Single crystal growth and NMR studies of R3Co4Sn13 (R = La, Ce, Pr, Yb) compounds
Huan-Fu Liu(劉奐甫)1*, C. N. Kuo(郭家農)1,2, C. S. Lue(呂欽山)1,2, Y. K. Kuo(郭永綱)3
1Department of Physics, National Cheng Kung University, Tainan, Taiwan
2Taiwan Consortium of Emergent Crystalline Materials, Ministry of Science and Technology, Taipei, Taiwan
3Department of Physics, National Dong Hwa University, Hualien, Taiwan
* presenting author:Huan-Fu Liu,
We report single crystal growth and a systematic study of ternary stannides R3Co4Sn13 (R = La, Ce, Pr, Yb) including the specific heat, 59Co and 119Sn nuclear magnetic resonance (NMR) measurements. Each sample has 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* ~ 160 K, ~155 K and ~ 130 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 compounds. 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.

Keywords: Electron density of states and band structure of crystalline solids, Intermetallic compounds, Nuclear magnetic resonance and relaxation