Inhaltszusammenfassung

The phase boundaries between the paramagnetic, superconducting, and ferromagnetically ordered states of the tetragonal pseudoternary system GdxY1-xRh4B4 have been determined by ac susceptibility measurements. Magnetization measurements, performed with cylindrical samples for 0?x?0.45 at temperatures above 1.5 K, show clearly that macroscopic electromagnetic effects are of minor importance in this system and indicate a transition from type-II/2 to type-II/1 or type-I superconductivity at tempe...The phase boundaries between the paramagnetic, superconducting, and ferromagnetically ordered states of the tetragonal pseudoternary system GdxY1-xRh4B4 have been determined by ac susceptibility measurements. Magnetization measurements, performed with cylindrical samples for 0?x?0.45 at temperatures above 1.5 K, show clearly that macroscopic electromagnetic effects are of minor importance in this system and indicate a transition from type-II/2 to type-II/1 or type-I superconductivity at temperatures close to Tc2. For the critical fields we obtain from the magnetization curves a sawtoothlike Hc1(T), scaling with Tc1(x), whereas Hc2(T) is bell shaped for x?0.1, with its maximum decreasing exponentially with x for x?0.30. From Arrott plots we find spontaneous magnetizations below Tm and Curie-Weiss laws for the normal-state susceptibility indicating ferromagnetic Curie temperatures ?c>0 for x>0.1. Analyzing the data we show that the strength of the exchange interaction between the conduction electrons and the Gd moments deduced from Tc1(x) is strong enough to mediate the indirect interaction between the Gd moments as found from ?c(x). From specific-heat measurements carried out for x=0.25 and 0.45 we obtain N*(EF)=0.57 states/(atom eV spin), in agreement with the nonmagnetic Y and Lu compounds. The details of the magnetic transitions appear to scale with the Gd concentration. » weiterlesen» einklappen

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Klassifikation

DFG Fachgebiet:
Physik der kondensierten Materie

DDC Sachgruppe:
Physik