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Absorbing the entire X-band via conductive polymer polyaniline coated Y3Fe5O12/NiFe2O4 hybrid composites
(Springer, 2023) Akyol, Mustafa; Aka, Cemal; Inozu, Onat; Alkurt, Fatih Ozkan; Karaaslan, Muharrem
Conductive polymer coated Y3Fe5O12 (YIG)/NiFe2O4 (NFO) hybrid radar absorbing composites were studied in this work. The magnetic YIG and NFO particles were synthesized by sol-gel method, and then covered with a conductive PANI polymer by in-situ polymerization technique. The structural and magnetic properties of produced particles and hybrid composites were studied by XRD, SEM and VSM measurements. The microwave property of the hybrid composites reinforced in the epoxy matrix was studied in the X-band frequency range. The electromagnetic wave absorbing bandwidth in the X-band increases with the content of YIG in the hybrid composites. A broadband radar absorbing has been observed in EPYN08 and EPYN10 hybrid composites having entire X-band with an absorption criterion of - 10 dB. The maximum reflection loss (RL) value was found as - 35.1 dB at 10.8 GHz frequency in EPYN06 sample. The nanocomposite structures formed by combining magnetic and dielectric materials show better electromagnetic wave absorption properties rather than the each components in the composites. Hence, the experimental results of hybrid composites may be a promising candidate for radar and defense vehicles due to their fully absorbing property in the X-band.
Broadband electromagnetic wave absorbing via PANI coated Fe3O4 decorated MoS2 hybrid nanocomposite
(Elsevier Science Sa, 2023) Aka, Cemal; Akgol, Oguzhan; Karaaslan, Muharrem; Akyol, Mustafa
High performance electromagnetic wave (EMW) absorbing material systems are required for stealth applications and sensitive electronic devices. Absorbing of an incident EMW in a wide band range still has limitations in terms of materials system and engineering. It is required to extend the bandwidth and minimize the reflection from the material system for the next level stealth technologies. In this work, hybrid nanocomposite structures are developed by semiconductor flower-like MoS2 nanosheets, Fe3O4 magnetic nanoparticles and conductive poly aniline. A systematic study is presented by investigation the structural, magnetic, morphological, thermal, electronic and electromagnetic characteristic of hybrid nanocomposites (Fe3O4:MoS2, PANI@Fe3O4, PANI@MoS2 and PANI@Fe3O4:MoS2). EMW absorption characteristics results showed that Fe3O4:MoS2 and PANI@Fe3O4:MoS2 hybrid nanocomposites exhibit excellent EMW absorption characteristics. While the minimum reflection loss (RL) value was found as 54.97 dB at 15.99 GHz for the Fe3O4:MoS2 nanocomposite, the broad bandwidth (7.65 GHz) was observed in PANI@Fe3O4:MoS2 hybrid nanocomposite having 39.96 dB RL. According to the experimental results, a lightweight and high temperature resistance PANI@Fe3O4:MoS2 like hybrid nanocomposite can absorb almost 90% of incident EMW in a wide bandwidth.
Comparing Different Approaches to Form Cobalt Oxide Layer on CoPt Nanoparticles
(Adiyaman University, 2020) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, Ahmet
We have studied the effect of preparation methods, under argon gas and in the air environment, on the cobalt oxide formation of CoPt nanoparticles by the polyol process. The formation of cobalt oxide for both samples was investigated by the x-ray diffraction (XRD) method and cobalt oxide peaks are observed in the air prepared sample. Rietveld refinement analyses revealed that all samples exhibit a chemically distorted cubic crystal structure. The average particle size was determined <8 nm by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) was revealed the chemical compositions with possible oxygen formation in the structure. The blocking temperature is reduced to 28 K in the air prepared sample due to cobalt oxide formation. The hysteresis gap disappeared above the blocking temperature and no saturation is observed up to ±5 T external field due to the system switching from ferromagnetic state to paramagnetic state. Similarly, the coercive field was decreased from 1021 Oe to zero with increasing the temperature from 5 K to 300 K. The formations of the cobalt oxide layer did not interact with CoPt nanoparticles, therefore, the maximum exchange bias was observed about 93 Oe at 5 K. © 2020, Adiyaman University. All rights reserved.
