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自旋梯狀化合物Sr14(Cu1-xZnx)24O41的電輸運及磁學性質

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

  • 摘要: 采用標準固相反應法制備了Sr14(Cu1-xZnx)24O41x=0,0.01,0.02,0.03)系列多晶樣品.X射線衍射譜表明所有樣品均呈單相,且樣品晶格常數大小隨Zn摻雜量x的變化存在微弱波動.X射線光電子能譜表明Sr14Cu24O41中Cu離子以+2價形式存在,Zn摻雜對體系中Cu離子化合價不造成影響.磁化率測量結果表明在10-300 K溫度范圍內Zn摻雜使體系磁化率降低,擬合結果表明隨著Zn摻雜量x的增大,居里-外斯項對體系磁化率貢獻逐漸減弱,二聚體耦合能JD逐漸降低,每個分子中CuO2自旋鏈內二聚體個數ND與自由Cu2+離子自旋數NF均逐漸減少,進一步分析顯示替換二聚體內Cu2+離子的Zn2+離子數少于替換自由Cu2+離子的Zn2+離子數.電阻率測量結果表明Sr14Cu24O41體系具有半導體特性,并且Zn摻雜會使體系電阻率降低,降低程度隨摻雜量x增大而增大,但并未使體系發生金屬-絕緣體轉變.認為電阻率降低可能是由于Zn2+離子摻雜使體系內CuO2自旋鏈中二聚體發生退耦,破壞了電荷有序超結構,從而使更多的空穴釋放出來并轉移到導電性好的Cu2O3自旋梯子中所致.

     

    Abstract: A series polycrystalline samples of Sr14(Cu1-xZnx)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 JD,the number of dimers NDand 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 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.

     

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