Unusual Suppression of Low Energy Spin Excitations near Fermi Level in AFe_4Sb_<12> (A=Ca, Sr, and Ba) Probed by Sb-NQR(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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Sb nuclear quadrupole resonances (NQR) have been performed on the alkaline-earth filled skutterudite AFe_4Sb_<12> (A=Ca, Sr, and Ba) being close to ferromagnetic instabiity. No hyperfine splitting in NQR spectrum even at the lowest temperature (1.5K) confirms an absence of uniform ferromagnetic order in these compounds. Above about T*〜70K, the nuclear spin-lattice relaxation rate divided by temperature, 1/T_1T, follows an empirical relationship 1/T_1T=a+b_<χ_<spin>> with respect to the Curie Weiss (CW) like T-dependence of the static spin susceptibility _<χ_<spin>>. The correlation between 1/T_1T and _<χ_<spin>> is consistent with the self-consistent renormalization (SCR) theory for the three-dimensional (3D) nearly ferromagnet despite the relatively large contribution of the first term not correlating to _<χ_<spin>>. However, below about T*, 1/T_1T exhibits a gap-like suppression with a gap magnitude of about 65K. This unusual suppression of the low energy spin excitations is contrasting to the case in LaFe_4Sb_<12>, and a characteristic feature in the filled skutterudites with divalent filler ion. The pseudo-gap structure near the Fermi level is proposed for the hybridized Fe3d-Sb5p band (mainly partial p state) for the unusual suppression.
社団法人日本物理学会の論文
2007-08-15