doctoralThesis
Efeitos termoelétricos em bicamadas de Co2FeAl/W com anisotropias uniaxial e cúbica
Fecha
2021-04-26Registro en:
LOPES, Marcus Vinícius Pinheiro. Efeitos termoelétricos em bicamadas de Co2FeAl/W com anisotropias uniaxial e cúbica. 2021. 92f. Tese (Doutorado em Física) - Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte, Natal, 2021.
Autor
Lopes, Marcus Vinícius Pinheiro
Resumen
The conversion of temperature gradients applied to magnetic materials into electrical currents has
been the subject of study due to its importance in the possibility of constructing devices that take
advantage of it. The application of these temperature differences generates electrical responses
due to the production of spin and charge currents that gave rise to an area of spintronics, the
spin caloritronics. From the charge current it is possible to measure the thermoelectric voltage
in magnetic materials, produced by the direct conversion of the temperature gradient into
electrical voltage. In this work, this thermovoltage is mainly associated with two phenomena, the
spin Seebeck (SSE) and anomalous Nernst (ANE) effects. Both are investigated in samples of
Co2FeAl/W (CFA/W) grown on silicon (Si) and gallium arsenide (GaAs) substrates. The samples
were prepared by magnetron sputtering with the substrate under to distinct temperature conditions
during deposition, from 300 K up to 773 K. The bilayers were deposited onto oriented substrates
in order to induce magnetocrystalline anisotropy, thus allowing the obtainment of systems with
an overlap of anisotropies such as uniaxial and cubic. The samples were characterized from the
structural and magnetic point of views. Specifically, the structural characterization was performed
by X-ray diffractometry (XRD), while the quasi-static magnetic behavior was obtained through
magnetization curves measured using a Vibrating Sample Magnetometer (VSM). Thermoelectric
response was explored via longitudinal Spin Seebeck effect (LSSE). In this configuration, the
temperature gradient is normal to the plane of the film, and the external magnetic field lies in
the plane. Then, the thermoelectric voltage is measured with electrical contacts fixed in the film
plane. Computer simulations were also carried out using the adapted Stoner-Wohlfarth model,
which together with the experimental data show that the thermoelectric response of the samples
is the result of the interaction between the uniaxial and cubic contributions of magnetocrystalline
anisotropy. The results place CFA grown onto GaAs substrate as a promising candidate for active
elements in spintronic devices.