Flexible Epsilon Iron Oxide Thin Films.

Metastable ε-FeO is a unique phase of iron oxide, which exhibits a giant coercivity field. In this work, we grew epitaxial ε-FeO films on flexible two-dimensional muscovite substrates via quasi van der Waals epitaxy. It turns out that twinning and interface energies have been playing essential roles in stabilizing metastable ε-FeO on mica substrates. Moreover, the weak interfacial bonding between ε-FeO and mica is expected to relieve the substrate clamping effect ubiquitously encountered in films epitaxially grown on rigid substrates, such as SrTiO. It is anticipated that these flexible ε-FeO thin films can serve as a platform for exploring possible interesting emergent physical properties and eventually be integrated as flexible functional devices.