Magnetoelectric switching of perpendicular exchange bias in Pt/Co/α-Cr₂O₃/Pt stacked films

We report the realization of magnetoelectric switching of the perpendicular exchange bias in Pt/Co/α-Cr₂O₃/Pt stacked films. The perpendicular exchange bias was switched isothermally by the simultaneous application of magnetic and electric fields. The threshold electric field required to switch the perpendicular exchange bias was found to be inversely proportional to the magnetic field, which confirmed the magnetoelectric mechanism of the process. The observed temperature dependence of the threshold electric field suggested that the energy barrier of the antiferromagnetic spin reversal was significantly lower than that assuming the coherent rotation. Pulse voltage measurements indicated that the antiferromagnetic domain propagation dominates the switching process. These results suggest an analogy of the electric-field-induced magnetization with a simple ferromagnet.Kentaro Toyoki, Yu Shiratsuchi, Atsushi Kobane, Chiharu Mitsumata, Yoshinori Kotani, Tetsuya Nakamura, and Ryoichi Nakatani, Appl. Phys. Lett. 106, 162404 (2015); https://doi.org/10.1063/1.4918940

Robust magnetic domain of Pt/Co/Au/Cr₂O₃/Pt stacked films with a perpendicular exchange bias

Magnetic domain pattern and magnetic domain wall motion are particularly important to understand the magnetization process. Here, we investigated the magnetization process of perpendicularly exchange-biased Pt/Co/Au/Cr₂O₃/Pt stacked films based on observations of the magnetic domain. In particular, in contrast to previous studies which use fully exchange-biased state, we used the bi-exchange-biased state. We found that the magnetic domain pattern at the remanent state was robust against magnetic-field cycling, which is relevant to the absence of the training effect. The magnetization process was followed by domain wall propagation in the increasing branch of the magnetization curve. In the decreasing branch, both nucleation of the reversed domain and domain wall propagation were involved. The former was accompanied by latency, suggesting that thermal activation played a significant role in the nucleation of the reversed domain.Yu Shiratsuchi, Saori Yoshida, Hiroaki Yoshida, Yoshinori Kotani, Kentaro Toyoki, Ryoichi Nakatani, Chiharu Mitsumata, and Tetsuya Nakamura, Journal of Applied Physics 127, 153902 (2020); https://doi.org/10.1063/5.0002240

Antiferromagnetic domain wall creep driven by magnetoelectric effect

We observed the magnetoelectric induced domain wall propagation in a Pt/Co/Au/Cr₂O₃/Pt stacked thin film based on magnetic domain observations using scanning soft X-ray magnetic circular dichroism microscopy. The antiferromagnetic (Cr₂O₃) domain wall velocity was estimated by a quasi-static approach using a pulsed voltage. At a pulse voltage amplitude of -12 V, corresponding to an electric field of -8.0 × 10²kV/cm, the domain wall velocity was very low, at 0.3 m/s. The domain wall velocity increased with increasing voltage amplitude, reaching 22 m/s at -20 V (-1.3 × 10³kV/cm). The change in the domain wall velocity with the applied voltage amplitude indicates the creep motion of the domain wall. Using a phenomenological model, we estimated the domain wall depinning energy, and found that the bulk and interface terms of the magnetic anisotropy affect the effective magnetic field to the same degree, suggesting that the magnetic domain wall motion may be controllable by the antiferromagnetic layer thickness.Yu Shiratsuchi, Hiroaki Yoshida, Yoshinori Kotani, Kentaro Toyoki, Thi Van Anh Nguyen, Tetsuya Nakamura, and Ryoichi Nakatani, APL Materials 6, 121104 (2018); https://doi.org/10.1063/1.5053928

Observation of the magnetoelectric reversal process of the antiferromagnetic domain

We investigated the switching process of the perpendicular exchange bias, which is driven by the magnetoelectric effect, by conducting magnetic domain observations using scanning soft X-ray magnetic circular dichroism microscopy. Isothermal and simultaneous application of magnetic and electric fields switches the perpendicular exchange bias polarity. The switching process proceeds by the nucleation and growth of reversed domains. The correspondence among the ferromagnetic/antiferromagnetic domains and exchange bias polarity indicates that interfacial antiferromagnetic spin/domain reversal is responsible for the magnetoelectric switching of the perpendicular exchange bias polarity.Yu Shiratsuchi, Shunsuke Watanabe, Hiroaki Yoshida, Noriaki Kishida, Ryoichi Nakatani, Yoshinori Kotani, Kentaro Toyoki, and Tetsuya Nakamura, Appl. Phys. Lett. 113, 242404 (2018); https://doi.org/10.1063/1.5053925

Magnetic anisotropy driven by ligand in 4d transition metal oxide SrRuO3

The origin of magnetic anisotropy in magnetic compounds is a longstanding issue in solid state physics and nonmagnetic ligand ions are considered to contribute little to magnetic anisotropy. Here, we introduce the concept of ligand driven magnetic anisotropy in a complex transition-metal oxide. We conducted X ray absorption and X ray magnetic circular dichroism spectroscopies at the Ru and O edges in the 4d ferromagnetic metal SrRuO3. Systematic variation of the sample thickness in the range below 10 nm allowed us to control the localization of Ru 4d t2g states, which affects the magnetic coupling between the Ru and O ions. We found that the orbital magnetization of the ligand induced via hybridization with the Ru 4d orbital determines the magnetic anisotropy in SrRuO3