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Li X.,Shanghai University | Li X.,Grenoble Institute of Technology | Gagnoud A.,Grenoble Institute of Technology | Ren Z.,Shanghai University | And 2 more authors.
Journal of Materials Research | Year: 2013

The effect of a strong magnetic field on the solid solubility and the microsegregation during directional solidification of Al-Cu alloy at lower growth speeds (1-10 μm/s) has been investigated experimentally. Results indicate that the magnetic field causes the reduction of the grain boundary and promotes the amalgamation of the grains. Further, measurement results reveal that the magnetic field increases the solid solubility and decreases the microsegregation. It is also found that the value of the solid solubility increases as the magnetic field and the temperature gradient increase. The modification of the solid solubility and the microsegregation under the magnetic field is attributed to the thermoelectric magnetic force acting on the solid and the interdendritic thermoelectric magnetic convection. The present work may initiate a new method to enhance the solid solubility and to eliminate the microsegregation in Al-based alloys via an applied strong magnetic field during directional solidification. © 2013 Materials Research Society.

Jandl S.,Université de Sherbrooke | Mansouri S.,Université de Sherbrooke | Mukhin A.A.,RAS A.M. Prokhorov General Physics Institute | Yu Ivanov V.,RAS A.M. Prokhorov General Physics Institute | And 5 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2011

In DyMnO3 orthorhombic single crystals, the weak Raman active phonon softening below T=100 K is correlated with the study of infrared active Dy3 CF excitations as a function of temperature and under applied magnetic field. We detect five H13/2 CF transitions that we predict with appropriate CF Hamiltonian and we confirm that the magnetic easy axis lies in the ab plane. While the CF energy level shifts below T=100 K reflect different displacements of the oxygen ions that contribute to the phonon softening, lifting of the ground state Kramers doublet degeneracy (∼30 cm-1) is observed below TN=39 K due to the anisotropic Mn3-Dy3 interaction, which could be responsible for the stability of the bc-cycloid ferroelectric phase. © 2011 Elsevier B.V. All rights reserved.

Jandl S.,Université de Sherbrooke | Mansouri S.,Université de Sherbrooke | Vermette J.,Université de Sherbrooke | Mukhin A.A.,RAS A.M. Prokhorov General Physics Institute | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2013

In hexagonal DyMnO3, Dy3+ crystal-field excitations are studied as a function of temperature and applied magnetic field. They are complemented with the measurements of infrared active phonon frequency shifts under applied magnetic field at T = 4.2 K. Between TN = 68 K and T = 10 K, the absence of Dy3+ Kramers doublet splittings at either the C3 or the C3v site symmetries indicates that the Mn 3+ magnetic order effective exchange field has no component parallel to the c-axis at either site. Below T = 10 K, the ground state Kramers doublet splits under the Dy3+ internal effective field as well as the applied magnetic field. Also, relatively strong infrared active phonon energy shifts are observed in magneto-infrared reflectance measurements at T = 4.2 K, allowing the calculation of the induced electric polarization changes as a function of the applied magnetic field. Such changes are associated with a large magnetoelectric effect in DyMnO3, arising from a charge transfer between Dy3+ and apical oxygen ions. © 2013 IOP Publishing Ltd.

Mansouri S.,Université de Sherbrooke | Jandl S.,Université de Sherbrooke | Roberge B.,Université de Sherbrooke | Balli M.,Université de Sherbrooke | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2016

We have studied the Raman and infrared spectral response of TbMn2O5 under an applied magnetic field parallel to the easy magnetic a-axis at 4.2 K. Strong spin-lattice coupling in TbMn2O5 is evidenced by a frequency shift of Raman and infrared phonons as a function of magnetic field compared to the phonon response of BiMn2O5 that remains unaffected. The magnetic field behavior of the highest frequency phonons retraces the polarization switching in TbMn2O5 and shows an important frequency softening below 3 T that is modulated by the J 3 and J 4 exchange parameters. The role of the Tb3+ spin alignment with H is interpreted in terms of a local lattice striction and the contribution of the charge transfer mechanism to the magnetoelectric process is evaluated. © 2016 IOP Publishing Ltd.

Vermette J.,Université de Sherbrooke | Jandl S.,Université de Sherbrooke | Orlita M.,Grenoble High Magnetic Field Laboratory | Gospodinov M.M.,Bulgarian Academy of Science
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Infrared active phonons of HoMnO 3 and LuMnO 3 single crystals are studied under an applied magnetic field below Ho3 + spin ordering at T=4.2 K. Interestingly, relatively strong mode energy shifts, induced by the magnetic field, are observed in HoMnO 3 but are absent in the nonmagnetic rare-earth compound LuMnO 3. We associate the large magnetoelectric effects in HoMnO 3 with a mechanism of charge transfer between Ho3 + and apical oxygen. Also, the exact values of the published polarization change under the applied magnetic field are predicted with no adjustable parameters. © 2012 American Physical Society.

Winnerl S.,Helmholtz Center Dresden | Stehr D.,Helmholtz Center Dresden | Wagner M.,Helmholtz Center Dresden | Schneider H.,Helmholtz Center Dresden | And 18 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

The free-electron laser FELBE at the Helmholtz-Zentrum Dresden Rossendorf enables experiments with spectral, temporal, and, by means of near-field microscopy, also high spatial resolution. FELBE delivers picosecond IR and THz pulses in a wavelength range from 4 μm to 280 μm. Here we review the potential of the laser and focus on two highlight pump-probe experiments. In the first experiment, the relaxation dynamics in self assembled InGaAs quantum dots at energies below the Reststrahlen band is studied. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to ~ 2 ps at 30 meV (7 THz). The results are in very good agreement with our microscopic theory of the carrier relaxation process, taking into account polaron decay via acoustic phonons. In the second experiment, the relaxation dynamics in graphene is investigated at photon energies E = 20 - 250 meV. For excitations below the energy of the optical phonon (G mode), the relaxation times are more than one order of magnitude longer as compared to the relaxation times observed for near infrared excitation. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Builles N.,Banque de Cornees des Hospices Civils de Lyon | Janin-Manificat H.,Banque de Cornees des Hospices Civils de Lyon | Malbouyres M.,University of Lyon | Justin V.,Banque de Cornees des Hospices Civils de Lyon | And 10 more authors.
Biomaterials | Year: 2010

We recently showed that the highly organized architecture of the corneal stroma could be reproduced using scaffolds consisting of orthogonally aligned multilayers of collagen fibrils prepared using a high magnetic field. Here we show that such scaffolds permit the reconstruction in vitro of human hemi-corneas (stroma + epithelium), using primary human keratocytes and limbal stem cell derived human keratinocytes. On the surface of these hemi-corneas, a well-differentiated epithelium was formed, as determined both histologically and ultrastructurally and by the expression of characteristic markers. Within the stroma, the keratocytes aligned with the directions of the fibrils in the scaffold and synthesized a new extracellular matrix with typical collagen markers and small, uniform diameter fibrils. Finally, in vivo experiments using a rabbit model showed that these orthogonally oriented multi-layer scaffolds could be used to repair the anterior region of the stroma, leading to re-epithelialization and recovery of both transparency and ultrastructural organization. © 2010 Elsevier Ltd.

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