1,720,995 research outputs found
Controlling the three dimensional propagation of spin waves in continuous ferromagnetic films with an increasing out of plane undulation
No full textThe role of three-dimensionality in a ferromagnetic medium in ruling the propagation properties of spin-waves (SW) has been one of the main focuses of the research activity in recent years. In this context, we investigate the evolution of the SW dispersion (frequency vs wave vector) induced by a progressive vertical undulation of a ferromagnetic film. The geometric undulation is taken along a single direction and is periodic with constant period, while the amplitude (differential maximum height with respect to the film thickness) is gradually increased from 0 to 60 nm. We study the characteristic modification of the internal effective field and link it to the resulting SW dispersions and spatial profile. These systems display at once features both of a planar film and a discretized medium, and the dispersion curves change not only when SWs propagate along the undulation direction, but also perpendicular to it. We discuss the geometric and magnetic conditions for having either the invariance of the SW group velocity with respect to even major changes in the undulation, or a large group velocity for some edge modes. We address a potential dual-band activity, namely the simultaneous propagation of two independent SW-signals, with separated frequency bands and disjoint oscillation regions
A sinusoidal magnetization distribution as an original way to generate a versatile magnonic crystal for magnon propagation
Full text linkThe manipulation of the magnetization in a film at the nanoscale is one of the best means for controlling spin-wave propagation in real time. In 3D Magnonics, the vertical or interfacial interaction with patterned layers can make the film magnetization depart from uniformity, which, in general, can introduce new spin-wave modes in the film, hence additional degrees of freedom for signal manipulation. In this paper, we suggest a sinusoidal distribution for the magnetization as an original and effective way to generate a magnonic crystal and control its magnon dynamics. Along with a uniform bias field, we introduce in the film layer a sinusoidal bias field, simulating the vertical/interfacial interaction with other layers: after relaxation, the film magnetization assumes a sinusoidal equilibrium distribution. Using micromagnetic simulations followed by Fourier analysis, we show how to control the magnon dynamics by tuning the magnetization undulation amplitude and symmetry. We compute the magnon dispersion curves and space profiles, we show the occurrence of new degrees of freedom for signal manipulation and the rise of localized and stationary magnon modes. We highlight the physical mechanisms governing the occurrence and variation of the frequency-gap at zone-boundary. Finally, we indicate how to practically implement a sinusoidal field (and consequent magnetization) when the vertical coupling is the inverse magnetoelastic interaction between ferroelectric and ferromagnetic films. Our results suggest a new mechanism for controlling magnon propagation, which appears extremely appealing for its really wide range of tunable effects on their dynamics, particularly interesting in
the engineering of signal filtering, information storage and delivery, and sensing activity
A sinusoidal magnetization distribution as an original way to generate a versatile magnonic crystal for magnon propagation
No full textThe manipulation of the magnetization in a film at the nanoscale is one of the best means for controlling spin-wave propagation in real time. In 3D Magnonics, the vertical or interfacial interaction with patterned layers can make the film magnetization depart from uniformity, which, in general, can introduce new spin-wave modes in the film, hence additional degrees of freedom for signal manipulation. In this paper, we suggest a sinusoidal distribution for the magnetization as an original and effective way to generate a magnonic crystal and control its magnon dynamics. Along with a uniform bias field, we introduce in the film layer a sinusoidal bias field, simulating the vertical/interfacial interaction with other layers: after relaxation, the film magnetization assumes a sinusoidal equilibrium distribution. Using micromagnetic simulations followed by Fourier analysis, we show how to control the magnon dynamics by tuning the magnetization undulation amplitude and symmetry. We compute the magnon dispersion curves and space profiles, we show the occurrence of new degrees of freedom for signal manipulation and the rise of localized and stationary magnon modes. We highlight the physical mechanisms governing the occurrence and variation of the frequency-gap at zone-boundary. Finally, we indicate how to practically implement a sinusoidal field (and consequent magnetization) when the vertical coupling is the inverse magnetoelastic interaction between ferroelectric and ferromagnetic films. Our results suggest a new mechanism for controlling magnon propagation, which appears extremely appealing for its really wide range of tunable effects on their dynamics, particularly interesting in the engineering of signal filtering, information storage and delivery, and sensing activity
Collective spin waves in arrays of permalloy nanowires with single-side periodically modulated width
