Nano-manipulation of photo-induced ferromagnetism in an epitaxial manganite

The ground state properties of correlated electron systems can be extraordinarily sensitive to external stimuli, such as temperature, strain, and electromagnetic fields. Such pliancy offers abundant platforms for functionally reconfigurable materials. In this work we present a metastable and reversible photo-induced insulator-metal transition in strained films of the doped manganite La2/3Ca1/3MnO3. Using a novel combination of cryogenic scanning near-field optical microscopy, magnetic force microscopy, and ultrafast laser excitation, we demonstrate both “writing” and “erasing” of a metastable ferromagnetic metal phase with nano-scale finesse. By tracking optical conductivity and magnetism at the nano-scale, we demonstrate cooperativity and stability of the photo-induced over a wide range of temperatures. Comparison of our observations with first-principles electronic structure calculations reveals the key role of lattice strain, which can stabilize nearly degenerate charge-ordered insulator and ferromagnetic metal ground states by way of epitaxial engineering. Informed by these findings, we propose a simple Landau theory capturing the rich interplay of strain, charge order, and magnetism to guide ongoing functional engineering of epitaxial manganites and related materials.