Anomalous Enhancement of Nuclear Spin Relaxation Rates of 109Ag and 115In at Low Temperatures in Cubic Γ3 Ground-State System PrAg2In –First Observation of Octupole Fluctuations of f-Electrons–

Abstract

Microscopic properties have been investigated on a cubic nonmagnetic non-Kramers Γ 3 doublet ground-state (GS) system PrAg 2 In by complementarily utilizing 115 In ( I =9/2) and 109 Ag ( I =1/2) NMR with particular emphasis on the low-frequency (low-ω) dipole and multipole (octupole and/or quadrupole) fluctuations of f -electrons as probed by the nuclear spin relaxation rates 1/ 115 T 1 and 1/ 109 T 1 . We show that 1/ 115 T 1 and 1/ 109 T 1 are anomalously enhanced respectively below \({\cong}50\) K and \({\cong}100\) K over those expected for the low-ω dipole fluctuations of the excited magnetic Γ 4 and Γ 5 states in a simple crystalline-electric-field model for a Γ 3 GS system. By comparing 1/( 115 T 1 T ) and 1/( 109 T 1 T ) and also by considering an invariant form of the hyperfine and/or quadrupole couplings of Γ 3 octupole and/or quadrupole moments with Ag/In nuclear dipole and/or quadrupole moments, we show that Γ 3 octupole fluctuations dominate 1/ 109 T 1 and quadrupole ones can possibly contribute to 1/ 115 T 1 at low T .