41 research outputs found
Spin excitations of magnetic vortices in ferromagnetic nanodots
No full text---Spin excitations of the magnetic vortex state in ferromagnetic nanodots are measured using Brillouin light scattering. Arrays of permalloy dots with 800-nm diameter and 60-nm thickness were fabricated by means of electron beam lithography and lift-off procedures. Two excitation modes are observed experimentally in the vortex state. One mode, at ∼12 GHz, decreases slightly in frequency to 11 GHz as an in-plane magnetic field is applied. The lower mode, at ∼8 GHz, is almost independent of applied field strength. Numerical and analytical calculations of the dynamic magnetization based on the Landau-Lifshitz equation of motion allows us to identify the higher and lower frequency modes as corresponding to dipole-dominated spin excitations localized inside the dot and at the dot edges, respectively
Low-frequency vortex dynamic susceptibility and relaxation in mesoscopic ferromagnetic dots
No full textMagnetostatic Contribution to Perpendicular Magnetic Anisotropy Constant of Inhomogeneous Films
No full text
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
Thermal stability of the magnetization following thermomagnetic writing in perpendicular media
No full textSize-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
