Yazar "Ayas, Ali Osman" seçeneğine göre listele

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    Effect of B site partial Ru substitution on structural magnetic and magnetocaloric properties in La0.7Pb0.3Mn1-xRuxO3 (x=0.0, 0.1 and 0.2) perovskite system
    (Elsevier, 2020) Ayas, Ali Osman; Cetin, Selda Kılıç; Akyol, Mustafa; Akca, Gonul; Ekicibil, Ahmet
    The La0.7Pb0.3Mn1-xRuxO3 (x = 0.0, 0.1 and 0.2) perovskite manganite compounds have been fabricated by solid-state reaction method to investigate structural, magnetic and magnetocaloric properties. All samples are indexed in the Rhombohedral structure with R (3) over tildec space group by using the Rietveld refinement method. The Curie temperature decreases from 336 K to 313 K when Ru (x = 0.1) is added to the structure and it becomes 335 K for x = 0.2. Maximum magnetic entropy change and relative cooling power values were calculated as 3.17, 3.15, 3.06 J kg(-1) K-1 for 5 T magnetic field change and 214.40, 160.20, 128.38 J kg(-1) under 4 T magnetic field change for x = 0.0, 0.1 and 0.2 in La0.7Pb0.3Mn1-xRuxO3, respectively. From the H/M vs M-2 plots obtained from isothermal magnetization curves, it is found that all samples exhibit a second-order magnetic phase transition, which shows reversible magnetocaloric effect. Under the light of all observed results, La0.7Pb0.3Mn1-xRuxO3 (x = 0.0, 0.1 and 0.2) perovskite manganite compounds can be considered as candidate materials above room temperature range magnetic cooling systems. (C) 2019 Elsevier B.V. All rights reserved.
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    Effect of boron content on structure and magnetic properties in CoFe2O4 spinel nanocrystals
    (Elsevier Science Sa, 2018) Akyol, Mustafa; Adanur, Idris; Ayas, Ali Osman; Karadag, Faruk; Ekicibil, Ahmet
    We study the effect of boron content on the structural and magnetic properties of CoFe2O4 spinel nanocrystallines synthesized by sol-gel method. The crystal structure and phase identification of samples are studied by using X-ray diffraction experiment and Rietveld analysis. Rietveld refinement results reveal that all samples have cubic symmetry with space group Fd3m. The cationic distributions are obtained from Rietveld refinement that boron ions are settled into both tetrahedral and octahedral sites in spinel lattice. The crystallite sizes of samples are found in a range of 47-67 nm that is in the limit of single domain in such structure. All samples show ferromagnetic nature and magnetic transition was not seen in the temperature range of 5-400 K. The magnetic domains are pinned with adding boron ions into the CoFe2O4 spinel structure at low temperatures. Thus, an increment in the propagation field (H-p) and temperature (T-p) by boron content in CoFe2O4 structure is observed. In addition, the saturation magnetization (M-s) normalized by crystal size increases with increasing boron concentration. The temperature dependence of magnetic properties of the samples taken by experimental data are confirmed with the Neel-Arhenius model by adding thermal dependence of magnetocrystalline anisotropy term. The results indicate that boron-doping into the spinel structure enhances ferromagnetic coupling and suppresses super-exchange interaction between tetrahedral (X) and octahedral (Y) sites. (C) 2018 Elsevier B.V. All rights reserved.
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    Effect of Ho substitution on structural, magnetic and magnetocaloric properties of Co(CrFe)O4
    (Springer, 2021) Kivrak, Burak; Gulkesen, Semiramis; Ayas, Ali Osman; Akyol, Mustafa; Ekicibil, Ahmet
    In this study, structural, magnetic and magnetocaloric properties of Ho-substituted Co(CrFe)O-4 spinel compounds produced by the sol-gel method were investigated. The Ho concentration in Co(CrFe)O-4 spinel structure was changed from 0 to 20% by 5% steps. It is observed that the Ho3+ ions create a new phase HoCrO3/HoFeO3 in the host spinel lattice. SEM images of samples indicate that the average particle size increases with Ho content. The paramagnetic to ferro-/ferrimagnetic phase transition temperature increases from 312 to 344 K with Ho content. While the fluctuation in saturation magnetization of samples was detected at low temperature, it almost becomes a linear change with the Ho content. The maximum magnetic entropy change under 7 T magnetic field was found as - 1.39, - 1.50, - 1.20, - 0.98 and - 0.91 J/kgK for Ho-free, 5, 10, 15 and 20 wt% Ho content in CoCrFeO4 spinel structure, respectively.
