1,721,007 research outputs found
Footprints of the specific artificial spin ice microstate on the dynamic properties of its spin waves
No full textWe show the results of micromagnetic simulations, where the dynamic
properties of the spin wave (SW) resonances (at zero wavevector) in an
artificial spin ice (ASI) are studied as a function of the magnetic microstate
at remanence (H=0). In particular, we select a few microstates with specific
magnetic charge at an ASI vertex (including a flux-closure vortex one), and,
after calculations by Fourier analysis, look to the corresponding spin wave
spectrum and spin wavefunction profiles [1]. We discuss: (1) the modification
of the nodal lines as a function of the macrospin separation and width,
recognizing the phase-shift peculiar to the magnetic charge at vertex (Fig. 1);
(2) the frequency gap between the edge mode and the fundamental mode; (3)
the role of macrospin density in the array, as well as the macrospin width;
(4) the role of the absolute size of a macrospin (in units of the exchange
length) in determining how rich of modes (and peaks) is the spectrum [2].
We suggest a few experimental techniques (micro-focused Brillouin light
scattering [3], X-ray microscopy [4]), to prove the described predictions.
Our results aim to understand the footprints left in the dynamics by the
specific orientation of the macrospin magnetization at the ASI vertices, so
that a direct control of the SW propagation properties, particularly phaseshifts,
might be pursued through specific macrospin reversals. This control
is of crucial importance in the context of interferometric processing of SW
information carriers, for magnonic logic devices and spin wave computing.
[1] R. Negrello, F. Montoncello, M.T. Kaffash, M.B. Jungfleisch,
G. Gubbiotti, APL Mater. 10, 091115 (2022). [2] Pietro Micaletti and
Federico Montoncello, magnetochemistry 9, 158 (2023). [3] T. Sebastian,
K. Schultheiss, B. Obry, B. Hillebrands and H. Schultheiss, Front. Phys. 3,
35 (2015). [4] Nick Träger, Felix Groß, Johannes Förster, Korbinian Baumgaertl,
Hermann Stoll, Markus Weigand, Gisela Schütz, Dirk Grundler and
Joachim Gräfe, Scientific Reports 10, 18146 (2020)
Spin Waves: versatile, low-dissipation carriers in ferromagnetic systems as a potential source of entanglement
No full textSpin Waves are the coherent oscillations of the magnetic moments of a medium, they do not involve any charge transfer and hence don’t cause Joule dissipation. Even if their fundamental properties are known since decades, their ultimate properties in complex nano-systems are even today a matter of intense investigation both in the theoretical and experimental territories. Their inherent propagation anisotropy is particularly appealing for applications, together with their easy tunability, which comes from Bragg diffraction across the nanostructures and can be controlled by either small magnetic fields or even voltage in multiferroic systems [1]. We review a few spin wave key properties, from a magnetized film, to a lattice of macrospins in an ice-like arrangement (artificial spin ice) and arrays of magnetic vortices. Their intrinsic wave nature, together with the quantization of their energy revealed by light scattering experiments, suggests to realize systems and conditions where spin waves occur as an entangled superposition of otherwise independent states. Following the exposure to tiny magnetic fields or anisotropies introduced in the material by external agents, the superposition breaks down into separate states correlated to the field or anisotropy values [2]. To illustrate the possibility, we discuss spin waves in the vortex state and hybrid spin waves in special ferromagnetic systems, in the perspective of computation and sensing [3].
[1] R. Negrello, F. Montoncello, M. T. Kaffash, M. B. Jungfleisch, and G. Gubbiotti, APL Mater. 10, 091115 (2022).
[2] G. Gubbiotti, M. Madami, S. Tacchi, G. Carlotti, H. Tanigawa, T. Ono, L. Giovannini, F. Montoncello, and F. Nizzoli, Phys. Rev. Lett. 97, 247203 (2006).
