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Register a new userAttempt frequency of magnetization in nanomagnets with thin-film geometry
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Solving the stochastic Landau-Lifshitz-Gilbert equation numerically, we investigate the effect of the potential landscape on the attempt frequency of magnetization in nanomagnets with the thin-film geometry. Numerical estimates of the attempt frequency are analyzed in comparison with theoretical predictions from the Fokker-Planck equation for the Neel-Brown model. It is found that for a nanomagnet with the thin-film geometry, theoretically predicted values for the universal case are in excellent agreement with numerical estimates.
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The interface between organic semiconductor [OSC]/ferromagnetic [FM] material can exhibit ferromagnetism due to their orbital hybridization. Charge/spin transfer may occur from FM to OSC layer leading to the formation of `spinterface i.e. the interface exhibiting a finite magnetic moment. In this work, the magnetic properties of Co/C$_{60}$ bilayer thin film have been studied to probe the interface between Co and C$_{60}$ layer. Polarized neutron reflectivity [PNR] measurement indicates that the thickness and moment of the spinterface are $sim$ 2 $pm$ 0.18 nm and 0.8 $pm$ 0.2 $mu_B$/cage, respectively. The comparison of the magnetization reversal between the Co/C$_{60}$ bilayer and the parent single layer Co thin film reveals that spinterface modifies the domain microstructure. Further, the anisotropy of the bilayer system shows a significant enhancement ($sim$ two times) in comparison to its single layer counterpart which is probably due to an additional interfacial anisotropy arising from the orbital hybridization at the Co/C$_{60}$ interface.
Nanowires with very different size, shape, morphology and crystal symmetry can give rise to a wide ensemble of magnetic behaviors whose optimization determines their applications in nanomagnets. We present here an experimental work on the shape and morphological dependence of the magnetization reversal mechanism in weakly interacting Co80Ni20 hexagonal-close-packed nanowires. Non-agglomerated nanowires (with length L and diameter d) with a controlled shape going from quasi perfect cylinders to diabolos, have been studied inside their polyol solution in order to avoid any oxidation process. The coercive field HC was found to follow a standard behavior and to be optimized for an aspect ratio L/d > 15. Interestingly, an unexpected behavior was observed as function of the head morphology leading to the strange situation where a diabolo shaped nanowire is a better nanomagnet than a cylinder. This paradoxical behavior can be ascribed to the growth-competition between the aspect ratio L/d and the head morphology ratio d/D (D being the head width). Our experimental results clearly show the importance of the independent parameter (t = head thickness) that needs to be considered in addition to the shape aspect ratio (L/d) in order to fully describe the nanomagnets magnetic behavior. Micromagnetic simulations well support the experimental results and bring important insights for future optimization of the nanomagnets morphology
Microstripline ferromagnetic resonance technique has been used to study the indirect magnetoelectric coupling occurring in an artificial magnetoelectric heterostructure consisting of a magnetostrictive thin film cemented onto a piezoelectric actuator. Two different modes (sweep-field and sweep-frequency modes) of this technique have been employed to quantitatively probe the indirect magnetoelectric coupling and to observe a voltage induced magnetization rotation (of 90 degree). This latter has been validated by the experimental frequency variation of the uniform mode and by the amplitude of the sweep-frequency spectra.
Low-dimensional boundaries between phases and domains in organic thin films are important in charge transport and recombination. Here, fluctuations of interfacial boundaries in an organic thin film, acridine-9-carboxylic acid (ACA) on Ag(111), have been visualized in real time, and measured quantitatively, using Scanning Tunneling Microscopy. The boundaries fluctuate via molecular exchange with exchange time constants of 10-30 ms at room temperature, yielding length mode fluctuations that should yield characteristic f-1/2 signatures for frequencies less than ~100 Hz. Although ACA has highly anisotropic intermolecular interactions, it forms islands that are compact in shape with crystallographically distinct boundaries that have essentially identical thermodynamic and kinetic properties . The physical basis of the modified symmetry is shown to arise from significantly different substrate interactions induced by alternating orientations of successive molecules in the condensed phase. Incorporating this additional set of interactions in a lattice gas model leads to effective multi-component behavior, as in the Blume-Emery-Griffiths (BEG) model, and can straightforwardly reproduce the experimentally observed isotropic behavior. The general multi-component description allows the domain shapes and boundary fluctuations to be tuned from isotropic to highly anisotropic in terms of the balance between intermolecular interactions and molecule-substrate interactions. Key words: Organic thin film, fluctuations, STM, molecular interactions, diffusion kinetics, phase coexistence
Rare earth nickelates RENiO3 which attract interest due to their sharp metal-insulator phase transition, are instable in bulk form due to the necessity of an important oxygen pressure to stabilize Ni in its 3+ state of oxidation. Here, we report the stabilization of rare earth nickelates in [(SmNiO3)t/(NdNiO3)t]n thin film multilayers, t being the thickness of layers alternated n times. Both bilayers and multilayers have been deposited by Metal-Organic Chemical Vapour Deposition. The multilayer structure and the presence of the metastable phases SmNiO3 and NdNiO3 are evidenced from by X-ray and Raman scattering. Electric measurements of a bilayer structure further support the structural quality of the embedded rare earth nickelate layers.
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