Modulating the phase transition temperature of giant magnetocaloric thin films by ion irradiation

Magnetic refrigeration based on the magnetocaloric effect at room temperature is one of the most attractive alternative to the current gas compression/expansion method routinely employed. Nevertheless, in giant magnetocaloric materials, optimal refrigeration is restricted to the narrow temperature window of the phase transition (Tc). In this work, we present the possibility of varying this transition temperature into a same giant magnetocaloric material by ion irradiation. We demonstrate that the transition temperature of iron rhodium thin films can be tuned by the bombardment of ions of Ne 5+ with varying fluences up to 10 14 ions cm --2 , leading to optimal refrigeration over a large 270--380 K temperature window. The Tc modification is found to be due to the ion-induced disorder and to the density of new point-like defects. The variation of the phase transition temperature with the number of incident ions opens new perspectives in the conception of devices using giant magnetocaloric materials

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

Magnetic properties changes of MnAs thin films irradiated with highly charged ions

We present the first investigation on the effect of highly charged ion bombardment on a manganese arsenide thin film. The MnAs films, 150 nm thick, are irradiated with 90 keV Ne$^{9+}$ ions with a dose varying from $1.6\times10^{12}$ to $1.6\times10^{15}$ ions/cm$^2$. The structural and magnetic properties of the film after irradiation are investigated using different techniques, namely, X-ray diffraction, magneto-optic Kerr effect and magnetic force microscope. Preliminary results are presented. From the study of the lattice spacing, we measure a change on the film structure that depends on the received dose, similarly to previous studies with other materials. Investigations on the surface show a strong modification of its magnetic properties

Metastable tetragonal structure of Fe100-xGax epitaxial thin films on ZnSe/GaAs(001) substrate

International audienceWe investigated by x-ray diffraction the Ga concentration dependences of the structural properties of Fe100-xGax (galfenol) thin films grown on a ZnSe/GaAs(001) substrate, a material known for its high magnetostriction. By molecular beam epitaxy (MBE) we grew a series of (001)-oriented layers without in-plane misorientation, ranging from pure Fe up to x = 29.4% Ga. We find a strong Ga-induced tetragonal distortion that conserves the pristine Fe in-plane lattice parameters for all Ga compositions. Supported by theoretical predictions [R. Wu, J. Appl. Phys. 91, 7358 (2002)], we attribute this unusual tetragonal distortion to short-range ordering of Ga-Ga pairs along the [001]-growth direction. The low-temperature and out-of-equilibrium MBE growth regime tends to stabilize a strong deformed tetragonal phase (up to c/a similar to 1.05 for x similar to 29%). This tetragonal structure is fully released by postgrowth annealing

Growth and magnetic properties of vertically aligned epitaxial CoNi nanowires in (Sr, Ba)TiO3 with diameters in the 1.8-6 nm range

The growth by pulsed laser deposition of fully epitaxial nanocomposites made of CoxNi1-x nanowires (NW) vertically self-assembled in Sr0.5Ba0.5TiO3/SrTiO3(001) layers is reported. The diameter of the wires can be tuned in the 1.8-6 nm range. The composition of the wires can be controlled, with the growth sequence and the fcc crystallographic structure of the wires preserved for Co content up to 78%. The nanocomposite systems obtained display a uniaxial magnetic anisotropy with out-of-plane easy axis as shown through analysis of ferromagnetic resonance measurements. It is shown that the magnitude of the magnetic anisotropy depends sensitively on the structural quality of the nanocomposites.The energy barrier for magnetization reversal scales as the square of the diameter of the NW and reaches 60 for 6 nm diameter, with T amb = 300 K.Fil: Schuler, V.. Universite Pierre et Marie Curie; Francia. Centre National de la Recherche Scientifique; FranciaFil: Milano, Julian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Laboratorio Internacional Franco Argentino en Nanociencias; Argentina. Universite Pierre et Marie Curie; FranciaFil: Coati, A.. Synchrotron Soleil; FranciaFil: Vlad, A.. Synchrotron Soleil; FranciaFil: Sauvage Simkin, M.. Synchrotron Soleil; FranciaFil: Garreau, Y.. Synchrotron Soleil; Francia. Université Paris Diderot - Paris 7; Francia. Centre National de la Recherche Scientifique; FranciaFil: Demaille, D.. Universite Pierre et Marie Curie; Francia. Centre National de la Recherche Scientifique; FranciaFil: Hidki, S.. Universite Pierre et Marie Curie; Francia. Centre National de la Recherche Scientifique; FranciaFil: Novikova, A.. Synchrotron Soleil; FranciaFil: Fonda, E.. Synchrotron Soleil; FranciaFil: Zheng, Y.. Universite Pierre et Marie Curie; Francia. Laboratorio Internacional Franco Argentino en Nanociencias; ArgentinaFil: Vidal, F.. Laboratorio Internacional Franco Argentino en Nanociencias; Argentina. Universite Pierre et Marie Curie; Francia. Centre National de la Recherche Scientifique; Franci

Impacts of highly charged ions as seeds in a magneto-structural phase transition of magnetocaloric thin films

International audienceInvestigation on modifications of structural and magnetic properties of magnetocaloric thin films induced by slow highly charged ions bombardment under well-controlled conditions is presented. The ions induce defects/constraints that facilitate nucleation of one phase with respect to the other in the first-order magnetostructural MnAs, with a consequent suppression of thermal hysteresis, but without any significant perturbation on the other structural and magnetic properties

Valorisation energetique de biomasse aquatique associee a une depollution (phase 2)

CNRS RP 400 (717) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc