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    Influence of temperature and selenium substitution on electrical and dielectric characteristics of CoFe2O4 nanoparticles
    (Elsevier B. V., 2025) Ünal, Bayram; Baykal, Abdülhadi; Almessiere, M. A.; Mihmanlı, Ahmet
    This study investigates the influence of Se⁴⁺ ion substitution on the electrical and dielectric properties of CoFe2O4 nanoparticles (CoFe2-4xSe3xO₄ (x ≤ 0.1) (NPs)) synthesized via a hydrothermal method. The electrical and dielectric characteristics were analyzed using a Novocontrol dielectric impedance analyzer. Results indicate that activation energies (Ea) remain stable at approximately 600 meV at higher temperatures (T ≥ 45 ◦C) but decrease significantly at lower temperatures, ranging from 300 meV (x = 0.02) to 20 meV (x = 0.08). A sharp reduction in DC conductivity, from 1.2 nS/cm (x = 0.04) to 0.27 nS/cm (x = 0.08), suggests enhanced electron mobility at this substitution level. AC conductivity exhibits strong frequency dependence, increasing from 0.15 nS/cm at 1 kHz to 0.13 μS/cm at 1 MHz for x = 0.08 at room temperature. Dielectric constant (ε′) and loss (ε′′) values exhibit significant variation with frequency, with ε′ reaching a maximum of 3.95 at 100 Hz for x = 0.08, reflecting enhanced polarization effects. Se⁴⁺ substitution also increases the real part of the electrical modulus (ReM) to 0.99 and the imaginary part (ImM) to 0.40 for x = 0.10, indicating improved energy storage and dissipation capabilities. The ImZ/ReZ ratio analysis reveals shifts in conduction mechanisms and polarization effects, with a notable transition at x = 0.04. Cole-Cole plots suggest multiple relaxation processes influenced by temperature and substitution levels, with relaxation times decreasing from 13 ms (70 ◦C) to 0.76 ms (120 ◦C) for x = 0.02. This study highlights the potential of Se⁴⁺-substituted Co-SFs for applications in electronic devices, particularly in energy storage and dissipation systems, and underscores the need for combined experimental and theoretical approaches to optimize these materials for advanced technological applications.
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    Tunned the structure and magnetic characteristics of noble metal (Pd)-doped Ba-Sr nanohexaferrites
    (Elsevier B. V., 2025) Algarou, N. A.; Aldakheel, R. K.; Almessiere, M. A.; Baykal, Abdülhadi; Güngüneş, H.; Çalışkan, S.; Mihmanlı, Ahmet
    In this study, various ratios of Pd-doped Ba-Sr nanohexaferrites (NHFs) were studied. All samples were produced via sol–gel combustion and were designated as Ba0.5Sr0.5Pd3xFe12-2xO19 (x ≤ 0.1) NHFs. Detailed examinations of the magnetic and structural features were conducted. X-ray diffraction (XRD) confirmed the presence of a M-type HF phase, along with a small phase of iron oxide (Fe2O3) for some doping ratios. Both the SEM and TEM (Scanning and Transmission electron microscope respectively) revealed the formation of the hexagonal platelet morphology. The hyperfine parameters were determined by using Mossbauer ¨ spectroscopy. Pd2+ ions substituted Fe3+ ions at 12k site. The crystal symmetry not influenced by substitution. Fe3+ charge state was detected all samples. Magnetic properties are investigated through hysteresis loop analysis at room temperature (RT) and 10 K. Ms (saturation magnetization), Mr (remanence), Hc (coercivity), SQR (squareness ratio), and nB (experimental magnetic moment), were evaluated as a function of Pd doping. The pristine sample exhibited hard ferrimagnetic behavior with high Hc and Mr, while Pd-doped samples demonstrated reduced magnetic properties. Particularly, intermediate Pd concentrations (x = 0.04 and 0.06) resulted in slight increases in Ms. SQR values signify multidomain and single-domain nature for Pd-doped and undoped samples, respectively. XPS’ (X-ray photoelectron spectroscopy) broad spectrum of energies verified the presence of Ba, Sr, Pd, Fe, and O in the product.