|Budget Amount *help
¥2,900,000 (Direct Cost : ¥2,900,000)
Fiscal Year 1999 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1998 : ¥2,100,000 (Direct Cost : ¥2,100,000)
Coexistence of superconductivity and magnetic order has been reported for the cubic Heusler alloys ErPdィイD22ィエD2Sn (Tc = 1.17 K, TィイD2NィエD2 = 1.0 K) and YbPdィイD22ィエD2Sn (Tc = 2.3 K, TィイD2NィエD2 = 0.22 K). We have prepared a polycrystalline YbPdィイD22ィエD2Sn sample, investigated the superconducting transition by electrical resistivity, magnetic ac susceptibility and specific heat experiments and performed low temperature neutron diffraction experiments down to 30 mK to determine the kind of magnetic structure that coexists with superconductivity. The results showed that the magnetic structures that coexist with superconductivity are different for ErPdィイD22ィエD2Sn (FCC-type II antiferromagnet, k=[1/2, 1/2, 1/2] with an additional incommensurate component) and for YbPdィイD22ィエD2Sn (FCC type I antiferromagnet, k=[0, 0, 1], with no incommensurate component).
For the high-temperature superconductors RィイD22ィエD2BaィイD24ィエD2CuィイD27ィエD2OィイD215-δィエD2(R=Dy,Er) we have used the sol gel technique to prepar
e large amounts (over 3 cmィイD13ィエD1) of single phase samples. By systematic measurements of the low temperature specific heat we have studied the long- and short-range magnetic rare-earth interactions which coexist with superconductivity as a function of the rare-earth element (R) and of the oxygen content (δ). According to our specific heat results, changing the oxygen concentration in Er247 samples from a high or a low value to an intermediate value causes a larger in-plane anisotropy and tends to lower dimensionality and correlation range of the magnetic interactions of the ErィイD13+ィエD1 ions. Such an effect is not observed for the Dy247 samples, where the specific heat anomaly at TィイD2NィエD2 = 1.0 K is found to be almost independent of the oxygen concentration except for a small broadening for the sample DyィイD22ィエD2BaィイD24ィエD2CuィイD27ィエD2OィイD214.45ィエD2 with intermediate oxygen content, where electronic disorder in the CuOィイD22ィエD2-planes causes some disorder in the exchange interactions. Less