Strain-induced fcc Fe nanocrystals confined in Al2O3 matrix

It is well known that the face-centered cubic (fcc) Fe is thermodynamically unstable at ambient conditions. In this paper, we theoretically and experimentally demonstrate that thermodynamically stable fcc Fe nanocrystals can be induced by external strain at room temperature. Fe nanocrystals confined in non-magnetic Al2O3 matrix are fabricated using pulsed laser deposition method and rapid thermal annealing technique. During the growth process, the confined Fe nanocrystals experience net deviatoric strain from the Al2O3 matrix, which can modify the microstructures of the confined Fe nanocrystals and lead to the formation of thermodynamically stable fcc Fe nanocrystals (space group Fm-3m) at room temperature. First-principles calculations also demonstrate that the strained Fe nanostructure with fcc phase is more thermodynamically stable. A typical behavior of weakly interacting Fe nanocrystals is observed, characterized by a superparamagnetic regime and a blocking of particle moments centered at T-B (similar to 9 K). (C) 2017 Elsevier B.V. All rights reserved.