Adsorption of Al on Si(100) at high temperature

The compound Sr14Cu24O41 has a unique structure. It consists of an alternating stack of the plane containing edge-sharing CuO2 chains, and the plane containing two-leg Cu2O3 ladders sandwiched by Sr layers. The CuO2 chain also has a singlet ground state originating from a dimerization. The dimerized state in the chain depends critically on the number of holes. The effect of La substitution for Sr on the CuO2 chain spin gap is investigated by measuring the magnetic susceptibility of Sr14-xLaxCu24O41 with x less than or equal to 1. Due to the large spin gap, the Cu2O3 plane is magnetically inert below room temperature. For x=0, the susceptibility shows a characteristic decrease below 80 K, followed by an upturn below 20 K due to a Curie contribution. After subtracting the Curie term, the susceptibility is fitted by a dimer description. The dimer number N-D=1.45 and the dimer coupling constant J(D)=139 K are obtained. With increasing La content, both N-D and J(D) decrease gradually, indicating the weakening of the antiferromagnetic interaction between Cu2+ spins in the CuO2 chain. The Curie contribution enhances at the same time, and the gap feature becomes gradually smeared. It is difficult to fit the data when x=1.0. (C) 1999 American Institute of Physics. [S0021-8979(99)16308-4].