The influence of phosphorus content on magnetic anisotropy in ferromagnetic (Ga, Mn) (As, P)/GaAs thin films

International audienceThe magnetic anisotropy of the ferromagnetic semiconductor (Ga, Mn) (As, P) is studied in a material-specific microscopic k . p approach. We calculate the electronic energy band structure of (Ga, Mn) (As, P) quaternary ferromagnetic alloys using a 40-band k . p model and taking into account the s, p-d exchange interaction and the strain of the (Ga, Mn) (As, P) layer on a GaAs substrate. We determine the variations of the carrier effective masses in the strained (Ga, Mn) (As, P)/GaAs system. The magnetic anisotropy constants obtained from our simulations using a mean-field model are compared with the experimental ones determined by ferromagnetic resonance spectroscopy on a set of samples with constant manganese concentration and varying phosphorus concentration. An excellent quantitative agreement between experiment and theory is found for the uniaxial out-of-plane and cubic in-plane anisotropy parameters

Structural and magnetic properties of molecular beam epitaxy (MnSb2Te4)x(Sb2Te3)1-x topological materials with exceedingly high Curie temperature

Tuning magnetic properties of magnetic topological materials is of interest to realize elusive physical phenomena such as quantum anomalous hall effect (QAHE) at higher temperatures and design topological spintronic devices. However, current topological materials exhibit Curie temperature (TC) values far below room temperature. In recent years, significant progress has been made to control and optimize TC, particularly through defect engineering of these structures. Most recently we showed evidence of TC values up to 80K for (MnSb2Te4)x(Sb2Te3)1-x, where x is greater than or equal to 0.7 and less than or equal to 0.85, by controlling the compositions and Mn content in these structures. Here we show further enhancement of the TC, as high as 100K, by maintaining high Mn content and reducing the growth rate from 0.9 nm/min to 0.5 nm/min. Derivative curves reveal the presence of two TC components contributing to the overall value and propose TC1 and TC2 have distinct origins: excess Mn in SLs and Mn in Sb2-yMnyTe3QLs alloys, respectively. In pursuit of elucidating the mechanisms promoting higher Curie temperature values in this system, we show evidence of structural disorder where Mn is occupying not only Sb sites but also Te sites, providing evidence of significant excess Mn and a new crystal structure:(Mn1+ySb2-yTe4)x(Sb2-yMnyTe3)1-x. Our work shows progress in understanding how to control magnetic defects to enhance desired magnetic properties and the mechanism promoting these high TC in magnetic topological materials such as (Mn1+ySb2-yTe4)x(Sb2-yMnyTe3)1-x

Emission State Structure and Linewidth Broadening Mechanisms in Type-II CdSe/CdTe Core–Crown Nanoplatelets: A Combined Theoretical–Single Nanocrystal Optical Study

Type-II heterostructures are key elementary components in optoelectronic, photovoltaic, and quantum devices. The staggered band alignment of materials leads to the stabilization of indirect excitons (IXs), i.e., correlated electron–hole pairs experiencing spatial separation with novel properties, boosting optical gain and promoting strategies for the design of information storage, charge separation, or qubit manipulation devices. Planar colloidal CdSe/CdTe core–crown type-II nested structures, grown as nanoplatelets (NPLs), are the focus of the present work. By combining low temperature single NPL measurements and electronic structure calculations, we gain insights into the mechanisms impacting the emission properties. We are able to probe the sensitivity of the elementary excitations (IXs, trions) with respect to the appropriate structural parameter (core size). Neutral IXs, with binding energies reaching 50 meV, are shown to dominate the highly structured single NPL emission. The large broadening linewidth that persists at the single NPL level clearly results from strong exciton–LO phonon coupling (Eph = 21 meV) whose strength is poorly influenced by trapped charges. The spectral jumps (≈10 meV) in the photoluminescence recorded as a function of time are explained by the fluctuations in the IX electrostatic environment considering fractional variations (≈0.2 e) of the noncompensated charge defects

Stabilité des ostéosynthèses biorésorbables dans la chirurgie orthognathique des classes III (à propos de 30 cas)

