Takeshi Kawabe

Electric-field-induced changes of magnetic moments and magnetocrystalline anisotropy in ultrathin cobalt films

In this study, the microscopic origins of the voltage-controlled magnetic anisotropy (VCMA) in 3d-ferromagnetic metals are revealed. Using in-situ X-ray fluorescence spectroscopy that provides a high quantum efficiency, electric-field-induced changes in orbital magnetic moment and magnetic dipole Tz terms in ultrathin Co films are demonstrated. An orbital magnetic moment difference of 0.013{mu}B. was generated in the presence of electric fields of +(-)0.2 V/nm. The VCMA of Co was properly estimated by the induced change in orbital magnetic moment, according to the perturbation theory model. The induced change in magnetic dipole Tz term only slightly contributed to the VCMA in 3d-ferromagnetic metals.

Characterization of the magnetic moments of ultrathin Fe film in an external electric field via high-precision X-ray magnetic circular dichroism spectroscopy

The magnetic moments of a Pt|Fe(0.5 nm)|MgO film at an external electric field of in a 0.35 V/nm were characterized by analyzing the X-ray magnetic circular dichroism (XMCD) at the L-edges of Fe using a partial fluorescence yield method with a precision 40 times greater than that in our previous study. The XMCD induced by the electric field was negligible (<0.2%). Furthermore, although an induced orbital magnetic moment seemingly existed, it was within the precision error (0.3%). This paper demonstrates that slight electron doping and/or redistribution without any electrochemical reaction causes voltage-controlled magnetic anisotropy at Fe|MgO interfaces.

Magnetic tunnel junction with Fe(001)/Co phthalocyanine/MgO(001) single-crystal multilayer

A single-crystal multilayer consisting of Fe, cobalt phthalocyanine (CoPc), and MgO was grown on an fcc-MgO(001) substrate. The reflection high-energy diffraction observation showed that the ultrathin fcc-MgO(001) film could be grown on bcc-Fe(001)/CoPc when the thickness of CoPc was less than 0.7 nm (about two molecular layers). A tunnel junction with a bcc-Fe(001)/CoPc/fcc-MgO(001)/bcc-Fe(001) layer achieved a tunnel magnetoresistance of about 20% and an electric field endurance of more than 1 V/nm at room temperature. The novel multilayer in the present study will enable us to advance the frontiers of molecular spintronics.