Large voltage-induced coercivity change in Pt/Co/CoO/amorphous TiOx structure and heavy metal insertion effect
Tomohiro Nozaki, Shingo Tamaru, Makoto Konoto, Takayuki Nozaki, Hitoshi Kubota, Akio Fukushima, Shinji Yuasa
Abstract
Abstract There is urgent need for spintronics materials exhibiting a large voltage modulation effect to fulfill the great demand for high-speed, low-power-consumption information processing systems. Fcc-Co (111)-based systems are a promising option for research on the voltage effect, on account of their large perpendicular magnetic anisotropy (PMA) and high degree of freedom in structure. Aiming to observe a large voltage effect in a fcc-Co (111)-based system at room temperature, we investigated the voltage-induced coercivity ( H c ) change of perpendicularly magnetized Pt/heavy metal/Co/CoO/amorphous TiO x structures. The thin CoO layer in the structure was the result of the surface oxidation of Co. We observed a large voltage-induced H c change of 20.2 mT by applying 2 V (0.32 V/nm) to a sample without heavy metal insertion, and an H c change of 15.4 mT by applying 1.8 V (0.29 V/nm) to an Ir-inserted sample. The relative thick Co thickness, Co surface oxidation, and large dielectric constant of TiO x layer could be related to the large voltage-induced H c change. Furthermore, we demonstrated the separate adjustment of H c and a voltage-induced H c change by utilizing both upper and lower interfaces of Co.