Reproducible formation of single magnetic bubbles in an array of patterned dots

International audienceThe formation conditions of single magnetic bubbles through in-plane field demagnetizationare investigated in an array of Co/Ni circular dots by magnetic force microscopy andcompared to micromagnetic calculations. We demonstrate high success rates in nucleatingstable bubbles. The efficiency of single bubble formation is found to depend not only on thedot size, material thickness and intrinsic material parameters but also on the bubble nucleationpath. Experimental phase diagrams and micromagnetic calculations highlight the influenceof the starting in-plane field amplitude and dipolar interactions in stabilizing the bubble.The identification of a systematic procedure for controlling nucleation of single bubbles,multidomain states or a uniform state is important from a technological point of view, openinga path toward the realization of reprogrammable magnonic crystals for the control of spinwavepropagation

High domain wall velocity at zero magnetic field induced by low current densities in spin-valve nanostripes

Current-induced magnetic domain wall motion at zero magnetic field is observed in the permalloy layer of a spin-valve-based nanostripe using photoemission electron microscopy. The domain wall movement is hampered by pinning sites, but in between them high domain wall velocities (exceeding 150 m/s) are obtained for current densities well below 10^{12} \unit{A/m^2}, suggesting that these trilayer systems are promising for applications in domain wall devices in case of well controlled pinning positions. Vertical spin currents in these structures provide a potential explanation for the increase in domain wall velocity at low current densities.Comment: Published version, Applied Physics Express 2, 023003 (2009) http://dx.doi.org/10.1143/APEX.2.02300

Unravelling the role of the interface for spin injection into organic semiconductors

Whereas spintronics brings the spin degree of freedom to electronic devices, molecular/organic electronics adds the opportunity to play with the chemical versatility. Here we show how, as a contender to commonly used inorganic materials, organic/molecular based spintronics devices can exhibit very large magnetoresistance and lead to tailored spin polarizations. We report on giant tunnel magnetoresistance of up to 300% in a (La,Sr)MnO3/Alq3/Co nanometer size magnetic tunnel junction. Moreover, we propose a spin dependent transport model giving a new understanding of spin injection into organic materials/molecules. Our findings bring a new insight on how one could tune spin injection by molecular engineering and paves the way to chemical tailoring of the properties of spintronics devices.Comment: Original version. Revised version to appear in Nature Physics

Graphene-passivated nickel as an oxidation-resistant electrode for spintronics.

We report on graphene-passivated ferromagnetic electrodes (GPFE) for spin devices. GPFE are shown to act as spin-polarized oxidation-resistant electrodes. The direct coating of nickel with few layer graphene through a readily scalable chemical vapor deposition (CVD) process allows the preservation of an unoxidized nickel surface upon air exposure. Fabrication and measurement of complete reference tunneling spin valve structures demonstrate that the GPFE is maintained as a spin polarizer and also that the presence of the graphene coating leads to a specific sign reversal of the magneto-resistance. Hence, this work highlights a novel oxidation-resistant spin source which further unlocks low cost wet chemistry processes for spintronics devices.R.S.W. acknowledges funding from EPSRC (Doctoral training award). S.H. acknowledges funding from ERC Grant InsituNANO (Project Reference 279342). P.S. acknowledges the Institut Universitaire de France for junior fellowship support. This research was partially supported by the EU FP7 work programme under Grant GRAFOL (Project Reference 285275).This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/nn304424x

Interdependency of subsurface carbon distribution and graphene-catalyst interaction.

The dynamics of the graphene-catalyst interaction during chemical vapor deposition are investigated using in situ, time- and depth-resolved X-ray photoelectron spectroscopy, and complementary grand canonical Monte Carlo simulations coupled to a tight-binding model. We thereby reveal the interdependency of the distribution of carbon close to the catalyst surface and the strength of the graphene-catalyst interaction. The strong interaction of epitaxial graphene with Ni(111) causes a depletion of dissolved carbon close to the catalyst surface, which prevents additional layer formation leading to a self-limiting graphene growth behavior for low exposure pressures (10(-6)-10(-3) mbar). A further hydrocarbon pressure increase (to ∼10(-1) mbar) leads to weakening of the graphene-Ni(111) interaction accompanied by additional graphene layer formation, mediated by an increased concentration of near-surface dissolved carbon. We show that growth of more weakly adhered, rotated graphene on Ni(111) is linked to an initially higher level of near-surface carbon compared to the case of epitaxial graphene growth. The key implications of these results for graphene growth control and their relevance to carbon nanotube growth are highlighted in the context of existing literature.R.S.W. acknowledges a Research Fellowship from St. John’s College, Cambridge. S.H. acknowledges funding from ERC grant InsituNANO (No. 279342) and EPSRC under grant GRAPHTED (Ref. EP/K016636/1). We acknowledge the Helmholtz-Zentrum-Berlin Electron storage ring BESSY II for provision of synchrotron radiation at the ISISS beamline and we thank the BESSY staff for continuous support of our experiments. This research was partially supported by the EU FP7 Work Programme under grant Graphene Flagship (No. 604391). PRK acknowledges funding the Cambridge Commonwealth Trust. H.A. and C.B. acknowledge J.-Y. Raty and B. Legrand for fruitful discussions.This is the final published version. It's also available from ACS at http://pubs.acs.org/doi/abs/10.1021/ja505454v

Dependência do exchange-bias e da coercividade da espessura do Cu em IrMn/Cu/Co

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