Self-organization of FePt nanoparticles on a moiré pattern probed by Grazing Incidence Small-Angle X-Ray Scattering

QUICK INFORMATION
Type
Seminar
Start Date
08-11-2017 14:00
Location
Room 337, Central Building
Speaker's name
Dr Pierre Capiod
Speaker's institute
Université de Lyon
Contact name
Ewa Wyszynska
Host name
Gilles Renaud
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Self-organization of FePt nanoparticles on a moiré pattern probed by Grazing Incidence Small-Angle X-Ray Scattering

1. Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS,

Université de Lyon, 69622 Villeurbanne cedex, France

2.Commissariat à l’Energie Atomique, Institut Nanosciences et Cryogénie,

Service de Physique des Matériaux et Microstructures, Nanostructures et Rayonnement Synchrotron,

17 Avenue des Martyrs, F-38054 Grenoble, Cedex 9, France

 

The FePt bulk alloy, when chemically ordered in the L10 phase, is among the magnetic materials displaying the highest magnetic anisotropy constant (K around 7 MJ/m3). Therefore it is a perfect candidate for ultra-high density magnetic storage applications, provided nanoparticles can be prepared in such a high anisotropy phase : The chemically ordered L10 phase[1]. Another requirement for applications, as well as for fundamental studies, is to organize the magnetic nanoparticles in a 2D array. In parallel to investigations on chemically synthesized systems, a great effort is devoted to the bottom-up elaboration of nanomagnet arrays following a physical route.

In this context, one widely used path consists in using template surfaces with specific sites regularly distributed. Such a 2D lattice can be obtained with the moiré phenomenon, which appears when two crystalline structures of slightly different cell parameters are stacked. Thus, a graphene layer epitaxially grown by CVD on a Ir(111) surface displays a 2D spatial modulation corresponding to a hexagonal lattice of 2.5 nm cell parameter[2]. For the first time, we have characterized the auto-organization of FePt nanoparticles on such a moiré pattern by Grazing Incidence Small-Angle X-Ray Scattering (GISAXS).

 

 

 

 

 

FIG. 1: (a) GISAXS pattern along the <100> direction of the moiré before (left) and after (right) annealing, of 2.2 nm diameter FePt nanoparticles on graphene/Ir(111) substrate. The correlation peak (highligthed in red) points out the organization of the nanoparticles on the surface. (b) Normalized intensity of the correlation peak taken at α = 8 mrad along the 2θ direction for the 2.2 nm nanoparticles sample. Data and fit are respectively in colored curves and black curves.

I will first describe the synthesis of the FePt nanoparticles and the annealing at high temperature in UHV to obtain the L10 phase transition . The auto-organization characterized by GISAXS corresponds to the presence of a correlation peak (highlighted in red on the fig. 1(a)). This correlation peak is a constructive interference coming from the organization of the nanoparticles on the surface. Hence, the more nanoparticles are organized, the more intense the peak will be. The auto-organization can be quantified from the correlation peak. I will link the intensity of the peak to the percentage Θ of nanoparticles pinned on the moiré surface (fig.  1(b)).  We have investigated several samples of FePt nanoparticles on a moiré pattern with by varying various parameters : nanoparticles size, deposition temperature, capping layer, annealing temperature. I will show the influence of those parameters on the intensity of the correlation peak and on the organization of the particles. Those results will be confronted to a simulation model in view to establish the dynamic and the evolution of the particles on the surface.

[1] P. Andreazza, V. Pierron-Bohnes, F. Tournus, C. Andreazza-Vignolle, and V. Dupuis, Surface Science Reports 70, 188 (2015). [2] A. T. N’Diaye, J. Coraux, T. N. Plasa, C. Busse, and T. Michely, New Journal of Physics 10, 043033 (2008).

[2] A. T. N’Diaye, J. Coraux, T. N. Plasa, C. Busse, and T. Michely, New Journal of Physics 10, 043033 (2008).

 

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