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 (∼9 K). - Highlights: • Fe nanocrystals experience net deviatoric strain from Al₂O₃ matrix during growth. • The strain can change the microstructure of the confined Fe nanocrystals. • The thermodynamically stable fcc Fe nanocrystals can be induced by external strain.