Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on the spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate clamping effect still remains as a major hurdle in realizing the ultimate magnetoelectric coupling. To overcome this obstacle, an alternative strategy of fabricating selfassembled

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... magnetic bulk heterojunction on flexible muscovite via the van der Waals epitaxy is adopted. In this study, we investigated the magnetoelectric coupling in selfassembled BiFeO 3 (BFO)-CoFe 2 O 4 (CFO) bulk heterojunction epitaxially grown on flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedding in the 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 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 remarkable ME heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance. KEYWORDS: Magnetoelectric · bulk heterojunction · clamping effect · van der Waals epitaxy · flexible