Structural transition, electrical and magnetic properties of the B-site Co dopedSr14Cu24O41 compounds

Abstract

The effect of Co substitution for Cu on the structure and physical properties ofSr14(Cu1−xCox)24O41 compounds was studied by analyzing the selected-area electron diffraction andconvergent-beam electron diffraction patterns, and by measuring the magnetic susceptibility,the electrical resistivity and Raman spectra. It is found that the space group of theCuO2 chain ischanged from Amma toAmmm upon Co doping, butthe structure of the Cu2O3 ladder remains unchanged. This indicates that the displacement between two neighboringCuO2 chains has disappeared due to Co doping. Once a small amount of Co ions aredoped into the compound, exceptional changes in the Weiss temperature and inthe number of dimers occur. The remarkable increase in the absolute value ofthe Weiss temperature indicates that the antiferromagnetic interaction inCuO2 chains becomes very strong due to Co doping. The increase in theCurie coefficient and the number of dimers implies that the Co dopingcauses Zhang–Rice singlets in the chains to be decoupled into free spinsCu2+ and holes. Then,the free spins Cu2+ are coupled into dimers, and the holes transfer from chains to ladders, whichcauses the resistivity to decrease when the Co dopant concentration is low(x<0.10). When the Co dopant concentration is high(x>0.10), some Co ions are directly substituted for the Cu ions in the ladders, which results in anincrease in resistivity with increasing Co dopant content.