Polarized Light Microscopy Study on the Reentrant Phase Transition in a (Ba1 – xKx)Fe2As2 Single Crystal with x = 0.24

Abstract

A sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba1 − xKx)Fe2As2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba1 − xKx)Fe2As2 (x = 0.24) single crystal below a temperature of simultaneous structural/magnetic transition TN ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT) to low temperature orthorhombic (LTO1) structure at TN ~ 80 K, LTO1 to low temperature tetragonal (LTT) structure at Tc ~ 25 K, and LTT to low temperature orthorhombic (LTO2) structure at T ~ 15 K.

Keywords

• reentrant phase transition
• polarized optical images
• structural domains