Thickness dependence of transverse thermoelectric voltage in Co₄₀Fe₆₀/YIG magnetic junctions

Measurements of transverse thermoelectric voltage were carried out in Co₄₀Fe₆₀ (CoFe)/Yttrium-Iron-Garnet (YIG) magnetic junctions, using the CoFe film as the spin detector. An unusual dependence of the voltage on the CoFe thickness was observed in the in-plane magnetized (IM) configuration; the junction with a relatively thick CoFe layer (40 nm) exhibits positive signals, whereas the junctions with a thinner CoFe layer (7–10 nm) exhibit negative signals. To find the origin of the behavior, we compare the voltage signals in the CoFe/YIG and CoFe/GGG systems in the IM configuration as well as perpendicularly magnetized (PM) configuration. Furthermore, the anomalous Hall effect was also measured in the Hall-bar shaped CoFe films. The experimental results suggest that the observed thickness dependence of the voltage is attributed to the combination of the inverse spin Hall effect (ISHE) and the anomalous Nernst effect (ANE) in the CoFe layers; the former shows a negative voltage and its contribution gradually increases with decreasing the CoFe thickness, whereas the latter shows a positive and mostly thickness independent voltage. The competition between the ISHE and ANE contributions results in the observed peculiar CoFe-thickness dependence of the transverse thermoelectric voltage.