Interplay of Nuclear Magnetism and Superconductivity

Abstract

The ratio of nuclear saturation magnetization and superconducting critical field, μ ₀ M _sat / B _S0*≡∈, 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 ∈ ≪ 1, ∈ ≍ 1, and ∈ ≫ 1 we have measured the ac susceptibility of Al, of the intermetallic compound AuIn ₂ , and of the metal hydride TiH _2.07 at ultralow temperatures, 17 μK ≤ T ≤ 1 K, as function of static field 0 ≤ B ≤ 15 mT. For Al, the interplay enables an absolute measurement of the nuclear magnetization. For AuIn ₂ , we get a steep decrease of B _S (T) and a broadening of the superconducting transition in its nuclear ferromagnetic phase. Surprisingly, the nuclear ferromagnetic state coexists with type-I superconductivity in AuIn ₂. The metal hydride TiH _2.07 , which is under present investigation, is a good candidate to show reentrant superconductivity.