Spin-state transition of Co ion (25/2) in hole substituted 1D chain of CaCoO.

We have discovered spin-state transition (= 2 to= 5/2) of Co ions due to Mg substitution in the CaCoOapparent in the magnetic susceptibility, x-ray photoelectron spectroscopy (XPS), and first-principles study. We also examine the effect of Mg substitution on the magnetic and electronic structure of CaCoOby first-principles calculations. It involves generalized gradient approximation with Coulomb interaction () in exchange-correlation energy functional. Our study shows a reasonable agreement between effective magnetic moment () determined from the Curie-Weiss fit with that from the XPS analysis and first-principles calculations study. We have attributed the decrease in positive intra-chain exchange interaction constant (/) to the antiferromagnetically coupled induced Coions (= 5/2) arising from the Mgions substitution. The in-field metamagnetic transitions in the isothermal() curves below the critical field () have been accurately mapped and successfully explained by the change in magnetic entropy (Δ) calculations and Arrott plots. Electronic structure study reveals hole-type doping of Mg atom, and the Fermi level () shifts below. Density of state and band structure calculation indicates strong hybridization between partial states of Co-3d and O-2p orbitals for the Mg-doped compound due to which the band crossing at Fermi level is observed, and a hole-type Fermi surface is formed.