Synthesis and properties of 12442-family superconductor1)
I. V. Zhuvagin, V. A. Vlasenko, A. S. Usoltsev, A. A. Gippius, K. S. Pervakov, A. R. Prishchepa, V. A. Prudkoglyad, S. Yu. Gavrilkin, A. D. Denishchenko, A. V. Sadakov2)
Lebedev Physical Institute, Russian Academy of Sciences, 119991 Moscow, Russia
Abstract
We report a synthesis of two members of recently discovered high-temperature
superconductors of 12442 family, with formula MCa2Fe4As4F2 (M = Rb, K)
and transition temperatures of 32.7 and 34.6 K, respectively. Quality of the samples was assessed
using X-ray powder diffraction, superconducting transitions were identified through transport and
magnetic experiments. The temperature dependence of the upper critical field and vortex activation
energy was investigated under magnetic fields up to 19 T. Two distinct thermally activated flux flow
regimes were observed in both systems. Field dependences of activation energy U0(H) indicate a
change in the properties of vortex matter in these regimes and distinctly different dissipation
mechanisms, reminiscent of cuprate HTSC.