$^1$H-NMR Study of the Random Bond Effect in the Quantum Spin System (CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$

TL;DR

This study uses $^1$H-NMR to investigate the microscopic effects of bond randomness in a gapped quantum spin system, revealing coexistence of gapless and gapped magnetic states.

Contribution

It provides the first microscopic evidence of bond randomness effects in a gapped quantum spin system using NMR relaxation measurements.

Findings

Detection of both fast and slow relaxation components indicating coexistence of magnetic states.

Microscopic evidence supporting previous macroscopic measurements of bond randomness effects.

Insight into the local magnetic environment in a bond-disordered gapped system.

Abstract

Spin-lattice relaxation rate $T_1^{-1}$ of $^1$H-NMR has been measured in (CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$ with $x=0.88$, which has been reported to be gapped system with singlet ground state from the previous macroscopic magnetization and specific heat measurements, in order to investigate the bond randomness effect microscopically in the gapped composite Haldane system (CH$_3$)$_2$CHNH$_3$CuCl$_3$. It was found that the spin-lattice relaxation rate $T_1^{-1}$ in the present system includes both fast and slow relaxation parts indicative of the gapless magnetic ground state and the gapped singlet ground state, respectively. We discuss the obtained results with the previous macroscopic magnetization and specific heat measurements together with the microscopic $\mu$SR experiments.