Visualization of structural domains in a single crystal of iron pnictide EuFe₂As₂

Abstract

It is known that during the synthesis of superconducting EuRbFe4As4 single crystals, inclusions of its parent EuFe2As2 phase are encountered. The kinetics of the formation of the orthorhombic phase in EuRbFe4As4 crystals containing a large fraction of the EuFe2As2 phase has been studied using polarization optical microscopy. It is shown that the orthorhombic phase grows into the tetragonal one in stripes with the same crystallographic orientation, forming macro-domains. Then these domains abruptly penetrate parallel stripes of the orthorhombic phase of the second orientation, and a twin system of orthorhombic domains is formed. The process is accompanied by the appearance of macrostresses: stretching and compression waves with a characteristic period of 100–300 μm along and across the twin system, leading to spatial modulation of magnetic permeability. It has been found that even weak magnetic fields (up to 100 Oe) significantly affect the spatial distribution of the twin structure and have an effect similar to external stresses.