Single crystal synthesis and nuclear magnetic resonance study of R3Co4Sn13 (R= La Ce Pr Yb) intermetallics

  • 劉 奐甫

Student thesis: Doctoral Thesis

Abstract

Ternary stannides with the cage-filled structure have been widely studied theoretically and experimentally due to the existence of interesting electronic and magnetic properties such as Heavy fermions superconductivity mixed-valence behavior complicated magnetism as well as three-dimensional charge-density-wave (CDW) instability In this thesis we report single crystal growth and a systematic study of ternary stannides R3Co4Sn13 (R = La Ce Pr Yb) including the specific heat magnetic susceptibility as well as 59Co and 119Sn nuclear magnetic resonance (NMR) measurements Each sample had been grown successfully by the Sn self-flux method Distinctive phenomena associated with the structural phase transition have been identified for La3Co4Sn13 Ce3Co4Sn13 and Pr3Co4Sn13 at T* ~ 152 K ~155 K and ~ 138 K respectively For those materials relative weak 59Co quadrupole splittings are consistently found below T* implying that the electrical field gradient (EFG) sensed by the Co site decreases undergoing this phase transition Such an observation could be attributed to the local distortion of the Sn(2) atom from its initial position below T* which consequently leads to significant modification of the electronic structures around the Fermi surfaces We also obtained a resolved 119Sn NMR spectrum on each compound However only 119Sn NMR line shape of Sn(2) for Ce3Co4Sn13 becomes broaden obviously and the peak feature smears below T* In addition its 119Sn NMR Knight shift versus magnetic susceptibility indicates an enhancement on the hyperfine coupling constant on Sn(2) across the phase transition Furthermore the evolution of 119Sn NMR line shape at various temperatures for La3Co4Sn13 and Pr3Co4Sn13 reveals a rather slightly modulation sensed by Sn(2) site for both compounds when crossing the transition consistent with each 119Sn NMR line shapes and Knight shift analyses For Yb3Co4Sn13 however the specific heat and NMR results show the absence of the structural-related phase transition The 59Co NMR Knight shift and spin-lattice relaxation rate 1/T1 clearly indicate that Yb3Co4Sn13 is a Pauli-type paramagnet Based on the Korringa relation (constant T1T) we thus estimated Co 3d Fermi-level density of states Nd(EF) ~ 3 95 states/eV f u for this compound
Date of Award2016 Jul 28
Original languageEnglish
SupervisorChin-Shan Lue (Supervisor)

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