Investigation of the unidirectional spin heat conveyer effect in a 200 nm thin Yttrium Iron Garnet film.

Olga Wid,Stuart S. P. Parkin,Otwin Breitenstein,Alexander Müller,Jan Bauer,Georg Schmidt

doi:10.1038/srep28233

Abstract

We have investigated the unidirectional spin wave heat conveyer effect in sub-micron thick yttrium iron garnet (YIG) films using lock-in thermography (LIT). Although the effect is small in thin layers this technique allows us to observe asymmetric heat transport by magnons which leads to asymmetric temperature profiles differing by several mK on both sides of the exciting antenna, respectively. Comparison of Damon-Eshbach and backward volume modes shows that the unidirectional heat flow is indeed due to non-reciprocal spin-waves. Because of the finite linewidth, small asymmetries can still be observed when only the uniform mode of ferromagnetic resonance is excited. The latter is of extreme importance for example when measuring the inverse spin-Hall effect because the temperature differences can result in thermovoltages at the contacts. Because of the non-reciprocity these thermovoltages reverse their sign with a reversal of the magnetic field which is typically deemed the signature of the inverse spin-Hall voltage.

Highlights

In 2013 An et al have shown that by the excitation of nonreciprocal spin waves, so-called Damon-Eshbach modes (DEM), in a 400 μm thick Yttrium Iron Garnet (YIG) crystal heat can be transported independent from existing temperature gradient[1]
We clearly observe that as soon as spin wave modes are excited no matter whether in the DEM or in the BVM geometry the magnons heat the yttrium iron garnet (YIG) causing a heating profile that decays away from the waveguide corresponding to the damping of the magnons
At this field the amplitude of the Ferromagnetic resonance (FMR) measurement is high in the DEM geometry and maximum in BVM geometry

Summary

Experimental Setup

As the magnons are damped along the direction of propagation the magnitude of the transfer is smaller further away from the waveguide leading to a decay of the temperature difference with the magnon intensity Moving to the maximum intensity of the DEM (position 2, Fig. 3(b,c)) yields a much bigger increase in temperature but here the difference image clearly shows an antisymmetric temperature profile extending over several mm across and beyond the antenna. This heating does not change during a field reversal and can be eliminated from the measurements by using the difference image between opposite magnetic fields. It should again be noted that here the two difference images show either a positive difference or a negative difference while in the case of the DEM the difference is always antisymmetric showing both positive and negative values

Discussion

Methods