Moessbauer study of impurity effect on ferrimagnet Ca3Co2O6 with 1-D ferromagnetic chains

Moessbauer and magnetization have been measured for the samples Ca3(Co1-xMx)2O6, M=57Fe and Zn, with triangular lattice consisting of 1-D ferromagnetic chains. For the sample of x=0.01 (M=Fe), a broad splitting Moessbauer spectrum appears around 40 K and changes to the one consisting of three sextets below 30 K, which can be attributable to the slow relaxation of 57Fe3+ spins embedded in the 1-D chains of Co with strong anisotropy. A comparison of the spectra between x=0.01 (M=Fe) and 0.05 (Fe) samples reveals that increase of Fe-impurity enhances Fe3+ spin fluctuation. It is concluded that the substitution of Fe-impurity cuts the ferromagnetically ordered linear chains and, consequently, the Ising nature of Co3+ spins is much weakened, which provides a new relaxation path for Fe-spin fluctuation