Çözücü ve Isıl İşlem Sürecinin MoS2 İnce Filmlerinin Yapısal Özelliklerine Etkisinin İncelenmesi
(2022) Kıvrak, Burak; Akyol, Mustafa
Son yıllarda, geçiş metali kalkojenleri (GMK) kendilerine özgü fiziksel ve kimyasal özelliklerinden dolayı çokça çalışılan malzeme gruplarından biri olmuştur. GMK’ler, optoelektronik uygulamalarda, hidrojen evrim reaksiyonları, enerji depolama sistemleri, güneş pili uygulamalarında ve radar emici sistemlerde sıkça kullanılmaktadır. Bu çalışmada, farklı çözücüler ve ısıl işlem süreçleri kullanılarak üretilen GMK grubundan olan MoS2 ince filmlerinin yapısal özellikleri araştırılmıştır. İnce filmler sol-gel spin kaplama yöntemi ile üretilmiştir. Filmlerin kristalizasyonu farklı sıcaklık değerlerinde vakum altında tutulan ve azot gazı (N2) akışı sağlanan fırın sisteminde sağlanmıştır. Isıl işlem sıcaklığı ve çözücü kimyasalın etkisi yapısal analiz metotları ile değerlendirilmiştir. Bu kapsamda, X-ışını kırınım metodu (XRD) ve Raman saçınım ve taramalı elektron mikroskop (SEM) metodu filmlerin yapısal analizlerinin yapılmasında kullanılmıştır.
Current-driven magnetization switching under zero field in Pt/Ta(wedge)/CoFeB/MgO multilayers
(Aip Publishing, 2022) Akyol, Mustafa; Yu, Guoqiang; Wong, Kin; Wang, Kang L.
The switching of perpendicularly magnetized ferromagnets via current-induced spin-orbit torques is of great interest because of its potential applications in memory and logic devices. However, the in-plane electric current itself is not enough to switch the magnetization. In addition to the electric current, an in-plane external magnetic field is required for magnetization switching. This limits the usage of such devices in spintronic applications. Here, we work on the current-driven perpendicular magnetization switching in the Pt/Ta(wedge)/CoFeB/MgO multilayer. The structural symmetry is broken in both z-axis and in-plane due to the wedge Ta layer, which results in a field-like spin-orbit torque. The beta( z )value extracted from the slope of the offset field vs current density increases with Ta layer thickness (< 1.0 nm) and then decreases up to z-axis asymmetries that enable the current-driven magnetization switching without the need for a magnetic field. We showed switching of the magnetization with a perpendicular magnetic anisotropy, switching in a wide range of Ta layer in Pt/Ta(wedge)/CoFeB/MgO multilayer. Published under an exclusive license by AIP Publishing.
