Large voltage-induced coercivity change in Pt/Co/CoO/amorphous TiOx structure and heavy metal insertion effect

Tomohiro Nozaki,Akio Fukushima,Makoto Konoto,Shingo Tamaru,Hitoshi Kubota,Shinji Yuasa,Takayuki Nozaki

doi:10.1038/s41598-021-00960-w

Tomohiro Nozaki, Akio Fukushima + Show 5 more

Open Access

https://doi.org/10.1038/s41598-021-00960-w

Copy DOI

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 (Hc) change of perpendicularly magnetized Pt/heavy metal/Co/CoO/amorphous TiOx structures. The thin CoO layer in the structure was the result of the surface oxidation of Co. We observed a large voltage-induced Hc change of 20.2 mT by applying 2 V (0.32 V/nm) to a sample without heavy metal insertion, and an Hc 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 TiOx layer could be related to the large voltage-induced Hc change. Furthermore, we demonstrated the separate adjustment of Hc and a voltage-induced Hc change by utilizing both upper and lower interfaces of Co.

Highlights

In response to the high demand for high-speed, low-power-consumption information processing systems, voltage-controlled spintronics devices such as a voltage-controlled magneto-resistive random access memory (MRAM)[1] have attracted great attention
The actual film structure was evaluated from reflection high-energy electron diffraction (RHEED) and cross sectional transmission electron microscope (TEM) analysis
We investigated the voltage-induced Hc change of perpendicularly magnetized Pt/heavy metal/Co/ CoO/amorphous TiOx structures

Summary

Introduction

In response to the high demand for high-speed, low-power-consumption information processing systems, voltage-controlled spintronics devices such as a voltage-controlled magneto-resistive random access memory (MRAM)[1] have attracted great attention. Fcc-Co (111)-based systems are a promising option, on account of its large perpendicular magnetic anisotropy (PMA) and high adjustability. It may achieve a large VCMA coefficient at room temperature. There is room for further improvement through the implementation of an epitaxial film or precise control of the film structure Another advantage of Fcc-Co (111)-based systems is a large interface PMA, which arise at various interfaces[15]. The large interface PMA enables investigation of the voltage effect in a wide range of Co thicknesses These merits make the fcc-Co (111)-based systems attractive for VCMA research.

Methods

Results

Conclusion