Electrical detection of spin waves with complex mode profiles

The modern complementary metal oxide-semiconductor (CMOS) technology may reach their physical limits in the next decade. To be able to continue to improve the device performance, and to further lower the energy cost per operation might require the introduction of new and disruptive technologies. Spin waves are collective low-energy excitation of spins in ferromagnetic materials. Spintronic devices based on spin waves are promising to complement the CMOS transistor technology due to their high potential for significant power and area reduction per computing throughput. Hence, the understanding of the spin-wave mode formation, their propagation properties, and the detection schemes are of high interest for the development of such technologies. This work is focused on studying the emission of spin waves in different magnetic stacks by the Oersted field created by rf currents flowing through inductive wire antenna of various designs. Two detection scheme of spin waves were implemented: the first one is based on the generation of an electrical rf current in a wire antenna by the dipolar oscillating magnetic field associated with the spin waves. In the second case, a dc voltage is over the magnetic waveguide length as a result of the generation of charge currents in an adjacent heavy metal layer via inverse spin Hall effect (ISHE). It is shown that straight wire emitting antenna exhibits a typical spin-wave transmission spectrum, within the frequency band given by the ferromagnetic resonance and the frequency limit associated to the antenna excitation efficiency. However, in case of S-shaped emitting antenna the transmission characteristic shows frequency ranges within the spin-wave band of no signal detection. The performed micromagnetic simulations demonstrated that these gaps are related to the generation of spin waves with non-uniform spatial patterns which are poorly detected by straight wire antennas. To overcome the low detection efficiency of spin waves with complex mode patterns by wire antennas, we proposed to use the inverse spin Hall effect - which is less sensitive to mode profile – to evidence the spin waves. A mask set has been designed and used for device fabrication using material deposition via sputtering technique, optical lithography, and patterning by metal lift-off. The devices were based on different combinations of heavy metals (W, Ta) and magnetic layers (Py, CoFeB, Ni, FeGa). A mixed RF-DC experimental setup was developed together with Labview routine to automate electrical measurements, as well as codes for the data analysis. It is shown that the devices based on a CoFeB / W stack present the highest output ISHE voltage at the same input power, furthermore, it is demonstrated that the ISHE can be used to detect the spin waves with complex mode patterns.