Physical Properties and Magnetic Anisotropy in Ferromagnetic Superconductor RuSr2GdCu2O8 and Iron-based SmFeAsO system

• Main Authors: Chang, Bin-Chang, 張炳章
• Other Authors: Ku, Huan-Chiu
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/50155052352469075585

博士 === 國立清華大學 === 物理學系 === 97 === In this research, we studied the physical properties and their anisotropy of ferromagnetic superconductor RuSr2GdCu2O8 and iron-based SmFeAs(O1-x,Fx). Both compounds exhibit superconductivity at low temperature. For RuSr2GdCu2O8, the ferromagnetic transition at Tmag(Ru5+/4+) = 131 K and the superconducting transition at Tc(dia) = 39 K in CuO2 plane were observed. A lower transition with TN(Gd) = 2.5 K was also observed. A phase diagram was generated from resistivity and magnetic measurements. The crystal structure, magnetism, specific heat, and electric property were discussed. A metal-insulator transition boundary around Sm was observed. Further study was carried out to investigate the anisotropy of the ferromagnetic superconductor. For the semimetal SmFeAsO, a transition temperature of 140 K was obtained. The superconducting onset temperature Tc(onset) of 40 K and zero resistivity Tc(zero) of 20 K were observed for SmFeAs(O0.6F0.2) sample. Due to spin-orbit related anisotropy in paramagnetic susceptibility, cab(Fe) > cc(Fe) at 300 K in (Sm0.95La0.05)FeAs(O0.85F0.15) powder, a grain-aligned sample can be achieved using field-rotational method. The anisotropy of 0.83 in the paramagnet at 300 K increased to 3 in the superconducting state at 2 K. The grain alignment in magnetic field was based on the principle of magnetic anisotropy which is relative to the spin order with the orbit order of grain. The spin order drives orbit order of the grain. The sample of aligned grains was studied for anisotropic paramagnet, anisotropic superconductivity, and anisotropic X-ray absorption near edge spectra.