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    Effects of Ca substitution on magnetic and magnetocaloric properties in PrBa1-xCaxMn2O6 system
    (Academic Press Inc Elsevier Science, 2023) Kandemir, Arda; Akca, Gonul; Cetin, Selda Kılıç; Ayas, Ali Osman; Akyol, Mustafa; Ekicibil, Ahmet
    In this study, we have examined the effect of Ba substitution by Ca on the magnetic, and magnetocaloric properties of PrBa1-xCaxMn2O6 (x = 0, 0.2 and 0.3) double perovskite manganites produced using sol-gel method. The samples were indexed in orthorhombic structure (with space group of Pbnm). The temperature-dependent magnetization, M(T), measurements indicate that all samples have a magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) state with increasing temperature. Curie temperature (T-C) decreases with increasing Ca content in the main lattice. From the magnetic field dependence of magnetization measurements, M(H), maximum magnetic entropy change (-Delta S-M(max)) values were calculated as 4.07, 4.12, and 5.04 Jkg(-1)K(-1) under 5 T for PrBaCaMn2O6, PrBa0.8Ca0.2Mn2O6, and PrBa0.7Ca0.3Mn2O6 samples, respectively. Relative cooling power (RCP) values below 5 T were determined as 214.16, 227.14 and 279.62 Jkg(-1) based on the increasing Ca content. The -Delta S-M(max) and RCP values enhance with increasing Ca content, respectively. The nature of the phase transition, checked by Banerjee criterion and Franco's universal master curves, was found to be second order magnetic phase transition (SOMT).
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    Investigation of the effect of sintering temperature on structural, magnetic and magnetocaloric properties in PrCaMn2O6 double perovskite manganite system
    (Springer, 2022) Ayas, Ali Osman; Kandemir, Arda; Cetin, Selda Kılıç; Akca, Gonul; Akyol, Mustafa; Ekicibil, Ahmet
    We have studied the effect of sintering temperature change on structural, magnetic and magnetocaloric properties of PrCaMn2O6 compound. The samples were produced by using solid-state-reaction process and then sintered at 1000, 1100 and 1200 degrees C temperatures. The Rietveld refinement results indicate that the crystal symmetry of the produced samples is tetragonal with P4mm space group. All samples include impurity phase, and their percentages decrease with increasing sintering temperature. Scanning electron Microscope images show that grain sizes of samples increase with increasing T-S. Energy-dispersive X-ray spectra indicate that samples include all required starting elements. Temperature-dependent magnetization measurements show that samples have the Curie temperatures as 42.6, 43.1, and 42.8 K for samples sintered at 1000, 1100 and 1200 degrees C, respectively. Magnetic entropy change values are found as 1.19, 1.59 and 1.72 J kg(-1) K-1 at 5 T magnetic field change for samples sintered at 1000, 1100 and 1200 degrees C, respectively. Relative cooling power values are calculated as 14.28, 20.54 and 17.20 J kg(-1) for samples sintered at 1000, 1100 and 1200 degrees C, respectively. The universal curve and the Arrott plots show that magnetic phase transition type of all samples is second order.
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    Magnetic field dependence of magnetic coupling in CoCr2O4 nanoparticles
    (Elsevier, 2017) Akyol, Mustafa; Adanur, Idris; Ayas, Ali Osman; Ekicibil, Ahmet
    CoCr2O4 spinel nanoparticles synthesized by sol-gel method have been worked extensively by performing structural and magnetic characterization techniques, as well as modeling the experimental results. The microstructure analysis shows that the crystallite size of CoCr2O4 nanoparticles, which are purely crystallized in cubic phase with space group Fd3m, is similar to 75 nm. The grain size distribution determined from scanning electron microscope images indicates that the particles are uniformly formed and distributed homogenously in the structure. A comprehensive magnetic study has been performed by measuring magnetic moment as a function of temperature and external magnetic field. The paramagnetic to ferromagnetic phase transition and non-collinear spiral magnetic transition have been observed in CoCr2O4 nanoparticles at 96 and 27 K, respectively. Interestingly, we observed field-condition shift in lock-in transition which is found as 16 and 8 K for FH and FC, respectively. The exchange bias effect is observed when the CoCr2O4 sample is cooled under magnetic field. The magnitude of exchange bias field decreases with increasing temperature from 5 to 50 K, and it is vanished above 50 K. In addition, we also worked on the magnetic entropy change around the paramagnetic to ferromagnetic phase transition. The magnetic entropy change is found as -0.87 J/kg K under 6 T magnetic field.
