We have synthesized two iron fluo-arsenides ACa2Fe4As4Fz with A = Rb and Cs, analogous to the newly discovered superconductor KCazFe4As4F2. The quinary inor- ganic compounds crystallize in a body-centered tetragonal lattice with space group I4/mmm, which contain double Fe2As2 layers that are separated by insulating Ca2F2 layers. The electrical and magnetic measurements on the polycrys- talline samples demonstrate that the new materials undergo superconducting transitions at Tc = 30.5 and 28.2 K, respec- tively, without extrinsic doping. The correlations between Tc and structural parameters are discussed.
Superconductivity （SC） and ferromagnetism （FM） are in general antagonistic, which makes their coexistence very rare. Following our recent discovery of robust coexistence of SC and FM in RbEuFe4As4 （Liu et al. in Phys Rev B 93：214503, 2016）, here we report another example of such a coexistence in its sister com- pound CsEuFe4As4, synthesized for the first time. The new material exhibits bulk SC at 35.2 K and Eu2＋-spin ferro- magnetic ordering at 15.5 K, demonstrating that it is a new robust ferromagnetic superconductor.
