  The ground state properties of correlated electron systems can be
extraordinarily sensitive to external stimuli, such as temperature, strain, and
electromagnetic fields, offering abundant platforms for functional materials.
We present a metastable and reversible photoinduced ferromagnetic transition in
strained films of the doped manganite La(2/3)Ca(1/3)MnO3. Using the novel
multi-messenger combination of atomic force microscopy, 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 nanometer-resolved finesse. By tracking both
optical conductivity and magnetism at the nano-scale, we reveal how spontaneous
strain underlies the thermal stability, persistence, and reversal of this
photoinduced metal. Our first-principles electronic structure calculations
reveal how an epitaxially engineered Jahn-Teller distortion can stabilize
nearly degenerate antiferromagnetic insulator and ferromagnetic metal phases.
We propose a Ginzburg-Landau description to rationalize the co-active interplay
of strain, lattice distortion, and magnetism we resolve in strained LCMO, thus
guiding future functional engineering of epitaxial oxides like manganites into
the regime of phase-programmable materials.
