Magnon-mediated current drag in the semiclassical regime

Abstract

In this Thesis we analyse the phenomenon of a charge current mediated by magnons from one non-magnetic metal layer to another through a ferromagnetic insulator. Using the Boltzmann equation in combination with magnetoelectronic curcuit theory we derive the necessary equations for the interfacial spin and heat currents due to the interaction between electrons and magnons at an interface between a non-magnetic metal and a ferromagnet. Then we analyse magnon transport in a ferromagnetic insulator and find expressions for the magnon spin and heat currents, for the magnon (heat) conductivity and the spin-Seebeck coefficient. We also derive the magnon diffusion length in terms of the relaxation time. As an application of the derived equations we look at a tri-layer structure where a ferromagnetic insulator (Yttrium Iron Garnet) is sandwitched between two non-magnetic metals (Platinum) and predict the ratio of the current mediated from one platinum layer to the other by magnons in the ferromagnet. From this we conclude that, although only of the order 10^−6, the ratio has a maximum when the thickness of the second platinum layer is about the same as the spin diffusion length.