Spin Pumping and Inverse Spin Hall Effect in Yttirium Iron Garnet/platinum Hetero-structures
Magnons, which are the quanta of spin waves, are potential candidates for data transfer and processing of spin information in spintronics. Magnons can be excited by a microwave source and propagate in magnetic insulators like yttrium iron garnet (YIG, Y3 Fe5 O12 ) over macroscopic distances. This opens up the possibility of insulator-based spintronic circuits, operating with spin currents entirely decoupled from charge carriers and accompanied parasitic heating. The combination of spin pumping and the inverse spin Hall effect (ISHE) turned out to be excellent candidates for this purpose. In my talk, I will present results on the influence of processing of the YIG surface on the spin pumping efficiency and show a direct application of the obtained results: the direct detection of magnon spin transport by a combination of spin pumping and ISHE.
We succeeded in improving the ISHE signal strength by a factor of more than 150 using a combination of “piranha” etch (a mixture of H2 SO4 and H2 O2) and in-situ O+ /Ar+ plasma treatment in comparison to standard ultrasonic cleaning. The combined processing by “piranha” etch and heating at 500° C yields a comparable enhancement of the spin pumping efficiency (by a factor of 104). In the second part of my talk I will focus on the direct detection of magnon spin transport by a combined method of spin pumping and ISHE, for which an optimal spin pumping efficiency is indispensable. We excite spin-wave packets in an YIG waveguide by a microwave source and detect it 3 mm apart by an attached Pt layer as a delayed ISHE voltage pulse. The delay appears due to the finite spin-wave group velocity and proves the magnon spin transport. In addition, the contribution of secondary excited magnons to the ISHE voltage is measured and estimated theoretically. The field dependent measurements shown that the spin pumping efficiency in YIG/Pt bi-layers does not depend on the spin-wave wavelength.
We acknowledge the financial support by Deutsche Forschungsgemeinschaft (CH 1037/1-1) and by the Grant No. ECCS-1001815 from National Science Foundation of the USA.