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In the two-phase crystal EuRbFe4As4/EuFe2As2 (1144/122), a linear ordering of Abrikosov vortices, uncharacteristic for superconducting pnictides, has been found using the method of decorating with magnetic nanoparticles. The observed chains of vortices directed along crystallographic 〈110〉 axes of the orthorhombic EuFe2As2 phase are explained by pinning of vortices in the superconducting phase 1144 on linear defects associated with the twin boundaries of the non-superconducting 122 phase. [ABSTRACT FROM AUTHOR]

In the two-phase crystal EuRbFe4As4/EuFe2As2 (1144/122), a linear ordering of Abrikosov vortices, uncharacteristic for superconducting pnictides, has been found using the method of decorating with magnetic nanoparticles. The observed chains of vortices directed along crystallographic 〈110〉 axes of the orthorhombic EuFe2As2 phase are explained by pinning of vortices in the superconducting phase 1144 on linear defects associated with the twin boundaries of the non-superconducting 122 phase. [ABSTRACT FROM AUTHOR]

It is known that, during the synthesis of superconducting EuRbFe4As4 single crystals, inclusions of its parent phase EuFe2As2 are encountered. The kinetics of the formation of the orthorhombic phase in EuRbFe4As4 crystals containing a large fraction of the EuFe2As2 phase is studied using polarization optical microscopy. It is shown that the orthorhombic phase grows into the tetragonal one in the form of stripes that form macrodomains with one of the possible crystallographic orientations. Then these domains are abruptly penetrated by parallel stripes of the orthorhombic phase having the second orientation, as a result of which 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, which lead to spatial modulation of the magnetic permeability. It is found that even weak magnetic fields (up to 100 Oe) significantly affect the spatial distribution of the twin structure producing an effect similar to external stresses. [ABSTRACT FROM AUTHOR]