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Thermal images of the sample with overlaid schematic setup. A microwave antenna excites spin waves in the YIG waveguide, which then propagate along the thermal gradient towards a colder (a) and a hotter (b)region and parallel to a static external field . The temperature difference between the left and right side of the waveguide is created by two Peltier elements.
Temperature dependence of the spin-wave spectrum. (a) Scalar network analyzer measurements of the microwave signal being reflected at the excitation antenna for an external field of and different temperatures. A minimum in the parameter indicates maximum absorption by the YIG stripe. (b) Dependence of the external magnetic field which is needed to compensate the dispersion shift in (a) on the temperature measured at the position of the antenna.
(a) Phase-resolved Brillouin light scattering interference measurements revealing the wavelength reduction in a YIG waveguide with an applied thermal gradient (bottom) in comparison to uniform temperature (top). The interference between light that is scattered inelastically from spin waves and reference light with constant reference phase is measured as a function of the lateral position at the waveguide. A high (low) interference signal is indicated by white (black) color. Spin waves are excited at x = 0 mm and propagate along the x direction. (b) Comparison between extracted values of the experimentally observed spin-wave wavelength (symbols) and calculated wavelength values based on the measured temperature along the stripe (lines) for uniform temperature (black) and an applied thermal gradient (pale red). (c) Calculated spin-wave dispersion relations for two different positions. The temperature induced frequency shift of the curves causes an increase in the spin-wave wave vector and hence a wavelength reduction.
(a) Brillouin light scattering measurements of the spin-wave reflection in a thermal gradient. The spatial spin-wave intensity distribution in a YIG waveguide is shown for uniform temperature (top) and increasing temperature (bottom) along the spin-wave propagation direction. White (black) color indicates high (low) spin-wave intensity. Spin waves are excited at x = 0 mm and propagate along the x direction. (b) Calculated spin-wave dispersion relations for a position near the antenna (dark blue) and at a distance of 3.5 mm to the antenna (pale red) illustrating the underlying mechanism of the spin-wave reflection.
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