P-NMR study of hyperfine interactions and magnetic fluctuations in the neptunium-based filled skutterudite NpFeP

Tokunaga, Yo  ; Kambe, Shinsaku  ; Sakai, Hironori   ; Chudo, Hiroyuki ; Matsuda, Tatsuma; Haga, Yoshinori   ; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; Onuki, Yoshichika

P-NMR measurements have been performed on a single crystal of the neptunium-based filled skutterudite NpFeP. We have observed transferred hyperfine interactions at the P sites, which lead to an estimate of the local spin density in the P 3 orbitals. It is shown that a fraction of the Np 5 spin moments is transferred mostly into the P 3 orbitals extending toward the inside of a P-cage. The weak hybridization between Np 5 and P 3 orbitals suggests a localized character for Np 5 electrons. We have also measured the field and temperature dependences of the nuclear spin-lattice relaxation rate (). The data reveal that the low-energy spin fluctuations of Np 5 spin moments are strongly suppressed by applied fields over a relatively wide temperature range. The present NMR results demonstrate that the negative magnetoresistance comes from a reduction of the magnetic scattering from Np 5 spin moments by an applied field.