Amélie Juhin > Research  

  Research Highlights

Research Interests

  • Electronic and magnetic properties of magnetic nanosized objects: 
          molecular magnets grafted on surfaces, core-shell nanoparticles, ferrofluids, photomagnetic systems
  • Experimental and theoretical  aspects of soft and hard x-ray spectroscopies
  • Development of RIXS-MCD with hard x-rays, a novel (photon-in, photon out)  magnetic spectroscopy


Experimental methods : core level spectroscopies on synchrotron radiation facilities (mainly ESRF and SOLEIL)
  • X-ray Absorption Spectroscopy (XANES, EXAFS) in situ and ex-situ
  • X-ray Emission Spectroscopy (XES)
  • Resonant Inelastic X-ray Scattering (RIXS)
  • Magnetic Spectroscopies: XMCD (X-ray Magnetic Circular Dichroism) and RIXS-MCD



Theoretical methods : modeling of core level spectroscopies and dichroisms (XAS, RIXS, XMCD, XNLD, XNCD)

  • Single particle calculations (DFT, DFT+U) : QUANTUM-ESPRESSO, FEFF, FDMNES
  • Multielectronic calculations (Ligand Field Multiplet Theory): Quanty, CTM4XAS, TT MULTIPLETS
  • Tensor analysis of spectroscopies



Principle of RIXS-MCD

        RIXS-MCD is a newly developed spectroscopy that combines photon-in, photon-out Resonant Inelastic X-ray Scattering (RIXS) with X-ray Magnetic Circular Dichroism (XMCD).

        When performed at the K pre-edge of 3d elements (1s2 2p6 3dN --> 1s1 2p6 3dN+1 --> 1s2 2p5 3dN+1), it exploits the advantages of hard x-rays (i.e., bulk sensitivity, low self-absorption effects)

        with the high resolution of RIXS.

       Recently, it was shown that hard x-ray RIXS-MCD can be a valuable alternative to soft x-ray XMCD, when using demanding sample environments, such as liquid and gas cells, or when investigating materials whose surface may not be representative of bulk properties.  

 

        Additionally, the 2D character (photon-in, photon-out) of RIXS-MCD enables to better disentangle the spectroscopic signatures of different valences.  

        The figure below illustrates the principle of a RIXS-MCD experiment (left), and the RIXS and RIXS-MCD planes measured at the Fe K edge in magnetite. 

                                                                                              

M. Sikora, A. Juhin, T.-S.Weng, Ph. Sainctavit, C. Detlefs, F. M. F. de Groot, and P. Glatzel. Strong K-edge XMCD effect in magnetite using photon in - photon out spectroscopy.

Physical Review Letters 105,037202 (2010) and ESRF Highlights 2010, 18-19. Spotlight on the ESRF website.



Applications of RIXS-MCD


  •         Multilayered systems

RIXS-MCD can be applied in a quantitative way to investigate systems for which the use of soft x-rays is rather challenging, such as 15 nm-thick magnetic layers buried under 60 nm Au / Pt, for which element- and site- selective hysteresis loops were measured.

M. Sikora, A. Juhin, G. Simon, M. Zaj.c, K. Biernacka, Cz. Kapusta, L. Morellon, M. R. Ibarra, and P. Glatzel, Journal of Applied Physics, 111, 07E301(2012).

 

  •         Bimagnetic core-shell nanoparticles 

Bi-magnetic core-shell nanoparticles currently focus high interest owing to their applications in the fields of biomedicine (hyperthermia, highly sensitive biosensors, improved MRI...) and technology (magnetic recording, permanent magnets…). The fine tailoring of particles requires a deep knowledge of their internal structure and morphology, from which the properties are directly inherited. In nominally γ-Fe2O3/Mn3O4 nanoparticles, RIXS-MCD is the smoking gun evidence for the existence of a magnetic interdiffused inner shell of (Mn,Fe) spinel growing from the core γ-Fe2O3 and the shell Mn3O4. Combined with TEM-EELS experiments, a quantitative multilayered “onion” structure is proposed (Figure below), which allows understanding the influence of the interface quality on the measured magnetic properties.


A. Juhin, A. López-Ortega, M. Sikora, C. Carvallo, M. Estrader, S. Estradé, F. Peiró, M. D. Baró, P. Sainctavit, P.Glatzel, and J. Nogués, Nanoscale, 6, 11911-11920 (2014).

  •         Ferrofluids
Recently, the magnetic anisotropies in a ferrofluid of monodispersed core@shell nanoparticles dispersed in heptane have been studied. Ferrofluids are well-known for their applications in optical waveguides, medicine (MRI, hyperthermia) or in fine arts (photo below). Their magnetic properties arise from both the magnetic anisotropies of individual particles and the interparticular interactions that are mediated by the liquid carrier. Using a specially-designed liquid cell (below), developed by Niéli Daffé (PhD student LabEx MATISSE) and ID26 beamline of the ESRF (M. Rovezzi) we have measured RIXS-MCD spectra and element selective hysteresis loops in the liquid phase and in the frozen phase. This has allowed investigating separately the cationic distribution and magnetic anisotropies in the core and those in the shell, as well as their mutual influence.
                                                

 N. Daffé, M. Sikora, N. Mas, V. Gavrilov, S. Neveu, F. Choueikani, V. Dupuis, M. Rovezzi, Ph. Ohresser, Ph. Sainctavit and A. Juhin, Advanced Materials Interfaces 22, 1700599 (2017) .  Crédits photos Niéli Daffé.