Thermal simulation of magnetization reversals for size-distributed assemblies of core-shell exchange biased nanoparticles

A temperature dependent coherent magnetization reversal model is proposed for size-distributed assemblies of ferromagnetic nanoparticles and ferromagnetic-antiferromagnetic core-shell nanoparticles. The nanoparticles are assumed to be of uniaxial anisotropy and all aligned along their easy axis. The thermal dependence is included by considering thermal fluctuations, implemented via the N\'eel-Arrhenius theory. Thermal and angular dependence of magnetization reversal loops, coercive field and exchange-bias field are obtained, showing that F-AF size-distributed exchange-coupled nanoparticles exhibit temperature-dependent asymmetric magnetization reversal. Also, non-monotonic evolutions of He and Hc with T are demonstrated. The angular dependence of Hc with T exhibits a complex behavior, with the presence of an apex, whose position and amplitude are strongly T dependent. The angular dependence of He with T exhibits complex behaviors, which depends on the AF anisotropy and exchange coupling. The resulting angular behavior demonstrates the key role of the size distribution and temperature in the magnetic response of nanoparticles.Comment: Revised arguments in Introduction and last sectio

FMR studies of exchange-coupled multiferroic polycrystalline Pt/BiFeO3_3/Ni81_{81}Fe19_{19}/Pt heterostructures

An experimental study of the in-plane azimuthal behaviour and frequency dependence of the ferromagnetic resonance field and the resonance linewidth as a function of BiFeO$_3$ thickness is carried out in a polycrystalline exchange-biased BiFeO$_3$/Ni$_{81}$Fe$_{19}$ system. The magnetization decrease of the Pt/BiFeO$_3$/Ni$_{81}$Fe$_{19}$/Pt heterostructures with BiFeO$_3$ thickness deduced from static measurements has been confirmed by dynamic investigations. Ferromagnetic resonance measurements have shown lower gyromagnetic ratio in a perpendicular geometry compared with that of a parallel geometry. The monotonous decrease of gyromagnetic ratio in a perpendicular geometry as a function of the BiFeO$_3$ film thickness seems to be related to the spin-orbit interactions due to the neighbouring Pt film at its interface with Ni$_{81}$Fe$_{19}$ film. The in-plane azimuthal shape of the total linewidth of the uniform mode shows isotropic behaviour that increases with BiFeO$_3$ thickness. The study of the frequency dependence of the resonance linewidth in a broad band of 3 to 35 GHz has allowed the determination of intrinsic and extrinsic contributions to the relaxation as function of BiFeO$_3$ thickness in perpendicular geometries. In our system the magnetic relaxation is dominated by the spin-pumping mechanism due to the presence of Pt. The insertion of BiFeO$_3$ between Pt and Ni$_{81}$Fe$_{19}$ attenuates the spin-pumping damping at one interface.Comment: paper accepted for publication in the Journal of Physics D: Applied Physic

Experimental method to determine the misalignment of the easy axis of ferromagnetic and antiferromagnetic films in exchange biased bilayers

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Study of dynamic properties and magnetic anisotropies of NiFe/MnPt in the critical thickness range

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Experimental method to determine the misalignment of the easy axis of ferromagnetic and antiferromagnetic films in exchange biased bilayers

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Experimental evidence for the role of nonuniform modes in the asymmetric magnetization reversal of a Ni ∕ NiO system

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Asymmetric magnetization reversal behavior in exchange-biased NiFe∕MnPt bilayers in two different anisotropy regimes: Close and far from critical thickness

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Surfactant-mediated growth of Cu on Co(0001) investigated using medium-energy ion scattering

Experiments were carried out using medium energy ion scattering (MEIS) to compare the structural properties of Cu films deposited on Co(0001) both with and without surfactant and before and after annealing to 300 °C. Films of 10-ML thickness were deposited onto the clean Co surface and onto a surface pre-dosed with 1 ML of Pb surfactant. MEIS data revealed a twinned fcc structure in all the deposited films irrespective of the presence of surfactant or the use of post deposition annealing. In the case of the Pb deposited surfaces the majority of surfactant was seen to float on the surface during growth but with a small quantity becoming distributed throughout the film. In addition to allowing 1-2 extra monolayers to grow epitaxially, the MEIS data provided evidence of improved crystallinity for films grown with the surfactant. Annealing the sample to 300 °C appeared to have little or no effect on the deposited films

Experimental evidence for the role of nonuniform modes in the asymmetric magnetization reversal of a Ni ∕ NiO system

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Probing misalignment in exchange biased systems: A dynamic approach

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