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    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.
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    Öğe
    Investigation of structural, magnetic and microwave absorption properties of NixCo1-xFe2O4/Ni:ZnO (x:0.0, 0.5, and 1.0) embedded epoxy composites
    (Springer Heidelberg, 2022) Kivrak, Burak; Tumen, Kutluhan Utku; Karaaslan, Muharrem; Akyol, Mustafa
    In this study, NixCo1-xFe2O4/Ni:ZnO (x:0.0, 0.5, and 1.0) epoxy-based composite structures were manufactured by sol-gel method. The structural, morphological and magnetic characteristics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). Electromagnetic wave (EMW) absorption measurements were carried out using a vector network analyzer (VNA) between 8 and 12 GHz (X band). Ni substitution with Co decreases the crystallite size, average particle size, magnetic saturation (M-s) and the coercive field (H-c) values of cobalt-ferrite spinel structure. EMW characterization results showed that minimum reflection loss (RL) - 30.91 dB (99.9% absorption) at 10.76 GHz, and the maximum bandwidth of 1.81 GHz were observed for the RAM1 composite. In addition, the substitution of Ni2+ into the cobalt-ferrite structure resulted in the shifting absorption peaks to the higher frequency region (towards K-u band).
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    Öğe
    Room-temperature magnetocaloric effect in Fe-substituted CoCr2O4 spinels
    (Springer Heidelberg, 2021) Gulkesen, Semiramis; Tumen, Kutluhan Utku; Akyol, Mustafa; Ekicibil, Ahmet
    In this study, structural, magnetic and magnetocaloric properties of Co(Cr1-xFex)(2)O-4 (x=0.0, 0.25, 0.50, 0.75 and 1.0) cubic spinel compounds produced by solgel method were investigated. The cubic crystal structure of CoCr2O4 has not disrupted by Fe substitution, but the lattice parameter increases with increasing Fe content due to bigger ionic radii of Fe3+ ions than Cr3+ ions. The magnetic transition temperature of CoCr2O4 (96 K) is increased to 312 K when 50% Fe is substituted with Cr in CoCr2O4 structure. The maximum magnetic entropy change values are-0.88 J/kgK,-1.27 J/kgK and-1.39 J/kgK under 7 T magnetic field for x=0.0, 0.25 and 0.5 in Co(Cr1-xFex)(2)O-4, respectively. The relative cooling power values are enhancedx5 when 50% Fe3+ ions are substituted with Cr3+ ions in CoCr2O4. Therefore, the CoFeCrO4 sample might be a potential material for magnetic refrigerant applications due to its considerable high magnetization values, having room-temperature magnetic transition temperature, highest magnetic entropy change and relative cooling power compared to other samples.
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    Öğe
    Structural, magnetic and optical properties of Au/YIG, YIG/Au and Au/YIG/Au multilayer thin film stacks
    (Elsevier, 2020) Akyol, Mustafa; Demiryurek, Nazan; Iloglu, Onur; Tumen, Kutluhan Utku; Karadag, Faruk; Ekicibil, Ahmet
    Y3Fe5O12 shortly named YIG thin film and various form of Au and YIG thin film stacks have been grown on quartz substrate using both spin-coating and sputtering methods. The films are crystallized in cubic phase after heat treatments process that is optimized to avoid cracks on the surface. The thickness of the YIG layer measured by cross-section electron microscope imaging technique are found as about 80 nm for all samples. While the root-mean-square surface roughness of the YIG film is in sub-nanometer scale, it increases up to 2.86 nm by adding Au layer in the film structure. All films exhibit in-plane easy axis and low coercive field at room temperature. But, the saturation magnetization values of films decrease with Au layer. Whereas the optical transmission value is around 80% for YIG samples above 400 nm, it decreases dramatically with Au in the film stacks. The highest absorption coefficient value is found as similar to 20 x 10(4) cm(-1) in Q/Au/YIG structure. This strong absorption might come from the localized surface plasmon polaritons of Au noble metals in YIG structure because it enhances the electronic transition from crystal field splitting. As a result of these measurements, it is seen that the Au layer reduces the magnetization of the films, while increases the absorption rate significantly. Due to considerably low production cost of YIG in this work, it might open to commonly use of them in the magneto-optical devices.