自旋梯状化合物Sr14(Cu1-xZnx)24O41的电输运及磁学性质

采用标准固相反应法制备了Sr14(Cu1-xZnx)24O41(x=0, 0. 01, 0. 02, 0. 03)系列多晶样品. X射线衍射谱表明所有样品均呈单相,且样品晶格常数大小随Zn掺杂量x的变化存在微弱波动. X射线光电子能谱表明Sr14Cu24O41中Cu离子以+2价形式存在,Zn掺杂对体系中Cu离子化合价不造成影响. 磁化率测量结果表明在10~300 K温度范围内Zn掺杂使体系磁化率降低,拟合结果表明随着Zn掺杂量x的增大,居里-外斯项对体系磁化率贡献逐渐减弱,二聚体耦合能JD 逐渐降低,每个分子中CuO2 自旋链内二聚体个数ND 与自由Cu2+离子自旋数NF 均逐渐减少,进一步分析显示替换二聚体内Cu2+离子的Zn2+离子数少于替换自由Cu2+离子的Zn2+离子数. 电阻率测量结果表明Sr14Cu24O41体系具有半导体特性,并且Zn掺杂会使体系电阻率降低,降低程度随掺杂量x增大而增大,但并未使体系发生金属- 绝缘体转变. 认为电阻率降低可能是由于Zn2+离子掺杂使体系内CuO2 自旋链中二聚体发生退耦,破坏了电荷有序超结构,从而使更多的空穴释放出来并转移到导电性好的Cu2O3自旋梯子中所致.

Transport and magnetic properties of the spin ladder compound Sr14(Cu1-xZnx)24O41

A series polycrystalline samples of Sr14(Cu1-xZnx)24O41(x=0, 0. 01, 0. 02, 0. 03) were prepared by standard solid-state 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 JD , the number of dimers ND and the number of free Cu2+ ion spins in the CuO2 spin chain per formula unit NF 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 Sr14 Cu24O41 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 resistivity maybe 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.