Flexible Multiferroic Bulk Heterojunction with Giant Magnetoelectric Coupling via van der Waals Epitaxy

Abstract

Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate clamping effect still remains a major hurdle in realizing the ultimate magnetoelectric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric-ferrimagnetic bulk heterojunction on a flexible muscovite via van der Waals epitaxy is adopted. In this study, we investigated the magnetoelectric coupling in a self-assembled BiFeO (BFO)-CoFeO (CFO) bulk heterojunction epitaxially grown on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate clamping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO-CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm·Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance.

Mechanical Strain‐Tunable Microwave Magnetism in Flexible CuFe2O4 Epitaxial Thin Film for Wearable Sensors

“…For further understanding of the epitaxial relationship between the CuFO thin film and the Mica substrate, the in‐plane φ scans are performed on the CuFO (440) and Mica(202) peaks for the CuFO‐80 sample, as shown in Figure c. The sharp peaks of the CuFO film exhibit 6‐fold symmetry with respect to 3‐fold symmetric Mica peaks further indicate that the CuFO film has good crystalline quality and epitaxial nature . The epitaxial relationship between the CuFO film and the Mica substrate can be determined as (111) CuFO //(001) Mica and CuFO //[010] Mica .…”

“…Hence, flexible epitaxial thin film is an essential component of wearable sensors . Recently, some flexible ferromagnetism, ferroelectricity, conductivity, and ME coupling epitaxial thin films have been successfully obtained by using flexible substrate (Mica) or transfer method (peel epitaxial thin films from their hard substrates), such as ITO/Mica, Fe 3 O 4 /Mica, BiFeO 3 ‐CoFe 2 O 4 /Mica, PZT/Mica, BaTi 0.95 Co 0.05 O 3 /Mica, LiFe 5 O 8 , and CoFe 2 O 4 etc . However, the flexible microwave magnetism epitaxial thin films are still scarce up to now.…”

Metal Oxide Nanocomposites: A Perspective from Strain, Defect, and Interface

“…Recently, flexible substrates have been used to grow functional oxide thin films via Van der Waals epitaxy or transfer . Chu and co‐workers reported the growth of BFO:CFO VANs on a flexible muscovite via van der Waals epitaxy . A ME coupling coefficient of 74 mV cm −1 Oe −1 was found in this bulk heterojunction.…”

Van der Waals oxide heteroepitaxy

“…Lately, there is a demonstration of the heteroepitaxy with Pb(Zr,Ti)O 3 , a classic ferroelectric material, on muscovite. 39 An extensive exploration of device performance validated a robust ferroelectric memory device with good flexibility and cyclability. Furthermore, the heteroepitaxy on muscovite provides a solution to show excellent performance of strictive materials, such as piezoelectric Pb(Zr,Ti)O 3 and magnetostrictive CoFe 2 O 4 .…”

“…Thus, there is no misorientation control of vdW oxide heteroepitaxy, implying an Fig. 2 A summary on the current status of vdW oxide heteroepitaxy 31,34,[36][37][38][39][40] Van der Waals oxide heteroepitaxy Y-H Chu important research direction since the anisotropic property is a key feature in most epitaxial thin film system. (4).…”