Detailed investigation of structural and magnetic properties of multiphase binary Pd-Co alloys prepared by modified polyol process
(Elsevier Science Sa, 2021) Kaya, Dogan; Adanur, Idris; Akyol, Mustafa; Karadag, Faruk; Ekicibil, Ahmet
Pd-Co based magnetic alloy nanoparticles were prepared by the modified polyol process and stabilized by polyvinylpyrrolidone (PVP) and 3-aminopropyl-trimethoxysilane (APES) capping agents and further reduction of metal salts with Sodium borohydride (NaBH4) at high temperature to form desired NPs. We have a detailed investigation of the effect of Pd concentration in the Pd-Co alloy NPs on structural and magnetic properties. XRD and Rietveld refinement analyses were confirmed that the multiphase structures of fcc-PdCo, fcc-Co, and hcp-Co phases coexist at low Pd loading samples. Over %50 of Pd loading resulted in a single fcc-PdCo phase with reduced lattice parameter to 4.0079 angstrom and d((111))-space to 2.31 angstrom. TEM and SEM images reveal well dispersed and uniformly distributed NPs with an average particle sizes of below 7 nm. The elemental compositions and the characteristic OH, CH, CO stretching peaks of capping agents were confirmed by EDS and FT-IR spectrums, respectively. M(T) and M(H) curves revealed that there are multi magnetic phase transitions in the Pd-Co structure as a function of Pd loading from superparamagnetic to ferromagnetic phase or back to superparamagnetic phase by reducing the temperature from 300 K to 5 K. We observed that the blocking temperature (T-B) could not be detected due to 5% Pd loading below 300 K, while it reduced up to 55 K at high Pd loading of 62%. The coercive field (H-c) was increased to similar to 1900 Oe for Pd0.62Co0.38 sample due to the smallest particle size as 5.26 nm. The highest amount of Co resulted in maximum saturation magnetization (M-s) up to 65.5 emu/g for 5% Pd concentration. We measured the M-r/M-s ratios were less than 0.5, which is due to the internal stress that results in the uniaxial magnetic anisotropy in the structure. The maximum K-eff and mu(f.u). values were found to be over 12.9 x 10(6) erg/cm(3) and 0.72 mu(B) at 5 K for 5% Pd concentration, respectively. (C) 2021 Elsevier B.V. All rights reserved.
Effect of Ag-doping process into the yttrium iron garnet (Y3Fe5O12) thin films on the structural, magnetic and optical properties
(Springer, 2024) Demiryurek, Nazan; Akyol, Mustafa; Karadag, Faruk; Ekicibil, Ahmet
In this work, the effect of Ag doping process (directly and as a nanoparticle) into the Y3Fe5O12 (YIG) thin films on the structural, morphological, optical and magnetic properties was studied in detail. Ag-doped YIG thin films were grown on thermally oxidized Si substrates by following sol-gel and spin-coating methods. All films were crystallized without cracks by two-stages heat treatment process. The XRD patterns confirm the formation of YIG peaks, and metallic Ag peaks which settled into the structure without bonding with the YIG components. In both Ag doping processes, the coercive field (H-c) and saturation magnetization (M-s) values of the samples containing 3% Ag are significantly lower than the other samples. The M-s values of 5% Ag doped samples were found the highest in both series. The M-s values of the films between in-plane and out-of-plane measurement increased with the Ag concentration. The optical measurements indicate an absorption peak in the range of 0-4 eV in both sample series and the optical band gap of the films decreased with the Ag doping due to its metallic characteristic. The ferromagnetic resonance measurements indicate that the lowest FMR linewidth as 92 Oe is seen in the 1% Ag-doped YIG sample. The relatively cheap and easy production of the used method and additive material may enable the widespread the usage of Ag-doped YIG thin films in magneto-optical devices.
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.
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.
Effect of Eu Doping on the Structural, Magnetic and Magnetocaloric Properties in La0.85Ag0.15MnO3
(2018) Akyol, Mustafa
In this research, the effect of Eu doping on the structural, magnetic and magnetocaloric properties inLa0.85Ag0.15MnO3 sample synthesized by sol-gel technique has been studied. The structural analysis showthat crystal structure of the sample is found as rhombohedral being the same as undoped sample. But, theaverage particle size decreases when Eu is doped in the main structure. In the magnetic analysis, amagnetic transition is observed from ferromagnetic to paramagnetic phase around 192 K. The maximummagnetic entropy change (??SM)max and relative cooling power (RCP) values were found as 2.78 J/kgKand 142.31 J/kg under 5 T field change.
