Transport and magnetic properties of the spin ladder compound Sr₁₄(Cu_1-xZnx)₂₄O₄₁

A series polycrystalline samples of Sr₁₄(Cu_1-xZn_x)₂₄O₄₁(x=0,0. 01,0. 02,0. 03) were prepared by standard solidstate reactions. X-ray diffraction(XRD) patterns show that a single phase can be achieved in all samples and their lattice parameters have weak fluctuation with the change of doping content x. X-ray photo-electron spectroscopy results show that the valence of copper ions in Sr₁₄Cu₂₄O₄₁ is + 2 and Zn doping has no effect on the valence of copper ions. Magnetic susceptibility measurements in a temperature range from 10 to 300 K show that Zn doping decreases the magnetic susceptibility of the Sr₁₄Cu₂₄O₄₁ system. Experimental fitting results show that the contribution to magnetic susceptibility of the Curie-Weiss term,the value of coupling energy in dimers J_D,the number of dimers NDand the number of free Cu²⁺ ion spins in the CuO₂ spin chain per formula unit N_F all decrease with the increase of doping content x. Further analysis indicates that the number of Zn²⁺ ions which substitute Cu²⁺ ions in dimers is less than the number of Zn²⁺ ions which substitute free Cu²⁺ ions. Electrical resistivity measurements show that the Sr₁₄Cu₂₄O₄₁ system is semiconducting,Zn doping decreases the electrical resistivity of the Sr₁₄Cu₂₄O₄₁ system,and the decreasing level increases with the increase of doping content x,but no metal-insulator transition occurs in this system. We think that the decrease in electrical resistivitymaybe results from decoupling of dimers in the spin chain due to Zn²⁺ ion doping. It means that the charge order super structure is destroyed,so more holes are released and transferred into the spin ladder then participate in conducting.