Inhaltszusammenfassung

The phase boundaries between superconductivity and various types of magnetism in the pseudoternary system I-Io(Rhl_xRux)4B4 were examined by lowtemperature measurements of the specific heat c(T), dc magnetization M(H), superconducting upper critical field Hcz(T), and ac susceptibility Xac(T). For Ru concentrations x<~ 0.37 superconductivity coexists with antiferromagnetic order below about I K, as shown by characteristic minima in the Hcz(T) curves and an extrapolation of M(H) data. Add...The phase boundaries between superconductivity and various types of magnetism in the pseudoternary system I-Io(Rhl_xRux)4B4 were examined by lowtemperature measurements of the specific heat c(T), dc magnetization M(H), superconducting upper critical field Hcz(T), and ac susceptibility Xac(T). For Ru concentrations x<~ 0.37 superconductivity coexists with antiferromagnetic order below about I K, as shown by characteristic minima in the Hcz(T) curves and an extrapolation of M(H) data. Additionally, the H~z(T) measurements exhibit an unusual hysteresis between data taken in increasing and decreasing fields below 0.6 K. As a starting point for a theoretical explanation of this feature, a mean-field model is proposed with antiferromagnetic as well as ferromagnetic interactions, which are tentatively identified as the RKKY and dipole-dipole interactions. The existence of two competing interactions is supported by the observation of a time-dependence of the Xac signal at 50 mK for 0.40 ~ x-< O. 70, leading to a pronounced hysteresis in Xac (T), which reflects a relaxation of the magnetic structure with time constants of several hours. For x -> 0.80 the Xa,(T) and M(H) data indicate ferromagnetic ordering with Tm increasing with x. However, an irregular temperature dependence of the Arrott plots for x = 1.0 and unusual features of the magnetic c(T) anomalies for x = 0.95 and 1.0 exclude simple mean-field ferromagnetism. A discussion of the experimental results based on an x-dependent variation of the electronic density of states at the Fermi level is presented.» weiterlesen» einklappen

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Klassifikation

DFG Fachgebiet:
Physik der kondensierten Materie

DDC Sachgruppe:
Physik