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Séminaire « Magnétisme et Physique du spin »

Toggling between antiferromagnetism and ferromagnetism with an electric field, just above room temperature - V. Ivanovskaya - Magnetic order and magnetization dynamics in FeRh-based systems : resonant scattering studies using synchrotron and HHG x-ray sources - M. Sacchi - 9 octobre 2014 à 10 h 30

Double séminaire
Jeudi 09 octobre à 10h30 - INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-32 - 4e étage, salle 407

Toggling between antiferromagnetism and ferromagnetism with an electric field,just above room temperature
V. Ivanovskaya - Unité Mixte de Physique CNRS / Thales

Abstract
Controlling magnetism by electric fields is a key issue for the future development of low-power spintronics. Progress has been made in the electrical control of magnetic anisotropy, domain structure, spin polarization or critical temperatures. However, the ability to turn on and off robust ferromagnetism at room temperature and above has been remained elusive until lately. Very recently it has been found that in FeRh/BaTiO3 a moderate electric field can produce a giant magnetization variation [1], arising from the electric-field induced transformation from an antiferromagnetic state to a ferromagnetic FeRh state. The effect occurs just above room temperature and it is mostly driven by voltage-induced strain effects from BaTiO3 but charge accumulation and depletion effects related to the ferroelectric polarization of BaTiO3 possibly contribute as well. In this presentation we will provide a detailed analysis of the obtained experimental data in the light of first-principles calculations. We demonstrate how the magnetic behaviour of the FeRh/BaTiO3 heterostructures can be essentially derived by general considerations on bulk properties of the FeRh system and their evolution with strain and field-effect induced by BaTiO3. More generally, our results suggest new routes to engineer giant magnetoelectric effects by harnessing magnetic phase transitions in transition metal alloys. [1] R. O. Cherifi, V. Ivanovskaya et al, Nature Materials 13, 345–351 (2014).

Magnetic order and magnetization dynamics in FeRh-based systems : resonant scattering studies using synchrotron and HHG x-ray sources
M. Sacchi - INSP

Abstract
The details of the 370 K magneto-structural transition in FeRh are sensitive to the composition, to the strain and, in thin films, to the thickness, and can be modified by applying an external electric or magnetic field. Coupling to a FM overlayer and lateral confinement are two more parameters that can widen the potential of this material for applications. We used resonant scattering of polarized x-rays to investigate the magnetic properties of FeRh thin films, addressing the coupling to a Co overlayer and the role of lateral nano-structuring. Concerning dynamics, we tried to disentangle the sublattices inter-play, which shows a different Fe and Rh response in the fast demagnetization that follows a laser pulse. X-ray scattering techniques provide magnetic measurements with element selectivity, a large probing depth, and imperviousness to applied fields ; being based on x-ray scattering, they can provide (magneto-)structural information as well. First results will be presented, obtained using, as the x-ray source, either synchrotron radiation or laser-induced high-harmonic generation in gases.