Papers by Keyword: Electron-Doped

Abstract: High-Temperature Superconductor Cuprates (HTSC) are materials that exhibit superconductivity at higher temperatures compared to conventional superconductors. The effect of impurities in HTSC in the overdoped region is very important to study because there are interesting phenomena such as the spin-glass state. In this study, we have synthesized Eu₂₋_(x+y)Ceₓ_-yCu₁₋_yFe_yO₄₊_α₋δ (ECCFO) materials with x = 0.18; 0.19; 0.20; 0.21 and 𝑦 = 0; 0.03 using the solid-state reaction method to study the effect of Fe impurities on the crystal structure and magnetic properties in the overdoped region. The crystal structure was characterized using XRD measurements, and the magnetic properties were characterized using SQUID measurements at temperatures of 2 K to 30 K with a magnetic field of H = 5 Oe. The XRD measurement results show that all samples have a tetragonal T' structure, which corresponds to the ECCO crystal structure. The values of the lattice parameter c, unit cell volume, and CuO bond length increase with increasing y. From the SQUID measurements, for y = 0 with x = 0.19; 0.20, shows superconducting properties with T_c onset around 11 K. For variation y = 0.03 with x = 0.18; 0.20; 0.21, antiferromagnetic-like properties were observed, while the samples with x = 0.19 shows paramagnetic properties. These results indicate that Fe as a magnetic impurity affects spin arrangement in the conduction layers, as evidenced by an increase in the Curie constant and the effective magnetic moment.

Abstract: The suppression of superconductivity (T_c) in electron-doped superconducting materials Eu_1.81Ce_0.19Cu_1-yZn_yO_4+α-δ (ECCZO) heavily overdoped regimes by nonmagnetic impurity Zn with concentration of y = 0, 0.01, 0.02, and 0.03 has been successfully investigated by using XRD and SQUID measurements. All samples were synthesized using the solid-state reaction method. The crystal structure obtained from XRD measurements has a tetragonal T° structure, which matches the crystal structure of electron-doped superconductors in general. The addition of Zn impurity shows no change in the crystal structure, but there is a decrease in the α-lattice and an increase in the c-lattice, unit cell volume, and Cu-O bond length. This causes the distance between the charge reservoir and the conduction layer to increase and affects the disappearance of T_c. Magnetic susceptibility measurements using SQUID were carried out under FC (Field Cooling) conditions with temperatures between 2 - 30 K with a field of 5 Oe. The sample with y = 0 has diamagnetic properties with a superconductivity value (T_c) of about 11 K. The addition of Zn impurities succeeded in suppressing superconductivity as indicated by the disappearance of T_c, so that the sample is in the ground state. The Curie constant and the effective magnetic moment decrease with increasing Zn concentration. This is probably due to the decrease in Cu²⁺ when the non-magnetic Zn²⁺ atoms were added, therefore the overall value of the µ_eff decreases when Zn²⁺ substitutes some Cu²⁺. This result is different from that described by Abrikosov-Gor’kov theory in the hole-doped high-T_c cuprates.

Abstract: The normal state of high-T_c superconducting cuprates is crucial to understanding of the mechanism in superconductivity. There are two main ways to remove superconductivity so that the sample is in a normal state, that is by applying a large magnetic field or adding impurities such as Zn to the sample. To investigate the crystal structure and magnetic properties in the normal state of electron-doped high-T_c cuprates in overdoped regime, Eu_2-xCe_xCu_0.97Zn_0.03O_4+α-δ (ECCZO) with x = 0.16, 0.17, 0.18, and 0.19 has been synthesized by the solid-state reaction method. The crystal structure and magnetic properties of the samples were characterized by XRD and SQUID measurements. The results of XRD measurements shows all samples have T’-structure and the values of lattice parameters a, CuO bond length, and crystallite size increased with increasing x. On other hand, the value of lattice parameters c decreased with increasing x, causing the expansion of the tetragonal unit cell in the horizontal direction. From susceptibility measurements, in the normal state with 3% of Zn impurity all samples have the paramagnetic behaviour. The magnetic parameters of these samples analysed by the Curie law. With increasing of Ce concentration, the C and the are increased. The increase in the magnetic parameters since the increasing in magnetic ordering.

Abstract: We have succeeded in synthesizing electron-doped cuprates T’-Pr_2-xCe_xCuO₄ (PCCO) with x = 0 and 0.10 nanocrystals prepared by the chemically dissolved method. Reduction annealing of the PCCO samples at 700°C under a flowing argon gas atmosphere has been performed for the removal of excess oxygen in the apical sites. The XRD data showed that the reduction annealing process decreases c-axis length indicating successful removal of the excess oxygen. The bond distortion of PCCO including coordination number and bond distance between the absorber atoms with the nearest neighboring atoms (Cu-O) was investigated by extended x-ray absorption fine structure (EXAFS) using Cu K-edge. The implication of our results is discussed on the basis of tremendous influence of oxygen vacancies on the magnetism of the nanosized T’-cuprates at the normal state.

Abstract: Thin films of perovskite manganite La_0.9Hf_0.1MnO₃ (LHMO) have been grown on (100) SrTiO₃ single-crystal substrates with different growth pressures by pulsed laser deposition. The different transport behaviors of films have been fitted by various models. The results clearly demonstrate that oxygen pressure is an efficient way to change the transport behaviors of LHMO films. All the transport behaviors observed in LHMO films can be better fitted by Mott’s variable range hopping model than the other two models.

Abstract: The magnetotransport behaviors of electron-doped colossal magnetoresistance (CMR) manganites La0.9Te0.1MnO3 have been investigated in external magnetic fields up to 4 T. The temperature dependence of the resistivity shows that the transport mechanisms of the sample below the metal-insulator transition temperature are attributed to the electron-phonon and magnon scattering behaviors. While the resistivity above Curie temperature (Tc=240 K) can be fitted with either polaron transport or variable-range hopping, and the fitting results are affected significantly by the magnetic fields. The electron spin resonance investigation indicated that there exist the ferromagnetic clusters up to 280 K in the paramagnetic phase of the sample. As a result, a possible correlation between the resistivty and phase separation is considered.