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    Magnetic refrigeration: Current progress in magnetocaloric properties of perovskite manganite materials
    (Elsevier, 2023) Ayas, Ali Osman; Cetin, Selda Kılıç; Akca, Gonul; Akyol, Mustafa; Ekicibil, Ahmet
    Magnetic cooling technology based on the magnetocaloric effect is a prominent research topic due to its great potential helps to solve the increasing energy need and environmental problems arising from existing technologies. Studies on magnetic cooling systems mainly include both engineering works and material research activities. This review principally covers the material research part of these studies and presents the current developments in them. Specifically, this review focuses on perovskite manganites due to their various advantages over other material families, such as large working temperature range, adjustable Curie temperature, easy production methods and low costs, chemical stability, negligible thermal and magnetic hysteresis properties. In accordance with these properties, important research points such as crystal structure, mismatch effect, magnetic properties, etc., related to the perovskite manganite materials are evaluated and interpreted. Additionally, progress on some prominent material families rather than perovskites is also briefly discussed.
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    Magnetocaloric effect in PrGd1-xBaxMn2O6 (0.0 ? x ? 1.0) double perovskite manganite system
    (Springer, 2023) Akca, Gonul; Kandemir, Arda; Ayas, Ali Osman; Kılıç Cetin, Selda; Akyol, Mustafa; Ekicibil, Ahmet
    The PrGd1-xBaxMn2O6 (x = 0.0, 0.6, 0.7, 0.8, 0.9, 1.0) double-perovskite manganite samples produced by solid-state reaction method have been investigated in this study. The samples were crystallized in the form of orthorhombic structure with the Pbnm space group confirmed by the Rietveld refinement method. The temperature-dependent magnetization measurements (M(T)) revealed that the samples display a phase transition from ferromagnetic to paramagnetic as temperature increased. The results obtained from these measurements indicate that the Curie temperature values increased from 44 to 187.8 K, respectively, by increasing the Ba concentration from x = 0.0-1.0. The isothermal magnetization curves are achieved by external magnetic field-dependent magnetization measurements (M(H)) and help to calculate the magnetic entropy change (- Delta S-M) values, and to find the nature of magnetic phase transition. Maximum magnetic entropy change (Delta S-M(max)) values are found as 2.81, 2.76, 2.99, 3.44, 2.77, and 2.14 Jkg(-1) K-1 under 5 T magnetic field change for x = 0.0, 0.6, 0.7, 0.8, 0.9, 1.0 samples, respectively. Arrott plots created from the isothermal magnetization curves show that all samples have a second-order magnetic phase transition. Relative cooling power values are determined as 103.41, 264.96, 341.19, 278.36, 224.13, and 164.42 Jkg(-1) for x = 0.0, 0.6, 0.7, 0.8, 0.9, 1.0 samples, respectively.
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    Structural, Magnetic, and Magnetocaloric Properties of Pb-Substituted La0.7(Te1-xPbx)0.3MnO3 (0.0 ? x ? 0.3) Manganites
    (Springer, 2020) Kılıç Cetin, Selda; Akca, Gonul; Ayas, Ali Osman; Akyol, Mustafa; Ekicibil, Ahmet
    The influence of lead substitution on the magnetocaloric properties of La-0.7(Te1-xPbx)(0.3)MnO3 (0.0 <= x <= 0.3) manganites synthesized by solid-state reaction process was studied both by experimental and theoretical modeling. The X-ray diffraction patterns reveal that samples crystallize in the rhombohedral perovskite structure. Thermomagnetic measurements indicate that the magnetic transition temperature increases gradually from 238 to 262 K with increasing Pb amount in the structure. Maximum magnetic entropy changes (Delta S-M) are determined to be 7.16 for x = 0.0 and 4.76 J kg(-1) K-1 for x = 0.3. Relative cooling power (RCP) values of samples are ranging between 266.94 and 195.21 J kg(-1) at Delta H = 5 T. Due to relatively high Delta S-M and RCP values of the samples, they can be potential materials in magnetic refrigeration applications which work around room temperature.