Effect of Gd-doping in Ni/NiO core/shell magnetic nanoparticles (MNPs) on structural, magnetic, and hydrogen evolution reaction
(Aip Publishing, 2022) Adanur, Idris; Karazehir, Tolga; Dogru Mert, Basak; Akyol, Mustafa; Ekicibil, Ahmet
In this study, Gd-x-doped Ni/NiO MNPs (x: 0.0%, 2.5%, 5.0%, and 10.0%) with a protective polyvinylpyrrolidone (PVP) layer have been synthesized via a polyol reduction process. The x-ray diffraction patterns revealed that samples have a cubic structure with Fm3m space group and no change in the crystallite structure was observed with doping Gd3+ ions. The crystallite size (D-c) decreases from 2.70 to 1.27 nm when Gd is doped into Ni/NiO MNPs. Transmission electron microscopy analysis revealed that the Ni/NiO MNPs with Gd(5%) concentration are formed as spherical multicore-like shape core/shell MNPs with a protective PVP layer. The magnetic hysteresis measurements taken at 10 and 300 K show that the saturation magnetization (M-s) decreases with increasing Gd3+ ions in the structure. The highest effective magnetic moment (mu(eff)) was obtained as 10.34 mu(B) in the NG-2 sample. We ascribe that the high mu(eff) value in this sample is due to the increase in d-f exchange interaction between Ni(3d(7)) and Gd(4f(7)) and the contribution of the dipole moment of PVP molecules. The electrochemical measurements showed that the current density values were 0.294 and 0.319 mA/cm(2) at-1.3 V in the absence of Gd (NG-0) and Gd(5%) doped (NG-2) samples, respectively. beta c was 159 and 132 mV/dec for NG-0 and NG-2 samples, respectively. The diminishing of beta c and the charge resistance (Rct) proved that the Gd doped catalyst enhanced the hydrogen evolution activity and the Gd(5%) doped sample exhibited the highest catalyst performance.
Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf¦CoFeB¦MgO structures
(Amer Inst Physics, 2016) Akyol, Mustafa; Jiang, Wanjun; Yu, Guoqiang; Fan, Yabin; Gunes, Mustafa; Ekicibil, Ahmet; Amiri, Pedram Khalili
We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf broken vertical bar CoFeB broken vertical bar MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thickness is increased above similar to 7 nm. Although there might be a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure. Published by AIP Publishing.
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.
Effect of reducing agent and surfactant on the morphology, structural and magnetic properties of Ni magnetic nanoparticles
(Taylor & Francis Ltd, 2018) Adanur, Idris; Akyol, Mustafa; Ekicibil, Ahmet
We report the effect of reducing agent and surfactant on the morphology, structural and magnetic properties of Ni magnetic nanoparticles (MNPs) synthesised by the polyol process. The samples in this work were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The XRD results indicate that samples synthesised by EG-NaOH and 1.2H-OAm/OAc have a cubic structure with space group Fm-m. The average crystallite sizes of these samples are found to be approximate to 20.7 and 16.2nm, respectively. The sample synthesised by a combination of EG-OAm/OAc grows in nanorod form, whereas that synthesised by EG-NaOH and 1.2H-OAm/OAc has a spherical shape. The temperature dependence of the magnetisation, (M-T) measurements, indicate that the EG-NaOH sample has a superparamagnetic transition, while the 1.2H-OAm/OAc sample shows ferromagnetic behaviour in the temperature range of 5-380K. The magnetic anisotropy constants of the EG-NaOH and 1.2H-OAm/OAc samples extracted from the M-T experiments, are 141.3x10(5) and 10.5x10(5)erg/cm(3), respectively. In addition, the magnetic hysteresis measurements taken at 5 and 300K show that the 1.2H-OAm/OAc sample is more stable than the sample synthesised by EG-NaOH. The overall results are important for the use of the Ni MNPs for low- and room-temperature applications in bio- and nano-technology.
