Creating a Ferromagnetic Ground State with High T_c in a Paramagnetic Alloy Through Non-Equilibrium Nanostructuring

Materials with strong magneto-structural coupling have complex energy landscapes featuring multiple local ground states, thus making it possible to switch among distinct magnetic-electronic properties. However, it is usually impossible to access these energy minima by applying external stimuli to the system in equilibrium state. Here, we report that a robust ferromagnetic ground state with <i>T</i>_c above room temperature can be created in an initially paramagnetic alloy by nanostructuring with strain. We transformed bulk chemically-disordered FeRh alloys into a nanoporous structure with a topology of a few nanometer-sized ligaments and nodes by non-equilibrium dealloying process. Magnetometry and Mössbauer spectroscopy revealed the co-existence of two magnetic ground states, a conventional low-temperature spin glass and a hitherto-unknown robust ferromagnetic phase. The emergence of ferromagnetic phase is validated by DFT calculations, showing that local tetragonal distortion induced by surface stress favors ferromagnetic ordering. Our study provides a route to reach for conventionally inaccessible magnetic states in phase diagram and induce a complete on/off ferromagnetic-paramagnetic transition over a broad temperature range.