Superconducting and Ferromagnetic Phases Induced by Lattice Distortions in Stoichiometric SrFe₂As₂ Single Crystals

Single crystals of SrFe₂As₂ grown using a self-flux solution method were characterized via x-ray, transport, and magnetization studies, revealing a superconducting phase below T_c=21  K characterized by a full electrical resistivity transition and partial diamagnetic screening. The reversible destruction and reinstatement of this phase by heat treatment and mechanical deformation studies, along with single-crystal x-ray diffraction measurements, indicate that internal crystallographic strain originating from c-axis-oriented planar defects plays a central role in promoting the appearance of superconductivity under ambient-pressure conditions in ∼90% of as-grown crystals. The appearance of a ferromagnetic moment with magnitude proportional to the tunable superconducting volume fraction suggests that these phenomena are both stabilized by lattice distortion.