Visualization of the magnetic flux structure in phosphorus-doped EuFe 2 As 2 single crystals

Magnetic flux structure on the surface of EuFe 2 (As 1- x P x ) 2 single crystals with nearly optimal phosphorus doping levels x = 0.20 and x = 0.21 is studied by low-temperature magnetic force microscopy and decoration with ferromagnetic nanoparticles. The studies are performed in a broad temperature range. It is shown that the single crystal with x = 0.21 in the temperature range between the critical temperatures T SC = 22 K and T C = (18 ± 0.3) K of the superconducting and ferromagnetic phase transitions, respectively, has the vortex structure of a frozen magnetic flux, typical for type-II superconductors. The magnetic domain structure is observed in the superconducting state below T C . The nature of this structure is discussed.