Role of crystal field ground state in the classical spin-liquid behavior of a quasi-one dimensional spin-chain system Sr3NiPtO6

Abstract

The spin-chain compound Sr3NiPtO6 is known to have a nonmagnetic ground state. We have investigated the nature of ground state of Sr3NiPtO6 using magnetic susceptibility $\ddot{I}‡(T)$, heat capacity $C_{\mathrm{p}}(T)$, muon spin relaxation ($\hat{I}¼$SR) and inelastic neutron scattering (INS) measurements. The $\ddot{I}‡(T)$ and $C_{\mathrm{p}}(T)$ do not exhibit any pronounced anomaly that can be associated with a phase transition to a magnetically ordered state. Our $\hat{I}¼$SR data confirm the absence of long-range magnetic ordering down to 0.04 K. Furthermore, the muon spin relaxation rate increases below 20 K and exhibits temperature independent behavior at low temperature, very similar to that observed in a quantum spin-liquid system. The INS data show a large excitation near 8~meV, and the analysis of the INS data reveals a singlet CEF ground state with a first excited CEF doublet state at $\hat{I}{”}_{\mathrm{CEF}}$ = 7.7 meV. The estimated CEF parameters reveal a strong planar anisotropy in the calculated $\ddot{I}‡(T)$, consistent with the reported behavior of the $\ddot{I}‡(T)$ of single crystal Sr3NiPtO6. We propose that the nonmagnetic singlet ground state and a large $\hat{I}{”}_{\mathrm{CEF}}$ (much larger than the exchange interaction ${\mathcal{J}}_{\mathrm{ex}}$) are responsible for the absence of long-range magnetic ordering and can mimic a classical spin-liquid behavior in this quasi-1D spin chain system Sr3NiPtO6. The classical spin-liquid ground state observed in Sr3NiPtO6 is due to the single-ion property, which is different from the quantum spin-liquid ground state observed in geometrically frustrated systems, where two-ion exchanges play an important role.

11 pages, 10 figures, 1 table