Dielectric and magnetic characterizations of capacitor structures with an ionic liquid/MgO barrier and a ferromagnetic Pt electrode

D Hayakawa,T Hirai,K Miwa,D Chiba,A Obinata,S Ono,T Koyama

doi:10.1063/1.4967343

Abstract

The dielectric and magnetic properties of electric double layer (EDL) capacitor structures with a perpendicularly magnetized Pt/Co/Pt electrode and an insulating cap layer (MgO) are investigated. An electric field is applied through a mixed ionic liquid/MgO barrier to the surface of the top Pt layer, at which the magnetic moment is induced by the ferromagnetic proximity effect. The basic dielectric properties of the EDL capacitor are studied by varying the thickness of the MgO cap layer. The results indicate that the capacitance, i.e., the accumulated charge density at the Pt surface, is reduced with increasing the MgO thickness. From the MgO thickness dependence of the capacitance value, the effective dielectric constant of the ionic liquid is evaluated. Almost no electric field effect on the magnetic moment, the coercivity, or the Curie temperature is confirmed in the top Pt layer with the thickness of 1.3 nm, regardless of the presence or absence of the MgO cap layer, whereas the a clear change in the magnetic moment is observed when the top Pt layer is replaced by a Pd layer of 1.7 nm.

Highlights

The electric field effect on magnetism has recently drawn attention in the field of materials science as well as potential application for a magnetic recording technique.[1]
In a capacitor structure consisting of a magnetic electrode, an insulator layer, and a counter electrode, the ferromagnetism in the magnetic electrode can be switched on and off reversibly and isothermally through the application of a gate voltage V G between both electrodes.[2,3,4]
We focus on the electric double layer (EDL) capacitor with a Pt electrode, where a magnetic moment is induced owing to the proximity effect from an adjacent ferromagnetic Co underlayer

Summary

Introduction

The electric field effect on magnetism has recently drawn attention in the field of materials science as well as potential application for a magnetic recording technique.[1]. To investigate the accumulated charge density at the Pt surface, the capacitance of the fabricated capacitors is carefully measured as a function of the MgO cap thickness. Through this experiment, the ratio of the dielectric constant to the effective thickness of the EDL is determined. The ratio of the dielectric constant to the effective thickness of the EDL is determined In both the EDL capacitors with or without the MgO cap layer, almost no electric field effect on magnetism in the 1.3-nm-thick Pt layer, at the surface of which the magnetic moment is expected to be induced, is observed

Methods

Results

Conclusion