Compositional Investigations on the Spin Thermoelectric Effect in Ta100-xCux/Yttrium Iron Garnet Thin Films

Herein, the performance of spin thermoelectric devices comprising Ta100-xCux/yttrium iron garnet (YIG) films is investigated. Metallic electrodes of Ta100-xCux (x = 2, 3, 4, 5, and 7) are fabricated on high-quality YIG films by magnetron sputtering technique. On each film, an undoped Ta electrode is also fabricated for the sake of precise comparison of spin thermoelectric performance. The hybrid Ta100-xCux/YIG devices thus prepared are examined in a longitudinal geometry for the measurement of thermal voltages (V-t). The experiments show that the voltages generated across the Ta100-xCux films with x = 2, 3, and 4 are higher compared with the ones across pure Ta, whereas it is slightly lower for x = 7 film. Such improvement in V-t is ascribed to an increase in the resistivity of Ta100-xCux that strengthens the spin thermoelectric voltage. However, the surface of TaCu alloy films is observed to become rougher as the Cu ratio increases, which affects the injection of spin current across the interface. Due to the interplay between the resistivity and interfacial roughness of TaCu electrodes, the best thermoelectric response is obtained in the Ta97Cu3/YIG system, which is five times higher than the one obtained for undoped Ta/YIG.