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

Mossbauer and magnetization have been measured for the samples Ca 3 (Co 1-x M x ) 2 O 6 , M = 57 Fe and Zn, with triangular lattice consisting of 1-D ferromagnetic chains. For the sample of x = 0.01 (M = Fe), a broad splitting Mossbauer 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 57 Fe 3+ 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 Fe 3+ spin fluctuation. It is concluded that the substitution of Fe-impurity cuts the ferromagnetically ordered linear chains and, consequently, the Ising nature of Co 3+ spins is much weakened, which provides a new relaxation path for Fe-spin fluctuation.