Superconductivity and Magnetism in Selected Filled Skutterudites and Heavy Fermion Systems PDF Download

Author: Ram Bahadur Adhikari
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Languages : en
Pages : 0

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Book Description
Strongly correlated electron systems constitute a rich reservoir for interesting physical phenomena. The competition and interplay between the localized magnetic moments in partially filled d or f electron systems and the itinerant conduction electrons states lead to novel phenomena such as complex magnetic properties, unconventional superconductivity, non-Fermi-liquid behavior, and the coexistence of superconductivity and magnetism. Such intriguing physical phenomena can be achieved by tuning the system with a control parameter, such as chemical composition, applied pressure, and magnetic field. It is interesting to study the chemical substitution effects on the correlated f electron system along with magnetic field to explore their complex phase diagram. This dissertation work focuses on experimental studies of the Ce and Eu substituted filled skutterudite system PrPt4Ge12 over a wide range of doping, magnetic field, and temperature using heat capacity measurements. The first study will focus on the specific heat and electrical resistivity measurements performed on the Pr[subscript 1-x]Ce[subscript x]Pt4Ge12 crystals. We have found that Ce monotonically suppresses the superconducting transition temperature T[subscript c] and a small Ce concentration of x = 0.14 brings the T[subscript c] to as low as 0.6 K. We further have demonstrate that small Ce substitution does not affect the multiband nature of superconductivity seen previously in the parent compound PrPt4Ge12. On the other hand, our data provide evidence that one of the two gaps is nodal in the parent compound and that Ce substitution gradually suppresses the value of the nodal gap. To understand the possible interplay between superconductivity and magnetism, we study the same parent system PrPt4Ge12, this time substituting Pr with europium. The compound so formed is Pr[subscript 1-x]Eu[subscript x]Pt4Ge12 whose end members are superconductor (x = 0) and antiferromagnetic (x = 1) at lower temperatures, so that there is the possibility of interaction between superconductivity and magnetism in the intermediate doping range. The increase of Eu concentration leads to a suppression of the superconducting transition temperature as in the case of cerium substitution. There is a low temperature heat capacity anomaly present over the whole doping range. Our analysis of the heat capacity data shows that in alloys with x = 0.5 the Schottky peaks in the heat capacity in the superconducting state appear to be due to Zeeman splitting by an internal magnetic field. Our theoretical analysis suggests that this internal magnetic field is a result of short-range antiferromagnetic correlations between the europium ions. We further investigated the effect of Eu substitution on the Pr site through heat capacity measurements on the same system in an applied magnetic field. The low temperature heat capacity peaks seen in the samples with x