No full textWe have experimentally and numerically investigated the dispersion of collective spin waves propagating through arrays of longitudinally magnetized nanowires (NWs) with a periodically modulated width. Two nanowire arrays with single-side modulation and different periodicities of modulation were studied and compared to the nanowires with a homogeneous width. The spin-wave dispersion, measured up to the third Brillouin zone of the reciprocal space, revealed the presence of two dispersive modes for the width-modulated NWs, whose amplitude of the magnonic band depends on the modulation periodicity, and a set of nondispersive modes at higher frequency. These findings are different from those observed in homogeneous width NWs where only the lowest mode exhibits sizeable dispersion. The measured spin-wave dispersion has been satisfactorily reproduced by means of the dynamical matrix method. The results presented in this work are important in view of the possible realization of tunable frequency magnonic devices
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A Brillouin light scattering study of the spin-wave magnetic field dependence in a magnetic hybrid system made of an artificial spin-ice structure and a film underlayer
No full textWe present a combined Brillouin light scattering (BLS) and micromagnetic simulation investigation of the magnetic-field-dependent spin-wave spectra in a hybrid structure made of permalloy (NiFe) artificial spin-ice (ASI) systems, composed of stadium-shaped nanoislands, deposited on the top of an unpatterned permalloy film with a nonmagnetic spacer layer. The thermal spin-wave spectra were recorded by BLS as a function of the magnetic field applied along the symmetry direction of the ASI sample. Magneto-optic Kerr effect magnetometry was used to measure the hysteresis loops in the same orientation as the BLS measurements. The frequency and the intensity of several spin-wave modes detected by BLS were measured as a function of the applied magnetic field. Micromagnetic simulations enabled us to identify the modes in terms of their frequency and spatial symmetry and to extract information about the existence and strength of the dynamic coupling, relevant only to a few modes of a given hybrid system. Using this approach, we suggest a way to understand if the dynamic coupling between ASI and film modes is present or not, with interesting implications for the development of future three-dimensional magnonic applications and devices
Angular-dependent spin dynamics of a triad of permalloy macrospins
No full textWe experimentally and theoretically characterize the angular-dependent microwave response of three-macrospin-vertex structures that can serve as a node in various spin ice lattices. The macrospins consist of patterned permalloy thin films with an elliptical cross section together with an in-plane aspect ratio allowing an Ising-like behavior together with bulk modes as low-frequency excitations in the field range of interest. Various branches of the frequency-magnetic field curves display atypical behaviors and discontinuities, together with softening due to macrospin reversals. The overall behavior observed accurately corresponds to a superposition of the spectra of the individual macrospins. The measured ferromagnetic resonance spectra are in good agreement with theoretical modeling. In particular, they reveal a close correlation between the field direction (relative to the individual macrospins), and the corresponding frequency-magnetic field curve, i.e., between the geometry and the magnetic response
Ferromagnetic resonance in single vertices and 2D lattices macro-dipoles of elongated nanoelements: measurements and simulations
No full textWe report broadband ferromagnetic resonance measurements of the in-plane magnetic field
response of three- and four-fold symmetric vertices formed by non-contacting permalloy
nano-ellipses together with extended lattices constructed from them. Complementing the
experimental data with simulations, we are able to show that, as far as the most intense FMR
responses are concerned, the spectra of vertices and lattices can largely be interpreted in terms
of a superposition of the underlying hysteretic responses of the individual ellipses, as
elemental building blocks of the system. This property suggest that it is possible to understand
the orientation of the individual magnetic dipole moments in a dipole network in terms of
dynamic measurements alone, thereby offering a powerful tool to analyze the alignment
statistics in frustrated systems that are exposed to various magnetic histories
Ferromagnetic resonance in single vertices and 2D lattices macro-dipoles of elongated nanoelements: Measurements and simulations
No full textWe report broadband ferromagnetic resonance measurements of the in-plane magnetic field response of three- and four-fold symmetric vertices formed by non-contacting permalloy nano-ellipses together with extended lattices constructed from them. Complementing the experimental data with simulations, we are able to show that, as far as the most intense FMR responses are concerned, the spectra of vertices and lattices can largely be interpreted in terms of a superposition of the underlying hysteretic responses of the individual ellipses, as elemental building blocks of the system. This property suggest that it is possible to understand the orientation of the individual magnetic dipole moments in a dipole network in terms of dynamic measurements alone, thereby offering a powerful tool to analyze the alignment statistics in frustrated systems that are exposed to various magnetic histories
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