Spin dynamics and structural modifications of Co2MnSi Heusler alloys by Helium ions irradiation

Abstract : Spintronic, which involve electron's in addition to its charge, has emerged from the discovery of Giant Magnetoresistance (GMR) by A. Fert and P. Grunberg in 1988, rewarded by a Nobel Prize in 2007. It has revolutionized the field of sensor devices. The basic mechanism of GMR and also of the Tunneling Magneto Resistance (TMR) relies on the spin polarization. Therefore there is today an intense research to find materials with both high spin polarization and low damping coefficient for the development of new generation of spintronic devices. In this field, one promising route concerns the Co2MnSi (CMS) Heusler alloy which is predicted to be half metals (i.e.100% spin polarization), with a weak Gilbert damping coefficient below 10^-3, about one order of magnitude below the usual ferromagnetic material used in microelectronics. Its high Curie temperature up to 800° K also provides stability for devices working at room temperature. In this work, we study the correlations between the structural and magnetic properties of the Co2MnSi. To achieve our goal, we measure the evolution of the static and dynamic magnetic parameters of the Co2MnSi alloy in which atomic disorder is induced by He+ ion irradiation at 150 KeV. The samples are grown by magnetron sputtering on MgO substrates and then irradiated with light He+ ions. In order to correlate the structural and magnetic modifications of the alloy we combined several experimental techniques. CMS structure was investigated by X-ray diffraction and Transmission Electron Microscopy (TEM), in particular HAADF-STEM imaging mode. The evolution of the static and dynamic magnetic properties of the samples has been measured by means of Magneto Optic Kerr Effect (MOKE), Physical Properties Measurements System (PPMS) at the LPCNO laboratory in Toulouse and Ferromagnetic Resonance (FMR). The FMR set-up has been developed at the CEMES during this PhD. The main results of this work consists of correlation between the tetragonal deformations of the crystalline structure followed by the appearance of uniaxial anisotropy in the material upon irradiation. Furthermore, we demonstrate that the magnetic parameters of the B2 order are slightly affected by irradiation. But for the L21 phase, static and dynamic magnetic properties are drastically affected by irradiation, by the decrease in magnetization saturation, and exchange constant due to the Mn/Co disorder type and an increase of the cubic anisotropy and dynamic relaxation.
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Contributor : Iman Abdallah <>
Submitted on : Friday, December 16, 2016 - 12:15:55 PM
Last modification on : Monday, April 29, 2019 - 3:59:02 PM
Long-term archiving on : Monday, March 20, 2017 - 8:12:20 PM

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  • HAL Id : tel-01405819, version 2

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Iman Abdallah. Spin dynamics and structural modifications of Co2MnSi Heusler alloys by Helium ions irradiation . Materials Science [cond-mat.mtrl-sci]. Université Paul Sabatier - Toulouse III, 2016. English. ⟨NNT : 2016TOU30079⟩. ⟨tel-01405819v2⟩

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