Efeitos termoelétricos em bicamadas de Co2FeAl/W com anisotropias uniaxial e cúbica

Abstract

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.