SPIN-STATE TRANSITION IN LAYERED PEROVSKITE COBALT OXIDES - LA2-XSRXCOO4 LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1.0)

Magnetic and transport properties are investigated for single crystals of layered perovskite cobalt oxides, La2-xSrxCoO4 (0.4 less than or e qual to x less than or equal to 1.0). The effective magnetic moment mu (eff) is found to decrease with increasing x (or increasing the number of Co3+ ions) from approximate to 4.0 mu(B) for x=0.4-0.5 to approxim ate to 2.6 mu(B) for x=0.8-1.0, accompanied by a steep reduction of th e resistivity rho(ab) and Wiess temperature circle dot. These drastic changes of the magnetic and electronic properties suggest a spin-state transition of the Co3+ ions from the high-spin to the intermediate-sp in state.