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-

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

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)

Magnetic ordering and transitions of EuSe studied by x-ray diffraction

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The magnetic phase diagram and thermal expansion of EuSe is revisited using a high-quality 3200-angstrom-thick epitaxial film grown over a (111)BaF(2) substrate. Resonant magnetic x-ray diffraction experiments reveal a highly hysteretic magnetic phase diagram between 1.8 and T(N)similar to 4.7 K, in which two antiferromagnetic phases with propagation vectors (k) over right arrow (I)=[(1)/(4), (1)/(4),-(1)/(4)] (represented by up arrow up arrow down arrow down arrow) and (k) over right arrow (II)=[(1)/(2),(1)/(2),-(1)/(2)](up down arrow up down arrow) are observed. In addition, a defective phase with (k) over right arrow (III)=[h, h, -h]((1)/(4)<h<(1)/(3)) competes with the up arrow up arrow down arrow down arrow phase. Details of the temperature dependence of (k) over right arrow (III) and corresponding peak widths indicate this phase is intermediate between up arrow up arrow down arrow down arrow (h=(1)/(4)) and an ideal ferrimagnetic up arrow up arrow down arrow phase (h=(1)/(3)), and may be represented by (n x up arrow up arrow down arrow+down arrow), with mean n values between 7 and 2. High-resolution x-ray diffraction experiments show unit-cell hysteretic distortions that correlate with the transitions to the different magnetic phases existing below T(N).8118Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Plasma Ion Implantation of Nitrogen into Silicon: High Resolution X-ray Di raction

In the present study we use x-ray di raction methods to characterize the surface of Si wafers irradiated with nitrogen by Plasma Immersion Ion Implantation. This is a non-line-of-sight ion implantation method, which allows three-dimensional treatment of materials including semiconductors, metals and dielectrics. The atomic concentration pro les in the implanted Si wafers were measured by Auger electron spectroscopy. The 004 Si rocking curve !-scan was measured in a high resolution x-ray di ractometer equipped with a Ge220 four-crystal monochromator before and after implantation. A distortion of the Si 004-rocking curve w as clearly observed for the as-implanted sample. This rocking curve w as successfully simulated by dynamical theory of x-ray di raction, assuming a Gaussian strain pro le through the implanted region. The analysis made by x-ray di raction and Auger electron spectroscopy revealed successful implantation of ions with accumulated nitrogen dose of 1:510 17 cm ,3 . The Siwafers can be used as high sensitivity monitors in the Plasma Immersion Ion Implantation process, especially at the low dose range. I Introduction Plasma Immersion Ion Implantation PIII is a novel ion implantation technique developed recently for the improvement of the surface properties of materials including semiconductors, metals and dielectrics 1 . It is inherently a non-line-of-sight ion implantation method which allows three-dimensional surface treatment o f manufactured workpieces of large dimension and or complex shapes, at high speed, in batch processing mode and in a cost-e ective manner 2 . In PIII, the ions of interest are extracted directly from the plasma in which the samples to be processed are immersed, without the need of acceleration grids. In this work, Siwafers were implanted with nitrogen using the PIII technique. The wafers were characterized by Auger Electron Spectroscopy AES in order to determine the concentration pro les. The samples were analyzed by high-resolution x-ray di raction before and after implantation. The pro les of the Si 004 rocking curves were simulated by dynamical theory of x-ray di raction and compared with the measured data. II Plasma Immersion Ion Implantation Syste

Structural And Magnetic Characterization Of Eute/snte Superlattices Grown By Molecular Beam Epitaxy

Here we investigate the structural and magnetic properties of 24 repetitions EuTe/SnTe superlattices (SLs), with 3 monolayers (ML) EuTe films and SnTe thicknesses between 13 and 36 ML. The SLs were grown by molecular beam epitaxy on 3 μm SnTe buffer layers, grown on top of (111)BaF2 substrates. High resolution x-ray diffraction measurements indicated that the SLs with thicker SnTe layers have higher structural quality. This is due to the SnTe growth mode on EuTe, which starts in islands and evolves to layer-by-layer. The magnetic diffraction peak observed for the higher quality SLs proved the existence of antiferromagnetic order within the individual EuTe layers. Decreasing the width of the non-magnetic SnTe layers resulted in rougher interfaces, and the fading of the magnetic peak signal. The magnetization versus applied field curves indicated that the magnetic moments of SLs with thinner SnTe layers were also harder to align along the field direction. We interpret our results considering the loss of Eu neighbors, related with the increasing roughness of the SL interfaces. © 2009 American Institute of Physics.1199157158Kepa, H., (2003) Phys. Rev. B, 68, p. 024419Blinowski, J., Kacman, P., (2001) Phys. Rev. B, 64, p. 045302Oliveira, N.F., Foner, S., Shapira, Y., Reed, T.B., (1972) Phys. Rev. B, 5, p. 2634Díaz, B., (2008) Appl. Phys. Lett, 92, p. 242511Díaz, B., Rappl, P.H.O., Abramof, E., (2007) J. Cryst. Growth, 308, p. 218Holý, V., Kubena, J., Ploog, K., (1990) Phys. Status Solidi B, 162, p. 347Giles, C., (2003) J. Synchrotron Rad, 10, p. 43

Spin-induced optical second harmonic generation in the centrosymmetric magnetic semiconductors EuTe and EuSe

Spectroscopy of the centrosymmetric magnetic semiconductors EuTe and EuSe reveals spin-induced optical second harmonic generation (SHG) in the band gap vicinity at 2.1-2.4eV. The magnetic field and temperature dependence demonstrates that the SHG arises from the bulk of the materials due to a novel type of nonlinear optical susceptibility caused by the magnetic dipole contribution combined with spontaneous or induced magnetization. This spin-induced susceptibility opens access to a wide class of centrosymmetric systems by harmonics generation spectroscopy.Comment: 5 pages, 3 figures, submitted to PR