Effect of Synthesizing Process on the Formation of Fe3O4 Magnetic Nanoparticles
(2023) Aka, Cemal; Akyol, Mustafa
In this work, the effect of synthesizing process on the morphology, structure, and magnetic properties of Fe3O4 magnetic nanoparticles have been studied by performing X-ray diffraction, scanning electronic microscopy, and vibrating sample magnetometer measurements. Fe3O4 nanoparticles were synthesized by hydrothermal and solvothermal methods. X-ray diffraction analysis revealed that both samples have cubic crystal phase. However, Fe2O3 impurity peaks were observed in the sample synthesized by hydrothermal method. The crystallite sizes of samples synthesized by hydrothermal and solvothermal methods were approximately 38 and 24 nm, respectively. The scanning electron microscope images show that spherical porous and cubic shape Fe3O4 nanoparticles were obtained by solvothermal and hydrothermal method, respectively. The average particle sizes of Fe3O4 samples synthesized by hydrothermal and solvothermal methods were determined as 220 and 450 nm, respectively. Both samples behave a soft ferromagnetic characteristic having almost zero coercive field. The magnetic saturation values of Fe3O4 nanoparticles synthesized by hydrothermal and solvothermal methods were determined as 28.78 and 77.31 emu/g, respectively. As a result of the characterizations, porous Fe3O4 nanoparticles synthesized by solvothermal method show better crystal structure, morphological and magnetic properties than Fe3O4 nanoparticles synthesized by hydrothermal method.
Effect of Ta insertion between Pt and CoFeB on interfacial magnetic anisotropy in Pt/CoFeB/MgO multilayer thin-film stack
(Springer, 2020) Akyol, Mustafa; Kivrak, Burak; Tumen, Kutluhan Utku; Ekicibil, Ahmet
The effect of a thin Ta layer inserted between Pt and CoFeB layers on perpendicular magnetic anisotropy (PMA) with MgO barrier layer has been studied. The crystallinity was studied by performing high-resolution x-ray diffraction (HR-XRD) technique. While the crystal peak of Pt is observed in all sample stack that is oriented as (111) face-centered cubic crystal structure, a very weak and broad alpha-Ta (110) peak is observed when Ta layer thickness is above 0.8 nm. Magneto-optical Kerr effect (MOKE) measurements show that the PMA could be enhanced by inserting Ta layer between Pt and CoFeB layer. The magnetically dead layer thickness (t(dead)) and the interfacial anisotropy energy density (K-i) of the various Ta-inserted layer thickness were found as 0.135 nm; 0.75 erg/cm(2), 0.141 nm; 1.02 erg/cm(2), 0.187 nm; 1.15 erg/cm(2), for t(Ta) = 0.0, 0.5, and 1.0 nm, respectively. Both t(dead) and K-i increase with Ta-inserted layer thickness in Pt/Ta(t)/CoFeB/MgO multilayer film stack. The sources of interfacial magnetic anisotropy can be hybridization, crystallinity properties, and/or B/Ta diffusion effect at the interfaces in Pt/Ta(t)/CoFeB/MgO multilayer film stack.
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).
Electromagnetic wave absorption in polyaniline coated Y3Fe5O12/Carbon-Black hybrid composites
(Elsevier Science Sa, 2024) Akyol, Mustafa; Altay, Melek; Parajuli, Saroj; Teksen, Fikret Alpay; Karaaslan, Muharrem
Y3Fe5O12(YIG)(1-x)/Carbon-Black(CB)(x) (0.00 <= x <= 1.00; 0.25 steps) coated with polyaniline (PANI), forming a core-shell structure, were synthesized by in-situ polymerization following sol-gel and solid-state reactions. The crystalline, surface morphology and magnetic properties of YIG(1-x)/CBx and PANI@YIG(1-x)/CBx hybrid composites were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM), respectively. Electromagnetic wave (EMW) absorbing properties were investigated by measuring dielectric parameters in the 2-18 GHz frequency range. The reflection loss (RL), impedance matching, and loss tangent were studied in detail. The electromagnetic wave absorbing mechanisms were discussed by considering dielectric and magnetic losses, as well as microstructural properties of the samples. The EMW absorbing performance of the YIG(1-x)/CBx composites showed a broadband absorption property (7.0 GHz bandwidth at -10 dB reflection loss value) in YIG(0.75)/CB0.25 composite. When the composites are covered with conductive PANI, the EMW absorbing performance is enhanced in terms of RL (minimum -36.5 dB) and effective absorption bandwidth (EAB) (maximum 10.2 GHz at -10 dB) values due to increasing scattering probability, interfacial polarization and conduction loss of the penetrated EMW. The results showed that a wider absorption frequency range could be obtained by coating PANI on YIG/CB composite.
