Spin dynamics and magnetic excitations of quasi-1D spin chain Ca$_3$ZnMnO$_6$

Abstract

To reveal the structure-property relationship in quasi-one-dimensional (1D) spin-chain system Ca$_3$ZnMnO$_6$, we present comprehensive results, combining basic physical characterizations such as muon spin relaxation/rotation ($\mu$SR), neutron powder diffraction (NPD), inelastic neutron scattering (INS), and theoretical calculations. Ca$_3$ZnMnO$_6$ features a dominant intrachain coupling $J_1$ and two distinct interchain interactions $J_2$ and $J_3$, and it undergoes antiferromagnetic ordering below $T_{\mathrm{N}}=25$~K, as revealed by dc magnetic susceptibility and specific-heat measurements. Zero-field $\mu$SR shows persistent spin dynamics below $T_{\mathrm{N}}$, suggesting unconventional magnetic excitations in the ordered state. NPD results indicate a commensurate magnetic ground state with a propagation vector $\mathbf{k}=0$, where the Mn spins lie in the $ab$-plane. INS spectra display dispersive magnetic excitations extending up to about 5~meV, with an energy gap smaller than 0.5~meV. Notably, these spectra exhibit three-dimensional (3D) gapped features rather than the expected 1D behavior, yet spin-wave dispersion analysis confirms an underlying quasi-1D energy hierarchy. We discuss this apparent paradox of 3D-like magnetic excitations in a quasi-1D system in terms of the energy hierarchy modified by nonmagnetic-ion substitution and finite-temperature first-principles calculations. We also suggest that Ca$_3$ZnMnO$_6$ could be a potential candidate for an M-type altermagnet.