Co_0.5Ni_0.5Nb_xFe_2−xO₄ (0.00 ≤ x ≤ 0.10) nanoparticles (NPs) were prepared using the hydrothermal approach. The X-ray powder diffraction (XRD) pattern confirmed the formation of single-phase spinel ferrite. The crystallite size was found to range from 18 to 26 nm. The lattice parameters were found to increase with greater Niobium ion (Nb³⁺) concentration, caused by the variance in the ionic radii between the Nb³⁺ and Fe³⁺. Fourier transform infrared analysis also proved the existence of the spinal ferrite phase. The percent diffuse reflectance (%DR) analysis showed that the value of the band gap increased with growing Nb³⁺ content. Scanning electron microscopy and transmission electron microscopy revealed the cubic morphology. The magnetization analyses at both room (300 K, RT) and low (10 K) temperatures exhibited their ferromagnetic nature. The results showed that the Nb³⁺ substitution affected the magnetization data. We found that Saturation magnetization (M_s), Remanence (M_r), and the Magnetic moment ( $n_B$ ) decreased with increasing Nb³⁺. The squareness ratio (SQR) values at RT were found to be smaller than 0.5, which postulate a single domain nature with uniaxial anisotropy for all produced ferrites. However, different samples exhibited SQRs within 0.70 to 0.85 at 10 K, which suggests a magnetic multi-domain with cubic anisotropy at a low temperature. The obtained magnetic results were investigated in detail in relation to the structural and microstructural properties.

Tm-Tb co-substituted Co-Ni nanospinel ferrites (NSFs) as (Co_0.5Ni_0.5) [Tm_xTb_xFe_2−2x]O₄ (x = 0.00–0.05) NSFs were attained via the ultrasound irradiation technique. The phase identification and morphologies of the NSFs were explored using X-rays diffraction (XRD), selected area electron diffraction (SAED), and transmission and scanning electronic microscopes (TEM and SEM). The magnetization measurements against the applied magnetic field (M-H) were made at 300 and 10 K with a vibrating sample magnetometer (VSM). The various prepared nanoparticles revealed a ferrimagnetic character at both 300 and 10 K. The saturation magnetization (M_s), the remanence (M_r), and magneton number ($n_B$) were found to decrease upon the Tb-Tm substitution effect. On the other hand, the coercivity (H_c) was found to diminish with increasing x up to 0.03 and then begins to increase with further rising Tb-Tm content. The H_c values are in the range of 346.7–441.7 Oe at 300 K to 4044.4–5378.7 Oe at 10 K. The variations in magnetic parameters were described based on redistribution of cations, crystallites and/or grains size, canting effects, surface spins effects, super-exchange interaction strength, etc. The observed magnetic results indicated that the synthesized (Co_0.5Ni_0.5)[Tm_xTb_xFe_2−x]O₄ NSFs could be considered as promising candidates to be used for room temperature magnetic applications and magnetic recording media.

Bulk textured BiSrCaNaCuO (x = 0.0, 0.05, 0.075 0.1, 0.15, and 0.20) ceramics have been prepared by a polymer solution method followed by sinter-forging process. The microstructure and superconducting properties of textured samples were affected by Na substitution. According to XRD data, all samples show that Bi-2212 phase is the major one, and main peaks corresponded to the (00ℓ) diffractions confirming that the crystallographic c-axis is perpendicular to the surface. SEM micrographs showed that samples are composed of well-stacked and oriented grains. The best critical temperature, T, was measured as 85.6 K for x = 0.075. The critical current density Jc, values decrease gradually with the increase of applied magnetic field. The maximum calculated Jc was 1.38 × 10 A/cm at 10 K for 0.075 Na sample which is about four times higher than the 0.34 × 10 A/cm value determined for the pure sample. The anisotropic properties of these textured materials have been investigated using magnetic measurements.This work is supported by Research Fund of Çukurova University, Adana, Turkey, under grant contracts no: FBA-2014-3500. A. Sotelo and M.A. Madre acknowledge the Gobierno de Aragón and Fondo Social Europeo (Grupo de Investigacion Consolidado T12) and MINECO-FEDER (MAT2013-46505-C3-1-R) for financial support. M.A. Madre also acknowledges MINECO-FEDER (Project ENE2014-52105-R) for funding. Authors would like to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza. This work is also supported by Research Fund of Hakkari University, Turkey, under grant contracts no: MF2014BAP1.Peer Reviewe