The Experts below are selected from a list of 84 Experts worldwide ranked by ideXlab platform
F. Mazaleyrat - One of the best experts on this subject based on the ideXlab platform.
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Analytical modeling of demagnetizing effect in magnetoelectric ferrite/PZT/ferrite trilayers taking into account a mechanical coupling
Journal of Magnetism and Magnetic Materials, 2017Co-Authors: V. Loyau, Alex Aubert, M. Lobue, F. MazaleyratAbstract:In this paper, we investigate the demagnetizing effect in ferrite/PZT/ferrite magnetoelectric (ME) trilayer composites consisting of commercial PZT Discs bonded by epoxy layers to Ni-Co-Zn ferrite Discs made by a reactive Spark Plasma Sintering (SPS) technique. ME voltage coefficients (transversal mode) were measured on ferrite/PZT/ferrite trilayer ME samples with different thicknesses or phase volume ratio in order to highlight the influence of the Magnetic field penetration governed by these geometrical parameters. Experimental ME coefficients and voltages were compared to analytical calculations using a quasi-static model. Theoretical demagnetizing factors of two Magnetic Discs that interact together in parallel Magnetic structures were derived from an analytical calculation based on a superposition method. These factors were introduced in ME voltage calculations which take account of the demagnetizing effect. To fit the experimental results, a mechanical coupling factor was also introduced in the theoretical formula. This reflects the differential strain that exists in the ferrite and PZT layers due to shear effects near the edge of the ME samples and within the bonding epoxy layers. From this study, an optimization in magnitude of the ME voltage is obtained. Lastly, an analytical calculation of demagnetizing effect was conducted for layered ME composites containing higher numbers of alternated layers (). The advantage of such a structure is then discussed.
Peter J Metaxas - One of the best experts on this subject based on the ideXlab platform.
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frequency based nanoparticle sensing over large field ranges using the ferroMagnetic resonances of a Magnetic nanodisc
Nanotechnology, 2016Co-Authors: Maximilian Albert, Marijan Beg, Dmitri Chernyshenko, Marcantonio Bisotti, Rebecca Carey, Hans Fangohr, Peter J MetaxasAbstract:Using finite element microMagnetic simulations, we study how resonant magnetisation dynamics in thin Magnetic Discs with perpendicular anisotropy are influenced by magnetostatic coupling to a Magnetic nanoparticle. We identify resonant modes within the disc using direct Magnetic eigenmode calculations and study how their frequencies and spatial profiles are changed by the nanoparticle's stray Magnetic field. We demonstrate that particles can generate shifts in the resonant frequency of the disc's fundamental mode which exceed resonance linewidths in recently studied spin torque oscillator devices. Importantly, it is shown that the simulated shifts can be maintained over large field ranges (here up to 1 T). This is because the resonant dynamics (the basis of nanoparticle detection here) respond directly to the nanoparticle stray field, i.e. detection does not rely on nanoparticle-induced changes to the Magnetic ground state of the disc. A consequence of this is that in the case of small disc-particle separations, sensitivities to the particle are highly mode- and particle-position-dependent, with frequency shifts being maximised when the intense stray field localised directly beneath the particle can act on a large proportion of the disc's spins that are undergoing high amplitude precession.
V. Loyau - One of the best experts on this subject based on the ideXlab platform.
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Analytical modeling of demagnetizing effect in magnetoelectric ferrite/PZT/ferrite trilayers taking into account a mechanical coupling
Journal of Magnetism and Magnetic Materials, 2017Co-Authors: V. Loyau, Alex Aubert, M. Lobue, F. MazaleyratAbstract:In this paper, we investigate the demagnetizing effect in ferrite/PZT/ferrite magnetoelectric (ME) trilayer composites consisting of commercial PZT Discs bonded by epoxy layers to Ni-Co-Zn ferrite Discs made by a reactive Spark Plasma Sintering (SPS) technique. ME voltage coefficients (transversal mode) were measured on ferrite/PZT/ferrite trilayer ME samples with different thicknesses or phase volume ratio in order to highlight the influence of the Magnetic field penetration governed by these geometrical parameters. Experimental ME coefficients and voltages were compared to analytical calculations using a quasi-static model. Theoretical demagnetizing factors of two Magnetic Discs that interact together in parallel Magnetic structures were derived from an analytical calculation based on a superposition method. These factors were introduced in ME voltage calculations which take account of the demagnetizing effect. To fit the experimental results, a mechanical coupling factor was also introduced in the theoretical formula. This reflects the differential strain that exists in the ferrite and PZT layers due to shear effects near the edge of the ME samples and within the bonding epoxy layers. From this study, an optimization in magnitude of the ME voltage is obtained. Lastly, an analytical calculation of demagnetizing effect was conducted for layered ME composites containing higher numbers of alternated layers (). The advantage of such a structure is then discussed.
Olle Heinonen - One of the best experts on this subject based on the ideXlab platform.
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Direct Observation of Unconventional Topological Spin Structure in Coupled Magnetic Discs
Physical review letters, 2012Co-Authors: Charudatta Phatak, Amanda K. Petford-long, Olle HeinonenAbstract:Confined Magnetic thin films are known to exhibit a variety of fascinating topological spin states such as Skyrmions, vortices, and antivortices. Such topological excitations are fundamentally important to our understanding of quantum critical phenomenon and related phase transitions. Here we report on the direct observation of an unconventional topological spin state and its behavior in antiferroMagnetically coupled NiFe Discs at room temperature. The observed spin structure is similar to the theoretically predicted merons which have not yet been observed directly. We have used in situ Lorentz microscopy magnetizing experiments combined with microMagnetic simulations to follow the stability and the behavior of the meron state. The work presented in this paper will open new opportunities for direct experimental investigation of various topological states that can provide insights into the fundamental physics of their interactions.
Thomas Prokscha - One of the best experts on this subject based on the ideXlab platform.
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Collective magnetism in an artificial 2D XY spin system
Nature Communications, 2018Co-Authors: Naëmi Leo, Stefan Holenstein, Dominik Schildknecht, Oles Sendetskyi, Hubertus Luetkens, Peter M. Derlet, Valerio Scagnoli, Diane Lançon, José R. L. Mardegan, Thomas ProkschaAbstract:Two-dimensional Magnetic systems with continuous spin degrees of freedom exhibit a rich spectrum of thermal behaviour due to the strong competition between fluctuations and correlations. When such systems incorporate coupling via the anisotropic dipolar interaction, a discrete symmetry emerges, which can be spontaneously broken leading to a low-temperature ordered phase. However, the experimental realisation of such two-dimensional spin systems in crystalline materials is difficult since the dipolar coupling is usually much weaker than the exchange interaction. Here we realise two-dimensional magnetostatically coupled XY spin systems with nanoscale thermally active Magnetic Discs placed on square lattices. Using low-energy muon-spin relaxation and soft X-ray scattering, we observe correlated dynamics at the critical temperature and the emergence of static long-range order at low temperatures, which is compatible with theoretical predictions for dipolar-coupled XY spin systems. Furthermore, by modifying the sample design, we demonstrate the possibility to tune the collective Magnetic behaviour in thermally active artificial spin systems with continuous degrees of freedom. Magnetic metamaterials can be designed to provide models of frustrated systems that allow theoretical predictions to be experimentally tested. Here the authors realise a 2D XY model with dipolar interactions and find behaviour consistent with predictions of a low-temperature ordered state.