[3] Dany Lachance-Quirion, Yutaka Tabuchi, Arnaud Gloppe, Koji Usami, and Yasunobu Nakamura, Appl. Phys. Express 12, 070101 (2019)
Spin waves in configurational antiferromagnetic states: transitions to and from ferromagnetic states
No full textWe study collective spin waves in transversally magnetized chains of thin elliptical dots initially arranged into an antiferromagnetic (AF) configuration. The dispersion relations of the SW as well as the corresponding magnetization precession profiles (eigenvectors) are computed with the dynamical matrix method [1]. We report the peculiar features of AF optical and acoustical spin modes within the effective wavevector model [2], which has been adapted to the present geometry. We investigate the effects of the application of a transverse external field, leading
the system from a perfect AF configuration to the ferromagnetic (FM) state, at a specific transition field. We discuss the mode localization and symmetry, and in particular, we focus on the AF soft mode, its symmetry and its relationship with the instability leading to AF-to-FM transition. We discuss the importance and potential application of the SW propagative properties suddenly changed at the switching from AF to FM. Finally, we present the calculations of spin dynamics concerning a FM-to-AF transition in a chain of ellipses with different width: in this case, the different shape anisotropy of the two ellipses results in different switching fields and hence in a field interval where the AF state is spontaneously attained. We show how this AF field interval can also be tuned by an effective uniaxial anisotropy of one out of two ellipses: this is indicative of any other source of anisotropy (like inverse-magnetostriction, particularly promising for voltage driven magnetic transitions in multiferroics): in this way, we investigate the AF-to-FM transition spin dynamics by varying the effective anisotropy constant of the material. Finally, we show and comment on thepeculiar and remarkable change of slope of the mode dispersion across the AF-to-FM transition, with its implications in the field of magnon-spintronics devices.
References: [1] L. Giovannini, F. Montoncello, and F. Nizzoli, Phys. Rev. B 75, 024416 (2007).
[2] F. Montoncello, S. Tacchi, L. Giovannini, M. Madami, G. Gubbiotti, G. Carlotti, E. Sirotkin, E. Ahmad, F. Y. Ogrin, and V. V. Kruglyak, Appl. Phys. Lett. 102, 202411 (2013)
Spin Waves realizing the classical analog of a quantum state superposition for computation and sensing
No full textSpin Waves are the coherent oscillations of the magnetic moments of a
medium, their propagation does not involve energy dissipation by Joule
effect, and in periodic systems their wave function profile can be nonuniform
and crucially dependent on the (tunable) symmetry of the underlying
magnetization[1]. Their intrinsic wave nature, together with the quantization
of their energy, suggests to use them to implement an entangled state superposition,
which can collapse due to any symmetry breaking in the underlying
magnetization texture[2,3]. The symmetry breaking can result from
the measurement of any external quantity in sensing applications (e.g., a
tiny external field or induced anisotropy) or from an intentional operation
in computing applications[4]. With the help of micromagnetic simulations,
we present an overview of two different situations: spin waves in a
vortex magnetization state (Fig. 1 shows an illustration of a possible state
superposition, exploiting the properties of spin waves in vortex magnetized
rings[5]), and spin waves occurring as hybrids in a lattice of macrospins
(elongated elements). In both cases, we suggest how to address the Bloch
sphere through the complex amplitude of the spin-wave profiles, how to
implement a gate operation which preserves the entanglement, and how to
break the symmetry (i.e., the measurement) and force the system to collapse
in one of the originally irreducible states, producing a result detectable, in
principle, by any space-resolved spectroscopy (e.g., micro-focused Brillouin
light scattering or X-ray microscopy[6,7]).
[1] R. Negrello, F. Montoncello, M.T. Kaffash et al., APL Mater. 10, 091115
(2022). [2] Dany Lachance-Quirion et al., Appl. Phys. Express 12, 070101
(2019). [3] M. Mohseni, V.I. Vasyuchka, V.S. L’vov, A.A. Serga and B. Hillebrands, Communications Physics 5, 196 (2022). [4] C. L. Degen, F. Reinhard, and P. Cappellaro Rev. Mod. Phys. 89, 035002 (2017). [5]
G. Gubbiotti, M. Madami, S. Tacchi, et al., Phys. Rev. Lett. 97, 247203
(2006). [6] T. Sebastian, K. Schultheiss, B. Obry, B. Hillebrands and H. Schultheiss, Front. Phys. 3, 35 (2015). [7] Nick Träger, Felix Groß, Johannes Förster et al., Scientific Reports 10, 18146 (2020)
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
Magnetic normal modes of elliptical NiFe nanorings studied by micro-focused Brillouin light scattering
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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