Reduced magnetic disorder at low temperature in Ca3Co2O6 via zinc substitution

The compound Ca3Co2O6 undergoes a transition into a spin-density wave (SDW) state near 24 K. Below similar to 10 K, this unstable SDW state coexists with a nearly- degenerate commensurate antiferromagnetic state as well as short-range magnetic order. Clear signatures of this strong magnetic disorder have been observed in the response of entropy to changing magnetic field and temperature. We performed a calorimetry study of Ca3Co2O6 and Ca3Co1.9Zn0.1O6 in order to compare their entropic responses at low temperature. Our results for Ca3Co2O6 reveal that Delta S(T, H) equivalent to S(T, H)-S(T, H = 0) increases as either temperature or magnetic field increase. In contrast, Delta S data for Ca3Co1.9Zn0.1O6 were relatively unresponsive to changes in temperature or field, suggesting that Zn substitution may reduce the low-temperature magnetic disorder observed in Ca3Co2O6. These results are discussed within the context of two cases (Ca3Co2O6 under applied pressure and Ca2.75R0.25Co2O6 (R = Dy, Lu)) in which a single magnetic ground state is stabilised.