Abstract

Magnetization reversal induced by an electric field in multiferroic materials has been extensively investigated because it can be applied to ultra-low-power voltage-write magnetic-read-out memory devices. Co substitution in BiFeO₃ (BiFe_0.9Co_0.1O₃; BFCO) destabilizes the cycloidal spin modulation and generates a canted collinear spin state with a non-zero saturation magnetization [1]. We have examined the magnetic and ferroelectric domain structures of BFCO thin films before and after polarization switching using piezoresponse force microscopy (PFM) and magnetic force microscopy (MFM), and clarified how the magnetoelectric response is determined by the polarization switching pathways, i.e., 71°, 109°, and 180° [2]. In the case of (110)_pc-oriented BFCO/SrTiO₃ (110) films, we demonstrated that 109° polarization switching under an electric field along [1-10]_pc deterministically reversed the out-of-plane magnetization component. This provides an in-plane-write/out-of-plane-read configuration highly advantageous for device applications [3]. We have also examined the ferroelectric and magnetic domains of BFCO nanodots fabricated by deposition through an anodized porous alumina mask. PFM and MFM confirmed that 60-nm-diameter dots are single-domain in both states, whereas 190-nm dots are multidomain, and the comparison of the two domain patterns indicates strong magnetoelectric coupling [4]. More recently, scanning NV magnetometry, free from the tip stray field inherent to MFM, provided quantitative stray-field maps of individual 190-nm BFCO nanodots and revealed reversal of the net magnetization upon electric-field poling [5]. Such insights into ferroelectric and ferromagnetic domains are essential for the design of high record-density BFCO memory devices.

References

[1] H. Hojo et al., Adv. Mater., 29, 1603131 (2017).
[2] K. Shigematsu and M. Azuma, Appl. Phys. Express 19, 040101(2026).
[3] T. Itoh et al., Adv. Mater. 37, 2419580 (2025).
[4] K. Ozawa et al., ACS Appl. Mater. Interfaces 16, 20930 (2024).
[5] K. Lee et al., Sci. Adv. 12, eaec2861 (2026).

Biography

Dr. Kei Shigematsu obtained his Bachelor and Master degrees from The University of Tokyo, Japan, and obtained his Ph.D. from Tokyo Institute of Technology, Japan in 2015. From 2015 to 2016, he served as a researcher at the PIIF Kanagawa Academy of Science and Technology, Japan. From 2016 to 2018,  he is a specially appointed assistant professor at Laboratory for Materials and Structures, Institute of Science Tokyo, Japan. Currently, he is an assistant professor at Laboratory for Materials and Structures, Institute of Science Tokyo, Japan. His research interests manily focused on synthesis, fabrication, and nanofabrication of perovskite oxides and related compounds, and invesigating related magnetic, electric, electric conduction, dielectric, ferroelectric, and optical properties.

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