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Domain wall dynamics driven by spin-current in ferrimagnetic alloys

Abstract : Despite the large success of spintronics, several questions remain concerning the improvement of efficiency and speed of the magnetization manipulation by electrical current. Those issues can be addressed through the study of new exotic materials that mix different magnetic sub-lattices. Rare earth-transition metal ferrimagnetic alloys are composed of two different magnetic sub-lattices that are antiferromagneticaly coupled. Specifically, two interesting configurations can emerge called the magnetic and the angular compensation points at which the alloy’s net magnetization or net angular momentum independently vanishes. In these configurations, ferrimagnets seem to present new and very convenient properties which makes them promising for both fundamental and technological point of view. In this thesis, these materials were experimentally and theoretically studied through the prism of magnetic domain wall dynamics driven by spin-currents.Ferrimagnetic alloys (such as TbFeCo or GdFeCo) were grown in thin films by co-evaporation. Their structural and magnetic properties were studied by combining magnetization, electrical and optical methods which have revealed their spintronic value. Imaging techniques showed a perpendicularly magnetized domain organization separated by easily handled domain walls. These statics properties studies also showed a chemical depth gradient which induces surface-like effects in the bulk region of films such as DMI à définir.The domain wall dynamics driven by spin current were investigated in two studies revealing very high efficiency and speed of their electrical manipulation. First, the efficiency of the current manipulation via spin-transfer torque was measured by studying the domain wall motion under combined effects of field and current in the creep regime. Secondly, the domain wall dynamics driven by spin-orbit torque was fully characterized using in-plane fields. This measurement revealed a singular dynamic of the domain wall at the angular compensation point which is the direct signature of the precession-free reversal of the magnetization.Finally, an effective theoretical model of both the static and dynamic properties of ferrimagnets was developed. It allows the description of all the observed experimental results. Using this formalism, we analytically and numerically studied the domain wall dynamics driven by field or spin-currents thus revealing new propagation regimes such as precession-free dynamics or the vanishing of transient motions.
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https://tel.archives-ouvertes.fr/tel-02903018
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Submitted on : Monday, July 20, 2020 - 3:34:14 PM
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  • HAL Id : tel-02903018, version 1

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Eloi Haltz. Domain wall dynamics driven by spin-current in ferrimagnetic alloys. Materials Science [cond-mat.mtrl-sci]. Université Paris Saclay (COmUE), 2019. English. ⟨NNT : 2019SACLS607⟩. ⟨tel-02903018⟩

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