Emergence of unconventional spin glass-like state in κ - (ET)2Cu[N(CN)2]Cl by introducing weak randomness

Abstract

Recently, Urai et al. [Phys. Rev. Lett. 124, 117204 (2020)] reported that an antiferromagnetic long-range-ordered state in $\ensuremath{\kappa}$-${(\mathrm{ET})}_{2}\mathrm{Cu}\mathrm{[N}{(\mathrm{CN})}_{2}\mathrm{]Cl}$ changes into a quantum spin liquid via an unconventional spin glass-like state as randomness is introduced by x-ray irradiation. Here, we focused on the spin glass-like state and conducted a detailed investigation into it using $^{13}\mathrm{C}$-NMR measurements on 150-h x-ray-irradiated $\ensuremath{\kappa}$-$({\mathrm{ET})}_{2}\mathrm{Cu}\mathrm{[N(}{\mathrm{CN})}_{2}\mathrm{]Cl}$. We found that the spin glass-like state is composed of two components: the major component inherits the spin structure of nonirradiated $\ensuremath{\kappa}$-$({\mathrm{ET})}_{2}\mathrm{Cu}\mathrm{[N(}{\mathrm{CN})}_{2}\mathrm{]Cl}$, whereas the minor component differs from that of nonirradiated $\ensuremath{\kappa}$-${(\mathrm{ET})}_{2}\mathrm{Cu}\mathrm{[N(}{\mathrm{CN})}_{2}\mathrm{]Cl}$. We also found that in the spin glass-like state, spin moments fluctuate very slowly around stable directions even at low temperatures, which is very likely related to the Griffiths physics.