Le but de cette étude est d'évaluer la stabilité des ostéotomies bimaxillaires pour la correction des malocclusions de type classe III dont l'ostéosynthèse est réalisée à l'aide de matériel bio résorbable. 30 patients ont bénéficiés d'une telle synthèse lors du traitement qui consistait en une ostéotomie sagittale des branches montantes de recul mandibulaire associée à une ostéotomie de Le Fort I d'avancée du maxillaire. Des téléradiographies de profil ont été réalisées en pré-opératoire (T0), post-opératoire immédiat (T1), et en post-opératoire tardif (T2). Les analyses céphalométriques ont été menées selon la méthode de DELAIRE. Un repère orthonormé à partir des lignes C1 et C0 a permis le recueil des coordonnées des points squelettiques choisis. La stabilité des résultats est analysée aux différents temps, en fonction les changements sagittaux, verticaux et les modifications angulaires. Les résultats confirment la stabilité occlusale mais également la qualité esthétique et fonctionnelle des résultats. Même si des déplacements osseux et dentaires sont constatés, comme dans la plupart des séries analysées dans la littérature, ils sont négligeable et sans conséquence sur la qualité du résultat final. Les caractéristiques de ce type de synthèse, à mi-chemin entre les synthèses souples et rigides, permettent une adaptation fonctionnelle des sites d'ostéotomies au nouvel équilibre facial, cela facilite les ajustements orthodontiques post-opératoires et participe au confort global du patient. Leur résorption laisse place à une restauration osseuse ad integrum et le patient n'a pas à supporter de deuxième intervention pour la dépose du matériel. Le matériel biorésorbable est donc parfaitement justifié en chirurgie orthognathique. Reste la question de la place qu'il va prendre progressivement dans tous les domaines de la chirurgie cranio-maxillo-faciale. Des progrès sont toutefois à attendre tant dans le sens d'une amélioration de leurs caractéristiques biomécaniques que dans celui de la création de produits développés grâce à l'ingénierie tissulaire.AMIENS-BU Santé (800212102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Interaction hyperfine spin du trou-spin des noyaux dans les boites quantiques d InAs/GaAs

PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Nuclear field effect on the spin dynamics of electron localized on a donor in a single quantum well

International audienceWe use photoinduced Faraday rotation (PFR) in presence of an applied magnetic field to study the spin dynamics of localized electrons. The sample is a CdTe/CdMgTe quantum well (QW) of width 80 angstrom containing a layer of iodine donors at its center, with, concentration 10(11) cm(-2). The spin polarization of donor bound electrons is built via the optical polarization of donor-bound excitons, their hole spin relaxation, and their recombination. In a transverse (in-plane) magnetic field, PFR shows damped Larmor oscillations from which we deduce a 18 ns electron-spin decoherence time, and a transverse Lande factor of 1.29. In addition, for oblique optical incidence the electron-nuclei hyperfine interaction builds a nuclear spin polarization in presence of polarized electrons. This leads to the construction of an effective magnetic field, the Overhauser field, acting on the electronic spins. The Larmor frequency is then different for sigma+ or sigma- polarizations of the exciting light. The dependence of the phenomenon on the optical incidence allows the determination of the maximal Overhauser field, which is about 10mT, at least two orders of magnitude weaker than for III-V semiconductors. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The so-called ``Trion line'': A singular many-body effect between one composite exciton and many electrons

International audienceAlthough commonly called ``trion line'', the low-energy line observed in the absorption spectrum of doped quantum wells, is not due to a bound 3-body object, the trion. In fact, it comes from a many-body object, spectrally wide by nature, made of one composite exciton and a large number of electrons, interacting through both Coulomb and Pauli scatterings, i.e., Coulomb interaction without carriers exchange, and carriers exchange without Coulomb process. This understanding is experimentally supported by the highly asymmetrical shape of the circular dichroism spectrum measured with a spin-polarized electron gas: this spectrum shows a sharp edge at low energy and a long tail a high energy, which are well explained by a singular many-body effect, while they completely rule out an explanation in terms of trion, either free or bound

(Ga,Mn)As layers with perpendicular anisotropy: a study of magnetic domain patterns

International audienceThe magnetic domain pattern in (Ga,Mn)As layers with perpendicular magnetic easy-axis is studied by Kerr microscopy at various temperatures. We investigate the effect of post-growth annealing. As-grown samples exhibit a strongly anisotropic domain growth with dendritic-like expansion of domains along the directions. For annealed samples, the density of nucleation centers is decreased and domain wall propagation is more isotropic. Two kinds of pinning centers are observed in annealed samples: line-like defects that strongly hinder domain wall propagation and point-like defects with a density of a few 10(5) cm(-2)

Magnetic domain patterns in as-grown and annealed (Ga,Mn)As epilayers with perpendicular easy axis

International audienceMagnetic properties of ferromagnetic (GaMn)As epilayers grown with tensile strain are investigated using combined experimental techniques including Kerr microscopy, transport measurements, and SQUID magnetometry. We show that post-growth annealing substantially increases the Curie temperature, strengthens the perpendicular anisotropy, weakens the in-plane anisotropy and drastically changes the magnetic domain pattern