Influence of interface layer insertion on the spin Seebeck effect and the spin Hall magnetoresistance of Y3Fe5O12 /Pt bilayer systems

Abstract

We observe significantly enhanced spin Seebeck effect (SSE) and spin Hall magnetoresistance (SMR) values by inserting 0.3--0.6-nm-thick layers of magnetic materials with different composition (Cr, ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$, ${\mathrm{Co}}_{90}{\mathrm{Fe}}_{10}$, ${\mathrm{Fe}}_{50}{\mathrm{Co}}_{50}$, and Fe) at the ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$/Pt interface. To study the actual magnetic state of these insertion layers, we, then, investigated the magnetization of these layers via generalized magneto-optical ellipsometry. Magnetic insertion layers in this thickness range did not exhibit a measurable magnetization, even though our method should have detected even a small fraction of the bulk magnetization value for the utilized materials easily. Therefore, the observed SSE and SMR enhancement generated by the insertion of thin magnetic material layers did not result from a net interface magnetization but might, instead, be related to the paramagnetic state of the inserted layers.