Thèses

Lundi 22 Mai 2023 à 14h00.

Structure and magnetism of B2 chemically ordered FeRh nanoclusters in carbon matrix, as a nanocluster assembled film and over pevoskite substrate

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Directeur de thèse / thesis director : DUPUIS Véronique / CAÑERO INFANTE Ingrid

Membres du jury / jury members :
ANDREAZZA Pascal
BARTHELEMY Agnès
COTTANCIN Emmanuel
MAGNAN Hélène
PICCOLO Laurent
RESPAUD Marc

Résumé / Abstract :
Controlling nanomagnetism by means of an electric field is a key issue for the future development of low-power spintronic. In this context, near equiatomic composition, the CsCl-like B2 chemically ordered FeRh alloy which presents a metamagnetic transition from a low temperature antiferromagnetic order to a high temperature ferromagnetic order just above room temperature, is a very good candidate for assessing magnetic control through external stimuli. Recently, a ferroelectric crystal has been used to electrically drive the temperature of such metamagnetic phase transition (MPT) of epitaxially grown FeRh films with only a few volts, with potential media applications for thermally assisted magnetic recording. This effect may be the signature of magnetic exchange correlations, acting at shorter-range in the AF than in the FM phases.

In order to achieve a better understanding and control of such metamagnetic phase transition, we have explored the finite size effect in multiferroic heterostructure at the ultimate nanoscale. Thus monodomain FeRh nanomagnets have been prepared by low energy clusters beam deposition with different sizes. We have studied structure and magnetism of B2 chemically ordered FeRh nanoclusters in carbon matrix, as a nanocluster assembled film and over pevoskite substrate. In a first step, we have shown that annealing at high temperature under vacuum allow to reach the B2 chemical order for every studied system. We evidence an intrinsic critical nanosize for the observation of the metamagnetic AF/FM transition with the coexistence of several magnetic orders by studing also the role of of interaction in nanogrunular systems. By using X-ray spectroscopy and diffraction under synchrotron facilities, we well-describe epitaxial relationship between faces of alloy nanocristal and surface of SrTiO3 et BaTiO3 substrates, by showing that competition between induced strain at the Metal/Oxide interface and cluster surface relaxation avoid to induce antiferromagnetic order in nanoparticles.

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