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      Dynamical Torque in Co x Fe 3– x O 4 Nanocube Thin Films Characterized by Femtosecond Magneto-Optics: A π-Shift Control of the Magnetization Precession

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          For spintronic devices excited by a sudden magnetic or optical perturbation, the torque acting on the magnetization plays a key role in its precession and damping. However, the torque itself can be a dynamical quantity via the time-dependent anisotropies of the system. A challenging problem for applications is then to disentangle the relative importance of various sources of anisotropies in the dynamical torque, such as the dipolar field, the crystal structure or the shape of the particular interacting magnetic nanostructures. Here, we take advantage of a range of colloidal cobalt ferrite nanocubes assembled in 2D thin films under controlled magnetic fields to demonstrate that the phase, ϕ Prec, of the precession carries a strong signature of the dynamical anisotropies. Performing femtosecond magneto-optics, we show that ϕ Prec displays a π-shift for a particular angle θ H of an external static magnetic field, H. θ H is controlled with the cobalt concentration, the laser intensity, as well as the interparticle interactions. Importantly, it is shown that the shape anisotropy, which strongly departs from those of equivalent bulk thin films or individual noninteracting nanoparticles, reveals the essential role played by the interparticle collective effects. This work shows the reliability of a noninvasive optical approach to characterize the dynamical torque in high density magnetic recording media made of organized and interacting nanoparticles.

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          Most cited references 47

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          Ultrafast spin dynamics in ferromagnetic nickel.

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            Simple analytical expression for the peak-frequency shifts of plasmonic resonances for sensing

            We derive a closed-form expression that accurately predicts the peak frequency-shift and broadening induced by tiny perturbations of plasmonic nanoresonators without critically relying on repeated electrodynamic simulations of the spectral response of nanoresonator for various locations, sizes or shapes of the perturbing objects. The force of the present approach, in comparison with other approaches of the same kind, is that the derivation is supported by a mathematical formalism based on a rigorous normalization of the resonance modes of nanoresonators consisting of lossy and dispersive materials. Accordingly, accurate predictions are obtained for a large range of nanoparticle shapes and sizes, used in various plasmonic nanosensors, even beyond the quasistatic limit. The expression gives quantitative insight, and combined with an open-source code, provides accurate and fast predictions that are ideally suited for preliminary designs or for interpretation of experimental data. It is also valid for photonic resonators with large mode volumes.
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              Current-induced magnetization reversal in nanopillars with perpendicular anisotropy


                Author and article information

                Nano Lett
                Nano Lett
                Nano Letters
                American Chemical Society
                11 July 2016
                10 August 2016
                : 16
                : 8
                : 5291-5297
                []Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, CNRS, Université de Strasbourg , BP 43, 23 rue du Loess, 67034 Strasbourg Cedex 02, France
                []SUPA, School of Physics and Astronomy, University of St. Andrews , St Andrews KY16 9SS, United Kingdom
                [§ ]SUPA, Department of Physics and Astronomy, University of Glasgow , Glasgow G12 8QQ, United Kingdom
                []Elements Chemistry Laboratory, RIKEN , Wako 351-0198, Japan
                []Department of Physics, CNRS-Ewha International Research Center, Ewha W. University , Seoul 120-750, Republic of Korea
                Author notes
                Copyright © 2016 American Chemical Society

                This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.

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