Effect of impurities on superconductors with helical ordering of localized spins

Cooper pairing of electrons in a crystal with regularly distributed localized spins is considered. The case is studied in which exchange interaction between the electrons and localized spins leads to helical magnetic ordering of the localized spins in the superconducting state, whereas in the absence of superconductivity ferromagnetic order would occur. It is shown that scattering of conducting electrons by nonmagnetic impurities narrows the region of existence of the superconducting phase with spin ordering (HS phase). The narrowing, however, is not very pronounced even in dirty crystals. Thus the requirement of the purity of the crystals in which the HS phase may be observed is not very rigid