Electron-doped superconducting cuprate of Eu 2– x Ce x CuO 4+α–δ has been studied in the whole doping regime from x = 0.10–0.20 with reducing oxygen content to investigate the relation between the crystal structure and the hopping conduction in the normal state. Parameter of the crystal structure has been extracted from the X-ray diffraction (XRD) measurement while hopping conduction parameters have been obtained from resistivity measurements. The Eu–O bond length decreases with the increasing doping concentration, indicating the successful doping by the partial replacing of Eu 3+ with Ce 4+ . The resistivity increases with decreasing temperature in all measured samples. This is an indication of bad metal-like behavior in the whole regime in the normal state of electron-doped superconducting cuprate of Eu 2– x Ce x CuO 4+α–δ . The temperature dependence of resistivity was analyzed by the Arrhenius law and the variable range hopping model. It is found that the hopping conduction mechanism more likely follows the variable range hopping rather than the Arrhenius law, indicating that the hopping mechanism occurs in three dimensions. The Cu–O bond length probably plays an important role in decreasing the activation energy. The decreasing value of the activation energy correlates with the increase in the localization radius.

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The effect of nonmagnetic Zn impurities on the structural parameters and effective magnetic moment of electron-doped superconducting cuprates Eu2−xCexCu1−yZnyO4+α−δ (ECCZO) with x = 0.10 and 0.15 and y = 0 and 0.01 has been investigated using XRD and SQUID measurements. From XRD measurements, it is found that the lattice parameter of c and the Cu-O bond length increase with increasing y. The crystallite size of ECCZO samples was relatively smaller than the sample without impurities determined by the Debye–Scherrer equation and the W-H Plot method. Changes in the lattice parameters of c and Cu-O bond length can affect the appearance of superconductivity (Tc). The smaller the value of the lattice parameter of c and the Cu-O bond length causes the distance between the conducting layer and the charge reservoir to be close enough so that the charge transfer process becomes easier. From the magnetic susceptibility measurement, paramagnetic characteristics were observed for samples with x = 0.10. Meanwhile, for samples with x = 0.15, diamagnetic characteristics can be identified in sample with y = 0. The onset of Tc was observed around 11 K, as indicated by a change from paramagnetic to diamagnetic characteristics. The superconductivity phase disappears with y = 0.01. The effective magnetic moments in samples with y = 0 are smaller than those in samples with y = 0.01. The effective magnetic moment in ECCZO can be contributed by Cu2+. When the amount of Cu2+ decreases due to the addition of nonmagnetic Zn2+ atoms, the overall effective magnetic moment value also decreases. Another possibility that causes a decrease in the value of the magnetic moment of the ECCZO is the existence of stripe-pinning model, which results in suppressed superconductivity by Zn.

The samples of Eu2-xCexCuO4 (ECCO) with x = 0.09 (Eu1.91Ce0.09CuO4) and x = 0.16 (Eu1.84Ce0.16CuO4) have been synthesized by the solid reaction method without annealing. Each sample is covered with CuO to prevent excess oxygen entering the sample. The purity and electrical resistivity were investigated by x-ray Diffraction (XRD) and resistivity measurements. From the XRD analysis, it was found that the purity of ECCO phase was 93.5% with tetragonal structure of T’ for x = 0.09 while 96.1% for x = 0.16. These results show that the synthesis method with CuO covering has succeeded in synthesizing materials with high purity. From the electrical measurements, the trace of superconductors was not observed in all samples. It is probably the existence of excess oxygen, which was not fully absorbed by CuO Covering.

Graphene oxide (GO) is 2D material made of honey comb carbon structure as backbone and decorated by oxygen functional groups in both sides. These functional groups have role to the GO properties, such as magnetic susceptibility, band gap, conductivity. There are several processes to reduce its oxygen content, such as chemical, photo and thermal reduction, resulted reduced graphene oxide (rGO). Several studies reported the magnetic properties of GO and rGO correlating with the process of synthesis and reducing oxygen contents. We report the magnetic characteristic of a commercial GO 0.5 mg/ml dispersed in H2O from Graphenia and RGO that were synthesized through thermal reduction process of GO precursor. In this process, we use oven vacuum system at 200 °C for 1 hour. All samples were prepared as GO and rGO thick films. The GO and rGO samples structure were indentified from XRD data and SQUID data for magnetic characteristics. We explored the temperature dependence of magnetic susceptibility by applying magnetic field of 500 Oe in Zero Field Cooling (ZFC) and Field Cooling (FC). The result shows different susceptibility behavior of GO and rGO samples in all wide range of temperature between 0 to 300 Kelvin. The value of magnetic susceptibility rGO is higher than that of GO and has splitting curve of ZFC and FC at low temperatures below 200 Kelvin. However, GO has the splitting curve of ZFC and FC occurred at high temperatures above 200 Kelvin.