Spin freezing and dynamics in Ca3Co2-xMnxO6 (x≈0.95) investigated with implanted muons: Disorder in the anisotropic next-nearest-neighbor Ising model

We present a muon-spin relaxation investigation of the Ising chain magnet Ca3Co2-xMnxO6 (x approximate to 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 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-SF approximate to 8 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.