Structure and magnetism of orthorhombic epitaxial FeMnAs

The molecular beam epitaxy growth of Fe on MnAs/GaAs(001) leads to the formation of an epitaxial FeMnAs phase at the Fe/MnAs interface. The investigation of the structure by high angle annular dark field imaging in a scanning transmission electron microscope reveals an unusual orthorhombic structure, with vacancy ordering. Ab initio calculations show an antiferromagnetic ground state for this orthorhombic FeMnAs.Fil: Demaille, Dominique. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; FranciaFil: Patriarche, Gilles. Centre National de la Recherche Scientifique; FranciaFil: Helman, Christian. Comisión Nacional de Energía Atómica; Argentina. Laboratorio Internacional Franco-Argentino en Nanociencias; FranciaFil: Eddrief, Mahmoud. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; FranciaFil: Etgens, Hugo. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; FranciaFil: Sacchi, Maurizio. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; Francia. L’Orme des merisiers Saint-Aubin. Synchrotron SOLEIL; FranciaFil: Llois, Ana Maria. Comisión Nacional de Energía Atómica; Argentina. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Marangolo, Massimiliano. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; Franci

Suppression of the thermal hysteresis in magnetocaloric MnAs thin film by highly charged ion bombardment

We present the investigation on the modifications of structural and magnetic properties of MnAs thin film epitaxially grown on GaAs induced by slow highly charged ions bombardment under well-controlled conditions. The ion-induced defects facilitate the nucleation of one phase with respect to the other in the first-order magneto-structural MnAs transition with a consequent suppression of thermal hysteresis without any significant perturbation on the other structural and magnetic properties. In particular, the irradiated film keeps the giant magnetocaloric effect at room temperature opening new perspective on magnetic refrigeration technology for everyday use

Fe-induced spin-polarized electronic states in a realistic semiconductor tunnel barrier

International audienceWhenever iron is grown on Zn-terminated ZnSe(001) substrates, the most stable configurations of Fe/ZnSe(001) magnetic tunnel junctions show Fe-Se bonding and include a Fe-Zn intermixed interface layer, as suggested by spectroscopic measurement and confirmed here by calculations based on the density functional theory. The presence of the intermixed Fe-Zn layer at the junction strongly reduces the spin polarization of both the interface and metal-induced gap states within the ZnSe tunnel barrier

Measurement of thermal properties of bulk materials and thin films by modulated thermoreflectance (MTR)

International audienceThermal conductivity and thermal diffusivity of materials must be known at high accuracy for thermal engineering applications, in order to understand energy dissipation in devices and engines. Thermal conductivity libraries can be unreliable since their reported values may not reflect the complexities of the samples under investigation, and new materials may not yet be listed. Over the past three decades, modulated thermoreflectance (MTR) has emerged and evolved as a reliable, non-contact, and noninvasive technique to measure the thermal properties of a wide range of bulk and thin film materials and their interfaces. This Tutorial discusses the basis of, and recent advances in, the MTR technique, and its applications in the thermal characterization of a variety of materials. MTR experiments use two micrometer-wide laser beams. Experimental data (amplitude and phase vs the offset between the pump and the probe) give information about heat diffusion around the heat source along several tens of micrometers. Heat diffusion equations are used to fit the experimental data and extract the required thermal properties. Importantly, best fit procedures are not always needed because some analytical approximations provide evidence of the required thermal properties. We present many examples (bulk materials, layered sample, etc.) which illustrate this

Finite-Element Modeling of Thermoelastic Attenuation in Piezoelectric Surface Acoustic Wave Devices

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Magnetocrystalline and magnetoelastic constants determined by magnetization dynamics under static strain

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Surface structures of MnAs grown on GaAs (111)-B substrates.

Atomically flat MnAs epilayers grown on GaAs(111)B substrates by molecular-beam epitaxy present surface structures depending on the sample temperature and on the surface stoichiometry: the known (2×2) reconstruction and two new phases, i.e., a (3×1) reconstruction and a mixed phase of (2×2) and (3×1). By monitoring the reflection high-energy electron-diffraction diagram evolution as a function of the annealing temperature, it was possible to ascribe the (3×1) as being the As richest phase and the (2×2) as the As poorest phase. Two structural models for the observed reconstructions [i.e., (3×1) and (2×2)] are proposed