Reversible change in the oxidation state and magnetic circular dichroism of Fe driven by an electric field at the FeCo/MgO interface

Abstract

The influence of an electric field on an ultrathin FeCo film was investigated by x-ray absorption spectroscopy and magnetic circular dichroism. Measurements were done on sub-millimeter sized pillars, with partial fluorescence yield detection. Fe L2,3 absorption spectra revealed that partial oxidation of Fe occurred during the microfabrication. The oxidation state could be reversibly controlled by an electric field, which also induced variations of the dichroic signal. These results show that electrochemical phenomena may influence the magnetism at a ferromagnet/insulator interface.

Research Update: Magnetoionic control of magnetization and anisotropy in layered oxide/metal heterostructures

“…16,19,21 Recently, an increasing number of reports points towards an influence of interfacial chemistry. 15,18,20,22,[25][26][27][28][29] The background is that the applied electric field, besides capacitive charging, can induce charge-transfer reactions leading to a reversible change of the oxidation state of, e.g., Fe or Co species. 20,26,29 Magnetic changes based on such electrochemical reactions have recently been denominated magnetoionic (MI) effect.…”

Large time-dependent coercivity and resistivity modification under sustained voltage application in a Pt/Co/AlOx/Pt junction

“…A viable candidate for such a process is the electromigration of oxygen vacancy defects in the dielectric. This mechanism has been suggested to occur in similar devices, 4,7,8,11 and was confirmed to affect the perpendicular magnetic anisotropy at Fe/MgO interfaces. 11 Moreover, electromigration of oxygen vacancies is known to occur in amorphous AlOx barriers, 15 causing soft dielectric breakdown at high electric fields, similar to the behavior observed in Figure 3(c).…”

“…6 The magnitude, symmetry, and timescale of the observed effect differ significantly between experiments, suggesting that physics beyond the charging of an ideal capacitor play a role. [7][8][9] Notably, it has been proposed that the perpendicular magnetic anisotropy arising from Co-O hybridization at the magnet-insulator interface 10 can be directly affected by a voltage-induced migration of oxygen vacancies, 11 resulting in strong voltage-induced anisotropy modifications. 9 Here, we measure the coercive field and leakage current as a function of time under sustained electric field, using Kerr microscopy on a perpendicularly magnetized Pt/Co/AlOx/Pt junction.…”

Electric field effect on magnetism in metallic ultra-thin films

“…This can be one reasonable explanation for the experiment. Another possibility is the oxidation-reduction reaction by the application of the electric field [25,26]. The negative V G is in the direction of the oxidation reaction, which should reduce T C and the magnetic moment of the Co layer.…”

“…As another candidate, the electric field modulation of the uniaxial perpendicular magnetic anisotropy (PMA) caused by the Rashba effect at the interface between the two different materials, e.g., a FM metal and nonmagnetic metal or insulator, has been theoretically proposed [24]. Furthermore, the voltage-driven oxidation-reduction reaction or O 2− migration in the FM/oxide bilayer is known to be another source for altering the magnetic properties of a FM [25,26]; however, this effect is much slower than the electron charging effect.…”