The magnetoelectric (ME) effect is one of the methods for electrically controlling the magnetization direction. In this study, we investigated the ME-driven domain wall creep and depinning using a Pt/Co/Au/ME-Cr2O3/Pt thin film. The domain switching process is governed by domain wall propagation rather than the nucleation of reversed domains, similar to a pure ferromagnet. The domain wall velocity v increases exponentially with the ME pressure, that is, the simultaneous application of magnetic H and electric E fields. The v– E curve under a constant H can be scaled by the ME pressure with the assistance of the exchange bias. We determined the depinning threshold, pinning energy scale, and depinning velocity based on the model for the magnetic domain wall creep. Compared with the depinning velocity in various other systems, it was suggested that the ME-driven mechanism could yield a fast domain wall velocity utilizing the low pressure.

We investigate magnetoelectric switching of perpendicular exchange bias with very low coercivity in a Pt/Co/Ir/Cr2O3/Pt epitaxial film. We also optimize the suitable Ir spacer thickness so that the film exhibits the perpendicular exchange bias greater than the coercivity up to the vicinity of the Néel temperature. Main impact of the Ir spacer layer is the significant reduction of coercivity less than 0.5 mT in maintaining both the perpendicular magnetic anisotropy and the perpendicular exchange bias. For the suitable structure, the perpendicular exchange bias was isothermally switched by the gate voltage in combination with the magnetic field. Analysis of the hysteresis of the exchange bias field as a function of the gate voltage suggested that the magnetoelectric coefficient was comparable to the reported value. This implies that the Ir layer does not degrade the efficiency to transfer the magnetoelectrically controlled antiferromagnetic order parameter to the ferromagnetic Pt/Co/Ir trilayer.

Perpendicular exchange bias using magnetoelectric Cr2O3 has an electric-field triggered switching ability, and the thickness limit of the Cr2O3 layer for inducing this bias is a topic of research. In this paper, we investigated the structural, magnetic, and electric properties of Pt/Co/Au/Cr2O3/Pt thin films with a Cr2O3 layer in the thickness range of 5.7 to 25 nm. By using a magnetron sputtering method, a well-crystallized Cr2O3(0001) layer was formed in 5.7-nmthick Cr2O3. All studied films showed perpendicular magnetic anisotropy. The uniaxial magnetic anisotropy energy density increased as the Cr2O3 thickness decreased, and 810±90 kJ/m 3 was obtained for the film with 5.7-nm-thick Cr2O3. Perpendicular exchange bias was evaluated above 80 K, and an exchange anisotropy energy density of 0.30 mJ/m 2 was observed for the film with a 25-nm-thick Cr2O3 at 80 K. The exchange bias could not be observed below 18 nm. Instead, coercivity enhancement, which yields the exchange bias by precisely controlling interfacial exchange coupling, was observed. The electric resistivity was about 5  10 5 •m for the 5.7-nm-thick Cr2O3 layer, which is sufficiently high for magnetoelectric applications.