Electronic and magnetic properties of boron substituted CuFeO2 delafossite oxide
(Taylor & Francis Ltd, 2024) Ezircan, Ali; Aslan, M. Selim; Miyazaki, Hidetoshi; Akyol, Mustafa; Ozkendir, O. Murat; Ekicibil, Ahmet; Ozturk, Hakan
Synchrotron x-ray diffraction (SR-XRD) and X-ray absorption fine structure spectroscopy (XAFS) were used to investigate the crystal and electronic properties of boron-substituted CuFeO2 material at room temperature. Without boron substitution, the polycrystalline structures of the trigonal (rhombohedral) Rm' over bar m' CuFeO2 (87.7%) and hexagonal 'P63/mmc' (12.3%), which were also present in each sample but in different proportions, were utilised to identify the base material. XRD patterns revealed that, beyond 10% boron substitution, the metal-oxygen bonds (Fe-O and Cu-O) weakened, resulting in the formation of new tetragonal 'I41/amd' CuFe2O4 crystals. Although the CuFeO2 structure was preserved, it is conceivable that the presence of other crystal structures could lead to the formation of new features. This state arose as a result of CuFe2O4 crystallization and the impact of boron activity on the surrounding oxygen structures. By measuring magnetisation at both swept temperatures (10-300 K) and applied magnetic fields (+/- 30 kOe), the magnetic properties of the samples were investigated. In the 10-300 K temperature range, the polycrystalline samples exhibit a ferromagnetic property without a magnetic phase transition. This suggests that replacing B with Fe in CuFe(1-x)BxO(2 )does not influence the primary magnetic property of CuFeO2. The samples' saturation magnetisation (Ms) values gradually fall as the B substitution content increases with Fe. This is because there's a chance that the non-transition metal B in CuFe1-xBxO(2) will boost antiferromagnetic superexchange Cu-O interactions while lowering the p-d exchange interaction.
Evaluation of nanoparticle formation and magnetic properties by boron doping in Ni/NiO? nanoparticles
(Springer, 2020) Adanur, Idris; Akyol, Mustafa; Tezcan, Fatih; Kardas, Gulfeza; Ekicibil, Ahmet
In this work, Boron-doped B-x:Ni/NiO delta [x(%) = 0.0, 5.0, 10.0 and 15.0] core/shell magnetic nanoparticles were synthesized by the polyol reduction process. The XRD spectra of the samples indicate that the B addition does not cause any change in the cubic structure of Ni. The TEM photographs present that nanoparticle formation and accumulation orientation occurs in various shapes as spherical, octahedral-like and octopus-like accumulation. The average particle sizes of B-x:Ni/NiO(delta)MNPs forx(%) = 0.0, 5.0, 10.0, 15.0 were found as similar to 90, 12, 46, 5 nm, respectively, from the TEM images. It is observed from the temperature and magnetic field dependence magnetization measurements that magnetization of Ni/NiO delta core/shell MNPs increases with increasing Boron concentration from 5 to 15%. One can be deduced that this increment in the magnetization comes from the resulting of strengthening the Ni-B ferromagnetic interaction. The highest saturation magnetizations under 1 T magnetic field were found as similar to 37 and similar to 30 emu/g at 10 and 300 K, respectively.

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