Seminários

Título: 

Spin-wave transmission within Neel walls 

 

Resumo: 

Magnonics is an emerging research field in which spin-waves are used

for information transmission and processing. The data can be encoded
either in the amplitude or the phase, and the absence of charge
transport eliminates Joule losses. Spin-wave propagation is usually
done in geometrically patterned structures that require the continuous
application of an external magnetic field, which jeopardizes its
efficiency [1]. Magnetic domain walls as propagation channels have
been proposed [2,3] as they exist in remanent magnetic states. As
boundary regions, domain walls act as potential wells, thus confining
the spin-waves within its width. We have studied, through
micromagnetic simulations [4], the spin-wave transmission along a 180o
Néel wall in a 10 μm x 1 μm permalloy slab with longitudinal periodic
boundary conditions. We performed an out-of-plane excitation in a 20
nm wide antenna at its center. It has shown that up to 2 GHz
spin-waves are strongly confined within the wall width and, above that
frequency, the wave starts to spread to the uniform domains. The
dispersion relation for the confined waves resembles a
magnetostatic-dominated Damon-Eschbach [5] mode with positive group
velocity. This was expected as the Néel wall has uncompensated
magnetic charges that give rise to a strong magnetostatic field inside
the wall. The Néel wall is usually found in Landau-domain
configurations in nanostructures. Experimentally, the Landau structure
is very hard to achieve as small fields are enough to irreversibly
saturate the structure, as we have shown through hysteresis
simulations, along with SQUID and MOKE magnetometry experiments. To
overcome that, we have fabricated a 10 μm wide rectangular permalloy
structure that gradually shrinks to a 5 μm end in one side [3] by
electron-beam lithography. An alternate exponentially decaying field
is transversely applied to reproducibly obtain the Landau
configuration, as confirmed by Kerr microscopy images. We are
currently performing ferromagnetic resonance experiments in these
structures. This study is aimed to evaluate the suitability of these
spin-waves for magnonic applications.

 

[1] E.ALBISETTI, D.PETTI, M.MADAMI, et al. Nanopatterning
spin-textures: A route to reconfigurable magnonics. AIP Advances,
2016.
[2] F.GARCIA-SANCHEZ, P.BORYS, R.SOUCAILLE et al. Narrow Magnonic
Waveguides Based on Domain Walls. Physical Review Letters, 2015.
[3] K.WAGNER, A.KAKAY, K.SCHULTHEISS, et al. Magnetic domain walls as
reconfigurable spin-wave nanochannels. Nature Nanotechnology, 2016.
[4] VANSTEENKISTE, ARNE, LELIAERT, et al. The design and verification
of MuMax3. AIP Advances, 2014.
[5] R.DAMON, J.ESHBACH. Magnetostatic Modes of a Ferromagnetic Slab.
Journal of Applied Physics, 1960.