Negative chemical pressure effects induced by Y substitution for Ca on   the exotic magnetic behavior of spin-chain compound, Ca3Co2O6
  The magnetic behavior of a solid solution, Ca3-xYxCo2O6, based on an exotic spin-chain compound, Ca3Co2O6, crystallizing in K4CdCl6-derived rhombohedral structure is investigated. Among the compositions investigated (x= 0.0, 0.3, 0.5, 0.75 and 1.0), single phase formation persists up to x= 0.75, with the elongation of the c-axis. The present investigations reveal that the temperature at which the partially disordered antiferromagnetic structure sets in (which occurs at 24 K for the parent compound, x= 0.0) undergoes gradual reduction with the substitution of Y for Ca, attaining the value of about 2.2 K for the nominal x = 1.0. The trend observed in this characteristic temperature is opposite to that reported under external pressure, thereby establishing that Y substitution exerts negative chemical pressure. Anomalous steps observed in the isothermal magnetization at very low temperatures (around 2 K) for x= 0.0, which have been proposed to arise from quantum tunneling effects are found to vanish by a small substitution (x = 0.3) of Y for Ca. Systematics in ac and dc magnetic susceptibility behavior with Y substitution for Ca have also been probed. We believe that the present results involving the expansion of chain length without disrupting the magnetic chain may be useful to the overall understanding of the novel magnetism of the parent compound. 
S. Rayaprol and E.V. Sampathkumaran