Gapped Spin Excitation in Magnetic Ordered State on Yb-Based Zigzag Chain Compound YbAgSe2

TL;DR

This study investigates the magnetic excitation properties of YbAgSe2 using 77Se-NMR, revealing a gapped excitation in its ordered state, contrasting with the gapless behavior observed in related compounds.

Contribution

The paper provides the first NMR analysis of YbAgSe2, demonstrating the presence of a magnetic excitation gap in its ordered state, differing from similar Yb-based zigzag chain compounds.

Findings

YbAgSe2 exhibits a magnetic excitation gap in the ordered state.

Contrasts gapless excitations in YbCuS2 with gapped behavior in YbAgSe2.

NMR results suggest suppression of gapless excitations under magnetic fields.

Abstract

We report the 77Se-nuclear magnetic resonance (NMR) results of trivalent Yb zigzag chain compound YbAgSe2, which is a sister compound of YbCuS2. The 77Se-NMR spectrum was reproduced by considering two different Se sites with negative Knight shifts and three-axis anisotropy. Above the Neel temperature TN, the Knight shift is proportional to the bulk magnetic susceptibility. Below TN, the extremely broad signal with weak intensity and the relatively sharp signal coexist, suggesting that one is strongly influenced by internal magnetic fields and the other remains relatively unaffected by these fields in the magnetic ordered state. The nuclear spin-lattice relaxation rate 1/T1 remains almost constant above TN and abruptly decreases below TN. In contrast to YbCuS2, a T-linear behavior of 1/T1 at low temperatures was not observed at least down to 1.0 K in YbAgSe2. Our results indicate that the gapless excitation is unique to YbCuS2, or is immediately suppressed in the magnetic fields.