Coexistence of antiferromagnetism with superconductivity in CePtIn; Microscopic phase diagram determined by In NMR and NQR

CePtInにおける超伝導と反強磁性の共存; In核-核磁気共鳴(NMR)法と核四重極共鳴(NQR)法によって決めた微視的相図

酒井 宏典   ; 徳永 陽  ; 神戸 振作  ; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

常圧で重い電子系反強磁性体であるCePtIn (=5.2K)のIn核-核磁気共鳴(NMR)及び核四重極共鳴(NQR)測定を圧力下において行った。Ce 電子の反強磁性状態は約2.4GPaのところで、局在的から遍歴的な性質を示すようになり、超伝導が観測されるようになる。さらに加圧すると、3.4GPaのところで、反強磁性秩序は完全に抑制され、NMR緩和率は超伝導転移温度において、通常よりも鋭く、一次転移的に減少を示した。

Single crystals of the heavy-fermion antiferromagnet CePtIn with a Nel temperature () of 5.2 K at ambient pressure have been investigated by zero-field In-nuclear magnetic/quadrupole resonance (NMR/NQR) measurements as a function of applied pressure. Within the antiferromagnetic state the character of Ce's electron appears to change from localized to itinerant-like at GPa, approximately the pressure where superconductivity first emerges. With increased pressure, the superconducting transition reaches a maximum just at or slighty before antiferromagnetic order disappears, and not at the pressure GPa where the steeply decreasing Nel boundary extrapolates to zero temperature. For , the spin relaxation rate drops sharply by more than two orders of magnitude at , suggestive of a first order transition.