 1-10 MHz. Special annealing was carried out in order to induce the magnetic anisotropy. The high harmonic generation was observed and the harmonics show larger variations with the external magnetic field than the fundamental frequency. The super high sensitivity of the harmonics is promising as regards the increase of the sensitivity of magnetoimpedance sensors.Kurlyandskaya, G.; Yakabchuk, H.; Kisker, E.; Bebenin, N.; García Miquel, ÁH.; Vazquez, M.; Vas'kovskiy, V. (2001). Nonlinear magnetoimpedance effect in FeCoNi ferromagnetic tubes. Chinese Physics Letters. 18(9):1268-1270. doi:10.1088/0256-307X/18/9/337S12681270189Beach, R. S., & Berkowitz, A. E. (1994). Giant magnetic field dependent impedance of amorphous FeCoSiB wire. Applied Physics Letters, 64(26), 3652-3654. doi:10.1063/1.111170Panina, L. V., & Mohri, K. (1994). Magneto‐impedance effect in amorphous wires. Applied Physics Letters, 65(9), 1189-1191. doi:10.1063/1.112104Sommer, R. L., & Chien, C. L. (1996). Giant magneto-impedance effects in Metglas 2705M. Journal of Applied Physics, 79(8), 5139. doi:10.1063/1.361533Kurlyandskaya, G. V., Garcı́a-Beneytez, J. M., Vázquez, M., Sinnecker, J. P., Lukshina, V. A., & Potapov, A. P. (1998). The influence of field- and stress-induced magnetic anisotropy on the magnetoimpedance in nanocrystalline FeCuNbSiB alloys. Journal of Applied Physics, 83(11), 6581-6583. doi:10.1063/1.367925Kurlyandskaya, G. V., Vázquez, M., Muñoz, J. L., García, D., & McCord, J. (1999). Effect of induced magnetic anisotropy and domain structure features on magnetoimpedance in stress annealed Co-rich amorphous ribbons. Journal of Magnetism and Magnetic Materials, 196-197, 259-261. doi:10.1016/s0304-8853(98)00805-1You-Yong, D., Shu-Qin, X., Yi-Hua, L., Lin, Z., Hou-Zheng, W., & Yan-Zhong, Z. (2001). Frequency and Field Dependences of Giant Magneto-Impedance Effect in Sandwiched FeCuCrVSiB Films. Chinese Physics Letters, 18(2), 272-274. doi:10.1088/0256-307x/18/2/340Chen, D.-X., Muñoz, J. L., Hernando, A., & Vázquez, M. (1998). Magnetoimpedance of metallic ferromagnetic wires. Physical Review B, 57(17), 10699-10704. doi:10.1103/physrevb.57.10699Usov, N. A., Antonov, A. S., & Lagar’kov, A. N. (1998). Theory of giant magneto-impedance effect in amorphous wires with different types of magnetic anisotropy. Journal of Magnetism and Magnetic Materials, 185(2), 159-173. doi:10.1016/s0304-8853(97)01148-7Panina, L. ., & Mohri, K. (2000). Magneto-impedance in multilayer films. Sensors and Actuators A: Physical, 81(1-3), 71-77. doi:10.1016/s0924-4247(99)00089-8Gromov, A., & Korenivski, V. (2000). Electromagnetic analysis of layered magnetic/conductor structures. Journal of Physics D: Applied Physics, 33(7), 773-779. doi:10.1088/0022-3727/33/7/304Beach, R. S., Smith, N., Platt, C. L., Jeffers, F., & Berkowitz, A. E. (1996). Magneto‐impedance effect in NiFe plated wire. Applied Physics Letters, 68(19), 2753-2755. doi:10.1063/1.115587Kurlyandskaya, G. V., Barandiarán, J. M., Muñoz, J. L., Gutiérrez, J., Vázquez, M., Garcia, D., & Vas’kovskiy, V. O. (2000). Frequency dependence of giant magnetoimpedance effect in CuBe/CoFeNi plated wire with different types of magnetic anisotropy. Journal of Applied Physics, 87(9), 4822-4824. doi:10.1063/1.373171Garcia, J. ., Asenjo, A., Sinnecker, J. ., & Vazquez, M. (2000). Correlation between GMI effect and domain structure in electrodeposited Co–P tubes. Journal of Magnetism and Magnetic Materials, 215-216, 352-354. doi:10.1016/s0304-8853(00)00156-6Kurlyandskaya, G. V., Barandiarán, J. M., Gutiérrez, J., Garcı́a, D., Vázquez, M., & Vas’kovskiy, V. O. (1999). Magnetoimpedance effect in CoFeNi plated wire with ac field annealing destabilized domain structure. Journal of Applied Physics, 85(8), 5438-5440. doi:10.1063/1.369968Iida, S., Ishii, O., & Kambe, S. (1998). Magnetic Sensor Using Second Harmonic Change in Magneto-Impedance Effect. Japanese Journal of Applied Physics, 37(Part 2, No. 7B), L869-L871. doi:10.1143/jjap.37.l86

Test of the electronic structure of Fe(100) by absorbed current spectroscopy

The absorbed electron current for a clean Fe(100) surface as a function of energy rises step-like at the vacuum-energy cutoff with an absorption close to 1. The smooth decrease of absorbed current at higher electron energy due to secondary electron emission is superimposed by a considerable amount of fine structure, the amplitude of which decreases with increasing energy. These features are found in good agreement with the results of a calculation of the elastic part of the electron reflection coefficient. Further, they are compared with the ferromagnetic electronic bulk bandstructure calculated above the vacuum energy. From the comparison with the experimental data, the energy dependence of the real and imaginary parts of the inner potential is determined

Glassy dynamics and aging in an exactly solvable spin model

We introduce a simple two-dimensional spin model with short-range interactions which shows glassy behavior despite a Hamiltonian which is completely homogeneous and possesses no randomness. We solve exactly for both the static partition function of the model and the distribution of energy barriers, giving us the equilibration time-scales at low temperature. Simulations of instantaneous quenches and of annealing of the model are in good agreement with the analytic calculations. We also measure the two-time spin correlation as a function of waiting time, and show that the model has aging behavior consistent with the distribution of barrier heights. The model appears to have no sharp glass transition. Instead, it falls out of equilibrium at a temperature which decreases logarithmically as a function of the cooling time.Comment: 16 pages, 4 postscript figures, typeset in LaTeX using the RevTeX macro packag

Real space application of the mean-field description of spin glass dynamics

The out of equilibrium dynamics of finite dimensional spin glasses is considered from a point of view going beyond the standard `mean-field theory' versus `droplet picture' debate of the last decades. The main predictions of both theories concerning the spin glass dynamics are discussed. It is shown, in particular, that predictions originating from mean-field ideas concerning the violations of the fluctuation-dissipation theorem apply quantitatively, provided one properly takes into account the role of the spin glass coherence length which plays a central role in the droplet picture. Dynamics in a uniform magnetic field is also briefly discussed.Comment: 4 pages, 4 eps figures. v2: published versio