Growth temperature effects on the structural and magnetic properties of ferromagnetic nanostructures self-assembled on vicinal surface Ag(977)
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Universidade Federal de Minas Gerais
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Dissertação de mestrado
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Membros da banca
Edmar Avellar Soares
Luis Eugênio Fernandez Outon
Luis Eugênio Fernandez Outon
Resumo
The use of thin films, and more recently of nanostructures, to optimize physical and
chemical properties of materials is ubiquitous nowadays. In this context, the deposition of
ultrathin films on vicinal surfaces has been an area of great scientific curiosity, given that the
periodic arrangement of substrate steps in nanometric scale can lead to the ordered growth of
nanostructures, and such self-organization has great technological appeal. In particular, low
dimensional ferromagnetic systems have received great attention due to promising applications
in magnetic memory devices and spintronics. In order to improve the understanding of these
systems, here we investigate the effects of the growth temperature on the structural and
magnetic properties of ultrathin iron (Fe) and cobalt (Co) ferromagnetic films on vicinal
Ag(977). A few monolayers (ML) were slowly deposited by molecular beam epitaxy (MBE)
between 0.5 ML and 5.0 ML. In-situ analysis techniques were used, such as low energy electron
diffraction (LEED), scanning tunneling microscopy (STM) and magneto-optical Kerr effect
(MOKE). For Fe/Ag(977) grown at room temperature, in the 2.0 ML to 5.0 ML range, we
observe the formation of elongated nanostructures (“nanowires”) of Fe aligned with the step
edges of the vicinal surface. At 500 K, between 1.0 ML and 3.0 ML, the growth of triangular
structures was observed, most probably with surface alloy formation among the thin film
and the substrate. For Co/Ag(977) samples grown at 500 K, for lower thickness, we observe
the formation of triangular structures, suggesting Co stacking fault (FCC) on the Ag(111)
terraces, and hexagonal structures due to Co-HCP stacking for higher thickness. From the
point of view of magnetic properties, which were investigated by MOKE, we have observed
from a thickness of 3.0 ML Fe on Ag(977) the presence of a distinguished ferromagnetic
signal, when compared to the substrate diamagnetic signal. Nevertheless, for Co/Ag(977) a
ferromagnetic signature was already present from 2.0 ML. Both systems have shown strong
anisotropies and the experimental results indicate that the easy magnetization axis is in-plane
and aligned with the steps, while the hard axis is out-of-plane. Furthermore, the coercive
field strength has a dependence with the in-plane angle (φ) of the applied magnetic field,
with a minimum value when aligned to the steps, which is in line with the nano-structured
arrangement observed by STM.
Abstract
Assunto
Matéria condensada, Física de superfície, Magnetismo
Palavras-chave
Condensed matter, Ag(977) Vicinal surface, Physics of surfaces and interfaces, Magnetism and matter