Electric field control of magnetism in nickel with coaxial cylinder structure at room temperature by electric double layer gating

Spin capacitors, which not only store charges but also spins, have been recently proposed based on the surface/interface magnetoelectric effect. The realization of spin capacitors is, however, not straightforward due to the small change of magnetization under normal electric fields in an ordinary capacitor structure. Here we demonstrate electric-field control of the magnetism in Ni/Cu coaxial cylinders in an electric double layer capacitor (EDLC) configuration. The huge electric field effect generated by EDLCs results in a relative magnetization change as large as 18% after charging at a voltage of 2.0 V. Furthermore, the total magnetization change of the device can be enhanced by increasing the number of Ni/Cu wires and surface/bulk ratio. Our first-principles calculations, together with the results from X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy, confirm that the magnetization change in this coaxial cylinder structure is due to the surface magnetoelectric effect, indicating that the proposed electric double layer capacitors with Ni/Cu coaxial cylinders have potential applications in spin capacitors at room temperature.