Chemical and physical pressure effects on the magnetic and transport properties of the A-Site ordered perovskite Sr₃YCo₄O _10.5

We have measured and analysed the magnetization, resistivity and thermopower of polycrystalline samples of Ca-subsituted Sr₃YCo ₄O_10.5. While the transition temperature and thermopower systematically decrease with increasing Ca content, the resistivity is nearly independent of the Ca-substitution level. We have furhter found that the substitution of Ca for Sr systematically decreases the lattice paremeters while maintaining the oxygen content unchanged, and have explained the Ca-substitution effects in terms of the spin-state transition induced by chemical pressure. We have also measured the magnetization of one of the samples under hydrostatic pressure. The result shows that the physicalpressure effect is semiquantitatively consistent with the chemical-pressure effect.