Chromium site selective substitution in Ca3Co2O6:: Influence on the magnetic properties of an Ising-like triangular lattice -: art. no. 094418

The structure of the Ca3Co2O6 compound is made of chains on a triangular array. The intra- and interchain coupling are ferromagnetic and antiferromagnetic, respectively, and the chain itself contains a 1:1 alternation of CoO6 trigonal prisms (TP) and octahedra (oct.). The Co3+ spin states are high spin (S=2) and low spin (S=0) in the TP and the oct., respectively. It is found that a few percent of Cr3+ (S=3/2) substituted for the low spin Co-oct(3+) (S=0) greatly affect the magnetic properties. Both coupling constants of the antiferromagnetic (interchain) and ferromagnetic (intrachain) interactions decrease as x increases up to x=0.10 in Ca3Co2-xCrxO6. This is reflected by the decrease of the magnetization saturation and of the magnetic field characteristic of the ferri- to ferromagnetic transition, below the Neel temperature. These results are interpreted on the basis of an antiferromagnetic coupling between Co-oct(3+) and its high spin Co-TP(3+) neighbours. Furthermore, the magnetization jumps, observed below T<10 K, tend to be suppressed on the isothermal magnetization curves as soon as x=0.05. These results emphasize the great sensitivity of the Ca3Co2O6 magnetic behavior to the presence of a magnetic foreign cation, with, in particular, a T-N decrease probed by specific-heat measurements.