Creating A Ferromagnetic Ground State with Tc Above Room Temperature in A Paramagnetic Alloy Through Non-equilibrium Nano-structuring.

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, these energy minima are rarely accessible by a mere application of an external stimuli to the system in equilibrium state. Here, we report that a ferromagnetic ground state, with Tc above room temperature, can be created in an initially paramagnetic alloy by non-equilibrium nano-structuring. By dealloying process we transformed bulk chemically-disordered FeRh alloys into a nanoporous structure with a topology of a few nanometer-sized ligaments and nodes. Magnetometry and Mossbauer 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 the ferromagnetic phase is validated by the density functional theory calculations showing that local tetragonal distortion induced by surface stress favors ferromagnetic ordering. Our study provides a means for reaching conventionally inaccessible magnetic states, resulting in a complete on/off ferromagnetic-paramagnetic switching over a broad temperature range. This article is protected by copyright. All rights reserved.