Structural and magnetic properties of electrodeposited Fe x Ni 1-x ultra thin layers on Au(111)

Abstract : The magnetization of a film as well as its perpendicular magnetic anisotropy (PMA) are very sensitive to the film interfaces, to its morphology and to the atomic arrangement in the case of an alloy. The aim of this work is to investigate the magnetic properties of FexNi(1-x) ultrathin layers electrodeposited on Au(111) as a function their chemical composition and their atomic arrangement and to correlate them with their structural characterizations. For this purpose, we used real time in situ MOKE (Magneto-optical Kerr Effect), ex−situ extended X ray absorption fine structure (EXAFS) and ex−situ X−ray diffraction (XRD). Films of various composition were obtained by electrochemical co-reduction of the metal cations on the gold surface (Fe2+ and/or Ni2+), at a rate ~ 0.1 atomic mono-layer per second (ML/s). The film stoechiometry was determined as a function of the deposition potential and the film thickness. Appropriate conditions were found to obtain an alloy film with a single phase solid solution, and which stoechiometry is fixed by the solution composition. EXAFS and XRD show that the films are in epitaxy with the Au(111) substrate. However, they also demonstrate that the film structure is stoechiometry dependent, with a strained bcc (110) phase for iron rich films (e.g. Fe80Ni20) and a relaxed fcc phase for lower iron content (e.g. Fe50Ni50). For layered Fe films deposited on Ni, we found evidence for a relaxed bcc phase for Fe and relaxed fcc phase for Ni. STM observations show that the alloy and the layered films are atomically flat. MOKE evidences a thickness dependent magnetic reorientation transition out of plane magnetization to in plane magnetization for 0.5 < x <1 (iron rich alloys). Moreover, the average magnetic moment per atom varies linearly with x, but remains smaller than that expected for completely magnetized iron atoms. On the other hand, for a layered film, the average magnetic moment per atom is very close to that expected for completely magnetized iron and nickel atoms. The contribution of the structural differences and of the local environment of the Fe atoms is discussed to evaluate the origin of the different magnetic behaviors.
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Hugo Feitosa Jurca. Structural and magnetic properties of electrodeposited Fe x Ni 1-x ultra thin layers on Au(111). Condensed Matter [cond-mat]. Ecole polytechnique X, 2009. English. ⟨tel-01252766⟩

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