Spin freezing and dynamics inCa3Co2−xMnxO6(x≈0.95)investigated with implanted muons: Disorder in the anisotropic next-nearest-neighbor Ising model

Abstract

We present a muon-spin relaxation investigation of the Ising chain magnet ${\text{Ca}}_{3}{\text{Co}}_{2\ensuremath{-}x}{\text{Mn}}_{x}{\text{O}}_{6}$ $(x\ensuremath{\approx}0.95)$. We find dynamic spin fluctuations persisting down to the lowest measured temperature of 1.6 K. The previously observed transition at around $18\text{ }\text{K}$ is interpreted as a subtle change in dynamics for a minority of the spins coupling to the muon that we interpret as spins locking into clusters. The dynamics of this spin fraction freeze below a temperature ${T}_{\text{SF}}\ensuremath{\approx}8\text{ }\text{K}$, while a majority of spins continue to fluctuate. An explanation of the low-temperature behavior is suggested in terms of the predictions of the anisotropic next-nearest-neighbor Ising model.