Magnetic Ordering Of Eutepbte Multilayers Determined By X-ray Resonant Diffraction

In this work we use resonant x-ray diffraction combined with polarization analysis of the diffracted beam to study the magnetic ordering in EuTePbTe multilayers. The presence of satellites at the (1/2 1/2 1/2) magnetic reflection of a 50 repetition EuTePbTe superlattice demonstrated the existence of magnetic correlations among the alternated EuTe layers. The behavior of the satellites intensity as T increases toward the Ǹel temperature TN indicates that these correlations persist nearly up to TN and suggests the preferential decrease of the magnetic order parameter of external monolayers of each EuTe layer within the superlattice. © 2008 American Institute of Physics.9224Lovesey, S.W., Collins, S.P., (1996) X-Ray Scattering and Absorption by Magnetic Materials, , (Oxford University Press, New York)Granado, E., Pagliuso, P.G., Giles, C., Lora-Serrano, R., Yokaichiya, F., Sarrao, J.L., (2004) Phys. Rev. B, 69, p. 144411. , PRBMDO 0163-1829 10.1103/PhysRevB.69.144411Tonnerre, J.M., Seve, L., Raoux, D., Rodmacq, B., De Santis, M., Troussel, P., Brot, J.M., Chen, C.T., (1995) Nucl. Instrum. Methods Phys. Res. B, 97, p. 444. , NIMBEU 0168-583X 10.1016/0168-583X(94)00721-7Langridge, S., Stirling, W.G., Lander, G.H., Rebizant, J., (1994) Phys. Rev. B, 49, p. 12010. , PRBMDO 0163-1829 10.1103/PhysRevB.49.12010Leiner, V., Ay, M., Zabel, H., (2004) Phys. Rev. B, 70, p. 104429. , PRBMDO 0163-1829 10.1103/PhysRevB.70.104429Kepa, H., Springholz, G., Giebultowicz, T.M., Goldman, K.I., Majkrzak, C.F., Kacman, P., Blinowski, J., Bauer, G., (2003) Phys. Rev. B, 68, p. 024419. , PRBMDO 0163-1829 10.1103/PhysRevB.68.024419Binder, K., Hohenberg, P.C., (1974) Phys. Rev. B, 9, p. 2194. , PLRBAQ 0556-2805 10.1103/PhysRevB.9.2194Oliveira, N.F., Foner, S., Shapira, Y., Reed, T.B., (1972) Phys. Rev. B, 5, p. 2634. , PLRBAQ 0556-2805 10.1103/PhysRevB.5.2634Giles, C., Yokaichiya, F., Kycia, S.W., Sampaio, L.C., Ardiles-Saravia, D.C., Franco, M.K.K., Neuenschwander, R.T., (2003) J. Synchrotron Radiat., 10, p. 430. , JSYRES 0909-0495 10.1107/S0909049503020958Hol, V., Kubena, J., Ploog, K., (1990) Phys. Status Solidi B, 162, p. 347. , PSSBBD 0370-1972 10.1002/pssb.2221620204Nunez, V., Majkrzak, C.F., Springholz, G., Bauer, G., Giebultowicz, T.M., Kepa, H., Goldman, K.I., (1998) Superlattices Microstruct., 23, p. 41. , SUMIEK 0749-6036 10.1006/spmi.1996.0205Giebultowicz, T.M., Kepa, H., Blinowski, J., Kacman, P., (2001) Physica e (Amsterdam), 10, p. 411. , PELNFM 1386-9477 10.1016/S1386-9477(01)00128-

Sharp lines in the absorption edge of EuTe and Pb0.1_{0.1}Eu0.9_{0.9}Te in high magnetic fields

The optical absorption spectra in the region of the \fd transition energies of epitaxial layers of of EuTe and \PbEuTe, grown by molecular beam epitaxy, were studied using circularly polarized light, in the Faraday configuration. Under \sigmam polarization a sharp symmetric absorption line (full width at half-maximum 0.041 eV) emerges at the low energy side of the band-edge absorption, for magnetic fields intensities greater than 6 T. The absorption line shows a huge red shift (35 meV/T) with increasing magnetic fields. The peak position of the absorption line as a function of magnetic field is dominated by the {\em d-f} exchange interaction of the excited electron and the \Euion spins in the lattice. The {\em d-f} exchange interaction energy was estimated to be $J_{df}S=0.15\pm 0.01$ eV. In \PbEuTe the same absorption line is detected, but it is broader, due to alloy disorder, indicating that the excitation is localized within a finite radius. From a comparison of the absorption spectra in EuTe and \PbEuTe the characteristic radius of the excitation is estimated to be $\sim 10$\AA.Comment: Journal of Physics: Condensed Matter (2004, at press

Measurement of miniband parameters of a doped superlattice by photoluminescence in high magnetic fields

We have studied a 50/50\AA superlattice of GaAs/Al$_{0.21}$Ga$_{0.79}$As composition, modulation-doped with Si, to produce $n=1.4\times 10^{12}$ cm$^{-2}$ electrons per superlattice period. The modulation-doping was tailored to avoid the formation of Tamm states, and photoluminescence due to interband transitions from extended superlattice states was detected. By studying the effects of a quantizing magnetic field on the superlattice photoluminescence, the miniband energy width, the reduced effective mass of the electron-hole pair, and the band gap renormalization could be deduced.Comment: minor typing errors (minus sign in eq. (5)

Monte Carlo Simulation of Epitaxial Growth

A numerical Monte Carlo (MC) model is described in detail to simulate epitaxial growth. This model allows the formation of structural defects, like substitutional defects and vacancies, and desorption of adsorbed atoms on the surface. The latter feature supports the study of epitaxial growth at very high kinetic regime. The model proposed here is applied to simulate the homoepitaxial growth of Si. The results obtained fit well to the experimental reports on (0 0 1) silicon homoepitaxy. The easy implementation of a large number of microscopic processes and the three-dimensional spatial information during the film growth suggests that the model can be applied to simulate the growth of binary, ternary, or more compounds and even the growth of superlattices and heterostructures

Magnetic ordering of EuTe/PbTe multilayers determined by x-ray resonant diffraction

In this work we use resonant x-ray diffraction combined with polarization analysis of the diffracted beam to study the magnetic ordering in EuTe/PbTe multilayers. The presence of satellites at the (1/2 1/2 1/2) magnetic reflection of a 50 /repetition EuTe/PbTe superlattice demonstrated the existence of magnetic correlations among the alternated EuTe layers. The behavior of the satellites intensity as T increases toward the Neel temperature T(N) indicates that these correlations persist nearly up to T(N) and suggests the preferential decrease of the magnetic order parameter of external monolayers of each EuTe layer within the superlattice. (C) 2008 American Institute of Physics.922