No abstract available

[en] The appearance of impurity phases belonging to the quaternary oxide system SrO-GdO_1.5-CuO-RuO₂ in Ru-1212 samples is difficult to avoid. While the formation of the ferromagnetic compound SrRuO₃ may be suppressed by a precursor route involving Sr₂GdRuO₆, this latter compound shows magnetization anomalies below 30 K. We present evidence that magnetization anomalies observed for some Ru-1212 samples in this temperature range are not due to trace amounts of Sr₂GdRuO₆. Rather, the effect appears to be related to the establishment of inter-granular superconductivity and to the vortex dynamics in Ru-1212

No abstract available

[en] We have demagnetized 8.3mmol AuIn₂ and measured its heat capacity C at 2mT≤B≤115mT and 40μK≤T≤1mK. We get C∝B²/T² with B²=B_ext²+b_int² at ''high'' temperatures. At the lowest temperatures C is strongly enhanced above this Schottky behaviour. In fields B≥47mT we observe a maximum in C. In smaller fields the maxima are below the temperatures accessible to us. The 16Hz-susceptibility was measured in fields B_ext≤20mT. In the temperature range of enhanced C-values we also get enhanced χ-values. The χ-data again indicate a zero-field T_c=40μK and a internal field b_int (B_ext→0)=8mT. (orig.)

No abstract available

[en] We report on a new type of magnetic superconductor investigated by susceptibility measurements of AuIn₂ at 25μK≤T≤207 mK and 0.01mT≤B≤2.00mT. These experiments have been performed to study the interplay between nuclear ferromagnetism and type-I superconductivity. We observe a decrease of the critical field B_s and a broadening of the superconducting transition of the type-I superconductor AuIn₂ [T _s|_B=0=207mK] caused by the coexisting nuclear ferromagnetic state starting at T_c=37μK. This is the first study on the interplay of nuclear magnetism and superconductivity. copyright 1997 The American Physical Society

[en] The interplay of magnetism and superconductivity has intrigued physicists since the late fifties. The advance of ultralow temperature technology has recently allowed to extend these studies to nuclear magnetism. We have measured the influence of nuclear magnetism on superconducting critical fields B_s,c of Sn, AuIn₂, Al, and AuAl₂, at ultralow temperatures, 17 μK ≤T ≤ 1 K. The materials have been chosen in respect to their very different hyperfine coupling expressed by the Korringa constants K (Sn, AuIn₂, Al, AuAl₂) = (0.05, 0.11, 1.8, 18) Ksec. Both, for the strongly and for the weakly coupled nuclear paramagnets, Sn, AuIn₂, and Al a reduction of B_s,c, is observed being proportional to the nuclear magnetization. However, for AuAl₂ with its extremely weak hyperfine coupling between Al nuclear moments and conduction electrons, almost no influence of nuclear magnetization on B_s,c = 1.2 mT is observed within our experimental resolution of 0. 1 μT. In addition, we had observed formerly a spontaneous nuclear ferromagnetic transition of the strongly interacting In nuclei in AuIn₂, at T_m,c= 37 μK. Besides the above mentioned reduction of B_s,c in the nuclear paramagnetic state, we observe a sudden reduction of B_s,c by 40% below T_m,c leading then to the first observation of coexistence of (nuclear) ferromagnetism and superconductivity. (author)

[en] Nuclear magnetic resonance, ac susceptibility and nuclear heat capacity of two Pt samples with different concentrations of magnetic impurities (41 ppm and 11 ppm), most likely Fe, have been studied in fields of (0 ± 0.05) mT ≤ B ≤ 248 mT and at temperatures of 0.3 μK ≤ T ≤ 100 mK. No indication for a nuclear magnetic ordering to T_e = 2 μK (NMR) in 2.5 mT and to a nuclear temperature T_n = 0.3 μK (ac susceptibility) in (0 ± 0.05) mT could be detected, and a maximum for the Weiss constant of 0.3 μK can be estimated. The nuclear heat capacity data show enhanced values which scale with the impurity concentration. This latter data can be described with a spatially varying field caused by the magnetic impurities

[en] A substantial decrease of the critical field of superconductivity (T_s = 207 mK for B = 0) was observed for AuIn₂ in its ordered nuclear ferromagnetic phase. When decreasing the temperature from T = 42 μK (susceptibility maximum) to 25 μK, the critical field is reduced from B_s (T > T_C) = 1.45 mT in the nuclear paramagnetic phase to B_s (T < T_C) = 0.87 mT in the nuclear ferromagnetic phase at T = 25 μK. In addition, a broadening of the superconducting transition in the nuclear ordered phase was observed

[en] The 16 Hz proton nuclear susceptibility of high purity TiH_1.98 and TiH_1.76 was measured at temperatures of 80 μK ≤ T ≤ 120 mK and in fields of 0.01 mT ≤ B ≤ 2 mT. The data show Curie-Weiss behaviour (with a Weiss constant θ = (-4.0 ± 1.0) mK at T ≥ 5 mK for TiH1_.98) followed by a maximum at (1.0 ± 0.3) mK and (3.0 ± 0.3) mK for TiH_1.98 and TiH_1.76, respectively. This could be interpreted as an antiferromagnetic ordering transition of the protons in the metal hydride