Blanc SIMI 4 - Blanc - SIMI 4 - Physique

Embedded magnetic nanowires – EMA

EMA: Embedded magnetic nanowires

Study of the growth and physical properties of self-assembled ferromagnetic nanowires with diameters in the 1-5 nm range.

Growth of ferromagnetic nanowires and integration within epitaxial heterostructures

-to grow ferromagnetic nanowires with a diameter between 1 and 5 nm and to study their electrical and magnetic properties. In this range of dimensions, the diameter of the nanowires is comparable or smaller than the physical characteristic lengths such as the critical diameter for coherent reversal, or the domain wall width. This makes nanowires very interesting objects for original studies in nanomagnetism. <br /> <br />-to validate strategies for the integration of nanowires in epitaxial heterostructures for subsequent use in nano-spintronics. This will include both growth and study of post-growth treatments, such as: determining the stability of nanowires under oxidizing treatment and modifying their aspect by annealing. <br />

The work program is divided into three tasks:

1 ) Growth and structure:

Controlled growth of nanowires : in order to determine the growth parameters controlling the diameter ( in the range 1-5 nm) and the density of the wires, systematic studies as a function of the temperature and relative concentration of species will be carried out employing techniques such as X-ray diffraction, X -ray absorption spectroscopy at SOLEIL, and electron microscopy.

2) Physical Properties:

Nanomagnetism : Magnetic measurements as a function of diameter will be made available on the SQUID magnetometer at INSP and VSM ( vibrating sample magnetometer ) magnetometer installed on the NovaTeCs platformin GEMaC ( PPMS , physical properties measurement system, C'nano IDF 2008 project). The results will be compared to existing models and magnetic simulations.

Electrical transport: global and local measurements (measurement on a single wire ) will be performed. This requires to initiate the growth on a conductive substrate, such as niobium-doped SrTiO3 that has the ad hoc characteristics for epitaxial growth of the proposed compounds and good electrical conductivity. Conductivity measurements will be performed on the regional platform NovaTeCs and by atomic force microscopy (AFM) with a conductive tip.

3) Post- growth treatments:
This perspective will be examined by monitoring oxidation by magneto-optical measurements and ellipsometry, magnetic measurements at high temperatures (400-1000 K), and X-ray absorption spectroscopy at the synchrotron under controlled conditions. These studies will benefit from feedback from observations by high resolution electron microscopy conducted in the framework of task 1.

1. Mechanism of Localization of the Magnetization Reversal in 3 nm Wide Co Nanowires
F. Vidal, Y. Zheng, P. Schio, F. J. Bonilla, M. Barturen, J. Milano, D. Demaille, E. Fonda, A. J. A. de Oliveira, V. H. Etgens
Physical Review Letters 109 (2012) 117205

Fundamental study on the link between structure and magnetic properties in 3 nm wide Co nanowires that shows the relation between axial variations of anisotropy and localized nucleation of the magnetization reversal.

2. Combinatorial Growth and Anisotropy Control of Self-Assembled Epitaxial Ultrathin Alloy Nanowires
F.J. Bonilla, A. Novikova, F. Vidal, Y. Zheng, E. Fonda, D. Demaille, V. Schuler, A. Coati, A. Vlad, Y. Garreau, M. Sauvage-Simkin, Y. Dumont, S. Hidki, V.H. Etgens
ACS Nano 7 (2013) 4022

Development of a new technique to grow epitaxial alloy nanowires in matrix. The growth technique is based on a combinatorial approach of pulsed laser deposition. By sequential deposition, in a submonolayer regime, of controlled amount of Co, Ni and ceria on a SrTiO3(001) substrate, it is possible to obtain 4 nm diameter slef-assembled nanowires made of CoNi alloy that grow epitaxially within the CeO2/SrTiO3(001) matrix.

Epitaxial integration of nanowires in functional devices for fundamental studies in nanomagnetism and spintronics.

1. Mechanism of Localization of the Magnetization Reversal in 3 nm Wide Co Nanowires
F. Vidal, Y. Zheng, P. Schio, F. J. Bonilla, M. Barturen, J. Milano, D. Demaille, E. Fonda, A. J. A. de Oliveira, V. H. Etgens
Physical Review Letters 109 (20

Ferromagnetic (FM) nanowires (NWs) and nanoparticles (NPs) have been the subject of intense research in recent years. Such objects could be used as fundamental units in magnetic storage devices. Because of their high aspect ratio (diameter of 10-100 nm, length potentially above 1 µm), NWs have large magnetic shape anisotropy. The consequence is that the magnetization prefers to lie along the axis of the wires. The existence of these two stable saturated states (magnetization pointing up or down) could be exploited in magnetic memory devices with high density. Alternating FM metals and paramagnetic ones along the NWs axis led to the successful design of nano-pillar exhibiting giant magneto-resistance (GMR), i.e. a substantial change of their resistance with varying magnetic field. Despite the attractive perspectives offered by FM NWs, there are still hurdles to overcome en route towards their use in functional devices, such as their successful integration in epitaxial heterostructures. Such an achievement would enable original nanospintronics studies to be carried out. Further lateral size reduction may be envisioned, enabled by a proper choice of the growth technique. With the most widely used methods, it is not possible to reduce diameters below 5-7 nm. The possibility to study the NWs magnetic properties in the 1-5 nm diameter range is an exciting issue. Most currently used techniques in order to elaborate NWs assemblies consist in filling the pores of a template with a ferromagnetic material. The template is made of polymers or porous alumina and filling the pores is most often done by electro-deposition. Such processes allow one to obtain fairly well-ordered assemblies, high wire length (higher than 1 micron), and hybrid wires made of alternating metals (e.g. Co/Cu for GMR). However, they also have some limits: the diameter of the wires is higher than ~5-7 nm, the density is rather high, epitaxial integration is difficult. We have demonstrated recently the possibility to obtain assemblies of ferromagnetic nanowires with much reduced diameters, down to 3 nm. These NWs form spontaneously during the growth of CeO2 epilayers containing cobalt, deposited by pulsed laser deposition (PLD) on SrTiO3(001). Given this context, the objectives pursued in this project are:
-Elaborate ferromagnetic nanowires with diameters between 1 and 5 nm and study their electrical and magnetic properties. In this range of dimensions, the diameter is of the same order of magnitude, or lower, than characteristic physical lengths such as the critical diameter for coherent rotation reversal or the domain wall width. This makes FM NWs very interesting objects for original studies in nanomagnetism.
-Validate strategies in order to integrate nanowires in epitaxial heterostructures en route towards their subsequent use in nano-spintronics. This will imply both growth studies and post-growth treatments, such as, for example: determining the stability of NWs under oxidant conditions and modifying their aspect through thermal treatments (transformation of a wire into a chain of aligned clusters through triggering of the Rayleigh instability?).

Project coordinator

Monsieur Franck VIDAL (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR PARIS B) – franck.vidal@insp.jussieu.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

GEMAC CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR OUEST ET NORD
SOLEIL SYNCHROTRON SOLEIL
INSP CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR PARIS B

Help of the ANR 681,787 euros
Beginning and duration of the scientific project: December 2011 - 36 Months

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