Spin-singlet ground state of the coupled Jeff = 12 alternating chain system Sr2Co(SeO3)3

Abstract

We report a detailed study of the structural, magnetic, thermodynamic, and electronic properties of a coupled ${J}_{\mathrm{eff}}$ = $\frac{1}{2}$ alternating chain ${\mathrm{Sr}}_{2}\mathrm{Co}{({\mathrm{SeO}}_{3})}_{3}$ compound using magnetic susceptibility $\ensuremath{\chi}(T)$, magnetic specific heat ${C}_{\mathrm{m}}(T)$, magnetization, and neutron diffraction measurements along with first-principles calculations. The first-principles calculations based on the density functional theory suggest that ${\mathrm{Sr}}_{2}\mathrm{Co}{({\mathrm{SeO}}_{3})}_{3}$ forms a quasi-one-dimensional chain with bond alternation and interchain interactions. $\ensuremath{\chi}(T), {C}_{\mathrm{m}}(T),$ and neutron powder diffraction measurements confirm that no long-range magnetic ordering occurs down to 100 mK. Instead, a maximum in $\ensuremath{\chi}(T)$ and ${C}_{\mathrm{m}}(T)$ and an exponential drop of $\ensuremath{\chi}(T)$ and ${C}_{p}(T)$ as $T\ensuremath{\rightarrow}0$ K point to a spin-singlet ground state. The analysis of $\ensuremath{\chi}(T)$ and ${C}_{\mathrm{m}}(T)$ based on a ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ alternating Heisenberg model shows the bond alternation $\ensuremath{\alpha}={J}_{2}/{J}_{1}\ensuremath{\approx}0.7$ and a spin gap of $\mathrm{\ensuremath{\Delta}}\ensuremath{\approx}3$ K. Our work demonstrates that ${\mathrm{Sr}}_{2}\mathrm{Co}{({\mathrm{SeO}}_{3})}_{3}$ is a coupled alternating chain system based on spin-orbit entangled ${J}_{\mathrm{eff}}$ = $\frac{1}{2}$.