Multiferroic Microstructure Created from Invariant Line Constraint

TL;DR

This study reveals that finite-size effects in epitaxial multiferroic films lead to a line constraint that governs microstructure formation and induces unique magnetic domain patterns, differing from bulk behavior.

Contribution

It demonstrates that an invariant line constraint determines microstructure in thin multiferroic films, highlighting the importance of finite-size effects in their properties.

Findings

Invariant line constraint explains microstructure features

Finite-size effects induce checkerboard magnetic domains

Microstructure differs from bulk and constrained films

Abstract

Ferroic materials enable a multitude of emerging applications, and optimum functional properties are achieved when ferromagnetic and ferroelectric properties are coupled to a first-order ferroelastic transition. In bulk materials, this first-order transition involves an invariant habit plane, connecting coexisting phases: austenite and martensite. Theory predicts that this plane should converge to a line in thin films, but experimental evidence is missing. Here, we analyze the martensitic and magnetic microstructure of a freestanding epitaxial magnetic shape memory film. We show that the martensite microstructure is determined by an invariant line constraint using lattice parameters of both phases as the only input. This line constraint explains most of the observable features, which differ fundamentally from bulk and constrained films. Furthermore, this finite-size effect creates a remarkable checkerboard magnetic domain pattern through multiferroic coupling. Our findings highlight the decisive role of finite-size effects in multiferroics.