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Manipulation des propriétés magnétiques de matériaux à effet magnétocalorique géant par impact d’ions lourds

Sophie Cervera 1
1 INSP-E10 - Agrégats et surfaces sous excitations intenses
INSP - Institut des Nanosciences de Paris
Abstract : This work aims to study the effects of slow heavy ions on giant magnetocaloric materials. These materials present a first order phase transition coupled to a strong variation of entropy (S) potentially exploitable for the development of system of effective magnetic refrigeration. On the other hand, the thermal hysteresis and the small temperature range where S is high, associated to the first order phase transition, restrict the use of these materials. In this work, we used specific effects of the heavy ions interacting with solids to modify their properties: the slow ions induce disorder and point-like defects into materials. In manganese arsenide thin films, presenting a magneto-structural transition, we demonstrated that this new defects act like nucleation centers which make easier the phase change during the transition. This action has enabled to suppress the thermal hysteresis for the first time and in a stable way in time. By varying the mass and the kinetic energyof the ions, we were able to highlight the fundamental role of the density of elastic collisions generated by these irradiations and to rule out the contribution of the implanted ions. In iron-rhodium thin films, another giant magnetocaloric material with a metamagnetic phase transition were also studied. In this case, the thermal hysteresis is not suppressed but rather enlarged by the impact of ions which indicate that the phase structural change play an important role in the process of reduction of thermal hysteresis. Furthermore our investigations demonstrate that by controlling irradiation conditions, in particular the number of incident ions, the temperature of phase transition could be modulated. This effect is a new method to spatially tune, on the same sample, the temperature of phase transition where the magnetocaloric effect is maximal. This method would allow to overcome the narrow range of useful temperature of this type of materials, another parameter criticizes for applications in magnetic refrigeration.
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Sophie Cervera. Manipulation des propriétés magnétiques de matériaux à effet magnétocalorique géant par impact d’ions lourds. Physique Atomique [physics.atom-ph]. Sorbonne Universités, UPMC Univ Paris 06, 2017. Français. ⟨tel-01706419⟩

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