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Spin-wave discretization in cylindrical permalloy dots -- Presentazione orale by R. Zivieri - Conferenza internazionale
No full textA detailed investigation of the dynamical magnetic properties of arrays of
permalloy disks with radius between 0.1 and 0.5 micron and fixed thickness of
50 nm is presented. The arrays of dots were fabricated using electron beam
lithography and lift-off technique. The Kerr hysteresis loops measured in the
longitudinal configuration showed that the magnetic vortex state [1] is the
ground state of the dots with annihilation and nucleation fields which depend
on the dot radius. Brillouin Light Scattering experiments from spin waves,
exploited in the saturated state, gave evidence of a marked discretization of the
spin wave spectrum with respect to that of the continuous Permalloy film. The
dependence of the frequency of the discrete modes on both the intensity of the
external applied field and the in-plane wave-vector has been measured. The
modes observed at high frequencies are discrete surface magnetostatic waves.
The modes at low frequencies are identified as bulk backward magnetostatic
spin waves and tend to disappear in the Brillouin spectra with increasing the
disk radius. A considerable agreement between the measured frequencies and
the calculated ones according to the Guslienko-Slavin model has been obtained
for the high frequency modes. The low frequency modes have been interpreted in the framework of the formalism of the backward volume modes applied to disks [2].
[1] T. Shinjo, T. Okuno, R. Hassdorf, K. Shigeto, and T. Ono, Science vol.
289, 930 (2000). T. Okuno, K. Shigeto, T. Ono, K. Mibu, and T. Shinjo, J.Magn. Magn. Mater . 240, 1 (2002)
[2] G. Gubbiotti, G. Carlotti, R. Zivieri, F. Nizzoli, T. Okuno and T. Shinjo, J.
Appl. Phys., to be published -- Presentazione orale by R. Zivieri - Conferenza internazional
Dynamic properties of submicron circular permalloy dots -- Presentazione poster by R. Zivieri - Conferenza internazionale
No full textCircular dots of permalloy with appropriate aspect ratio can exhibit a vortex structure with
perpendicular magnetization at the core [1,2]. In this paper, the dynamic properties of some dots
with the above mentioned characteristics, have been
sistematically investigated by Brillouin light
scattering (BLS) from thermally excited spin waves.
Fig.1 shows the comparison between the BLS
spectrum of the continuous permalloy film and that
of circular dots with diameter of 0.2 micron,
recorded in the same experimental conditions.
These spectra give evidence of a marked
discretization of the spin wave spectrum in
agreement with the theoretical prediction of
Guslienko et al. [3]. In fact, instead of the peak
associated to Damon-Eshbach mode measured for
the continuous film, five well resolved peaks are
present on both sides of the spectrum of the
patterned sample. The dependence of the frequency
of these discrete modes on both the intensity of the
external applied field and the in-plane wavector has
been measured. The experimental frequencies have
been compared to those calculated according to the
model proposed in Ref.3. We show that in the
wavevector interval investigated, the frequency of
these discrete modes is dispersionless and the
frequency monotonously increases with the
intensity of the magnetic field. Similar results were
observed by Jorzick et al. in circular permalloy dots
with diameter of 1 and 2 micron.[4]
REFERENCES
[1] T. Shinjo, T. Okuno, R. Hassdorf, K. Shigeto,
and T. Ono, Science 289, 930 (2000)
[2] T. Okuno, K. Shigeto, T. Ono, K. Mibu, and T. Shinjo, Proceeding of the MML01
Conference.
[3] K. Yu Guslienko and A. N. Slavin, J. Magn. Magn. Mater. 215, 576 (2000).
[4] J. Jorzick, S. O. Demokritov, B. Hillebrands, B. Bartenlian, C. Chappert, D. Decanini, F.
Rousseaux, and E. Cambril, Appl. Phys. Lett. 75, 3859, (1999). --Presentazione poster by R. Zivieri - Conferenza internazional
Size-dependent spin wave frequency in submicron cylindrical dots -- Presentazione orale by R. Zivieri - Conferenza internazionale
No full textThin cylindrical dots with submicron diameter support vortex state in remanence [1,2]. In this
paper, the dynamic properties of some dots with the above mentioned characteristics, have been
sistematically investigated by Brillouin light scattering (BLS) from thermally excited spin
waves. Array of cylindrical Ni81Fe19 (Permalloy) alloy dots with thickness of 50 nm and radius
in the range between 0.1 and 0.5 ìm were prepared by means of electron-beam lithography and
evaporation in ultrahigh vacuum using an electron beam gun. For each array the interdot
separation is equal to the dot diameter. Fig.1 shows the BLS spectra for two arrays of cylindrical
dots with radius of 0.1 and 0.5 micron and that of the continuous film. These spectra give
evidence of a marked discretization of the spin wave mode: both the number and the frequency
separation of the modes decreases as the dot radius is increased. In addition, the mode frequency
increases for increasing the radius of the dots and tend toward the spin-wave frequency of the
continuous film. These results are in qualitative agreement with the theoretical model proposed
by Guslienko et al. [3] for tangentially magnetized cylindrical dots. However, this model does
not reproduce the experimental frequencies in a quantitative way even if the agreement is better
for larger dot radius for which the condition L<<R is better verified. Interestingly, we stress that
the bulk standing mode, visible in the spectrum of the continuous film at about 18 GHz, does not
appear in the spectra of the array of dots probably because of the presence of strong static
demagnetizing field inside the dots.
[1] T. Shinjo, T. Okuno, R. Hassdorf, K. Shigeto, and T. Ono, Science 289, 930 (2000).
[2] G. Gubbiotti, G. Carlotti, R. Zivieri, F. Nizzoli, T. Okuno, T. Shinjo, IEEE Trans. on
Magnetics, submitted.
[3] K. Yu Guslienko and A. N. Slavin, J. Magn. Magn. Mater. 215, 576 (2000). -- Presentazione orale by R. Zivieri - Conferenza internazional
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Erratum: Brillouin light scattering investigation of dynamic spin modes confined in cylindrical Permalloy dots
No full textThe quantized mode spectrum of standing spin waves and edge modes in cylindrical Permalloy dots with a radius R in the range between 100 and 500 nm, thickness L550 nm, and separation 2R, is examined from both experimental and theoretical points of view. Brillouin scattering measurements in the Damon-Eshbach geometry give evidence of a marked discretization of the spectra with respect to that of the continuous Permalloy film. The modes can be classified into two distinct families according to their frequency. The upper
one consists of the usual Damon-Eshbach, dipole-exchange modes. The modes belonging to the lower family, instead, oscillate parallel to the applied field and are reminescent of the backward modes of the film. Brillouin measurements performed with the applied field parallel to the transferred spin-wave wave vector, confirm this interpretation. The frequencies of these waves have been calculated using a simple theoretical model including the exchange field. Also, a laterally confined mode belonging to this family is observed and its frequency is independent on the dot radius
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