Abstract
121 Sb Knight shift K measurement has been carried out by applying a perturbing field to the nuclear quadrupole resonance (NQR) spectrum in alkaline-earth filled skutterudites A Fe 4 Sb 12 ( A = Ca and Sr), which are close to ferromagnetic instability. The hyperfine coupling constant was determined for the first time as -14.9 kOe/µ B f.u. from the K –χ plot. This relatively large value suggests a strong Fe–Sb covalent bonding. The intrinsic spin susceptibility χ spin derived from K markedly decreases at low temperatures after Curie–Weiss-like increase at high temperatures, which seems to be responsible for the absence of ferromagnetic order. Using the T -dependence of χ spin , the unusual gap-like suppression of nuclear spin–lattice relaxation rate divided by temperature 1/ T 1 T in our previous report is reasonably explained by assuming the spin dependent-term to be proportional to χ spin and the gap-like suppression of the spin-independent term.
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