Interplay of nuclear magnetism and superconductivity

The ratio of nuclear saturation magnetization and superconducting critical field, mu(0)M(sat)/B-S0* = epsilon, classifies the strength of mutual influence of nuclear magnetism and superconductivity. In order to investigate the interplay of both phenomena for the three distinct cases epsilon much less than 1, epsilon approximate to 1, and epsilon much greater than 1 we have measured the ac susceptibility of Al, of the intermetallic compound AuIn2, and of the metal hydride TiH2.07 at ultralow temperatures, 17 mu K less than or equal to T less than or equal to 1 K, as function of static field 0 less than or equal to B less than or equal to 15 mT. For Al, the interplay enables an absolute measurement of the nuclear magnetization. For AuIn2, we get a steel, decrease of Bs(T) and a broadening of the superconducting transition in its nuclear ferromagnetic phase. Surprisingly, the nuclear ferromagnetic state coexists with type-I superconductivity in AuIn2. The metal hydride TiH2.07, which is under present investigation, is a good candidate to show reentrant superconductivity.