- Jiří Pospíšil: Field induced phenomena in UCo1-xRhxGe system
- 25. 10. 2017, 14:30
- lecture room F2, first floor Ke Karlovu 5
- more information
Abstract:
The close relation between ferromagnetism and superconductivity is reflected to the complex H-T-p phase diagrams of the ferromagnetic superconductors UCoGe and URhGe. Unique field-induced SC dome appears in URhGe[1] in the vicinity of critical magnetic field HR = 12 T applied along the orthorhombic b axis. Here, ferromagnetism is vanished by the first order transition projected to b-axis magnetization curve as a sharp jump. However, distinct discrepancy in relation between magnetic and superconducting features of UCoGe and URhGe was observed. The high magnetic field study of UCoGe detected some broad S-shape jump in the magnetization isotherm along the b-axis at significantly higher field Hm of almost 50 T[2], which clearly does not coincide with the area of the enhanced superconductivity in magnetic field ~15 T along the identical axis[3]. Another striking feature of the phase diagrams of both compounds is presence of the characteristic temperature Tmax. Tmax = 30 K is defined in UCoGe at top of a broad maximum detected in the temperature dependence of magnetic susceptibility along the b axis[2] in contrast to a sharp peak at Tmax = 9.5 K in URhGe[4]. Tmax fundamentally differentiates both compounds because Tmax >> TC in UCoGe while Tmax = TC in URhGe, respectively. UCo1-xRhxGe alloy system was already studied by polycrystals[5], however, the evolution of the key effects as the fine S-shape jump in magnetization and Tmax in the susceptibility remained hidden due to strong magneto-crystalline anistropy.
Our extensive single-crystal study of the UCo1-xRhxGe by heat capacity and convetional and pulsed field magnetization uncovered the evolution of magnetism throughout the given system. We could clearly distinguish two ferromagnetic regions. First, between UCoGe and UCo0.7Rh0.3Ge with decoupled TC < Tmax with low magnetic entropy and second, between UCo0.6Rh0.4Ge and URhGe with TC = Tmax characterized by high magnetic entropy. Character of both ferromagnetic regions will be discussed with potential consequences in the observed superconducting features of the parent compounds.
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