We present an alternative measurement technique for the longitudinal spin Seebeck effect (SSE), based on harmonic analysis of the signal measured in the Y3Fe5O12/Pt bilayer. In our experimental setup, we use a harmonic magnetic field and a static thermal gradient in the longitudinal configuration to induce a square-wave SSE signal. By using a phase-sensitive detection technique (lock-in), we can reduce the impact of electrical noise, which improves sensitivity and, through harmonic analysis of the measured signal, decouples in real time the SSE signal from other thermoelectric effects.
A wide frequency range, analog in-phase/quadrature generator was developed for use in synchronous detectors. With the parameters chosen for the realization reported in this Note, it can, in principle, operate from 60 Hz up to 400 kHz. Using good quality sine input, deviations from the 90° phase lag of the quadrature output are not larger than 0.2° in the frequency range between 60 Hz and 100 kHz.
We report a modified method to grow graphene in a single-step process. It is based on chemical vapor deposition and considers the use of methane under extremely adverse synthesis conditions, namely in an open chamber without requiring the addition of gaseous hydrogen in any of the synthesis stages. The synthesis occurs between two parallel Cu plates, heated up via electromagnetic induction. The inductive heating yields a strong thermal gradient between the catalytic substrates and the surrounding environment, promoting the enrichment of hydrogen generated as fragments of the methane molecules within the volume confined by the Cu foils. This induced density gradient is due to thermo-diffusion, also known as the Soret effect. Hydrogen and other low mass molecular fractions produced during the process inhibit oxidative effects and simultaneously reduce the native oxide on the Cu surface. As a result, high quality graphene is obtained on the inner surfaces of the Cu sheets as confirmed by Raman spectroscopy.
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