Papers by Keyword: Magnetic Impurities

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 researching of dependence of magnetization from temperature T and magnetic field in the Bi₂Fe_0.128Te_2.844Se_0.145 single-crystal showed that it have spinglass-like state with freezing temperature T_f= 40 K. Its electric resistance up to 100 K is ~ 10³ Ohm and decreases with the temperature increase. At T > 110 K electric resistance ~ 10^-2 Ohm and magnetization is four times smaller than in spinglass-like state. It can be assumed from these results that this sample is topological insulator at T > 110 K and at small temperature, where it is spinglass-like, offers the breaking of the time reversal symmetry.

Abstract: We carried out a theoretical investigation on the properties of manganese impurity centers in cubic boron and gallium nitrides. The calculations were performed using the all electron spin-polarized full-potential linearized augmented plane wave methodology. Our results indicate that manganese in boron nitride, in a neutral charge state, is energetically more favorable in a divacancy site as compared to a substitutional cation site. We present the results on stability, spin states, impurity magnetic moment, hyperfine parameters, and formation and transition energies of manganese at the divacancy site in several charge states.

Abstract: The electronic and structural properties of isolated 3d-transition metal impurities in 3C, 4H, and 2H silicon carbide have been investigated bytotal energy ab initio methods. The stability, spin states and transition energies of substitutional (Si sub-lattice) Cr, Mn, and Fe impurities in several charge states were computed. Our results are discussed in the context of available experimental data.