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We mainly focused on synthesis of boron doped cobalt gallium oxide (B doped CoGa2O4) nanoparticles. In the study, varied amount of B doped CoGa2O4 nanopowders were produced employing Sol-Gel technique. The structural characterizations of the particles were performed using x-ray powder diffractometer (XRD) and x-ray photoelectron spectroscopy (XPS) measurements. Rietveld refinements were utilized to investigate B atom replacement and thus, the changes in lattice parameters. Furthermore, the reflectance and absorbance performances were measured by UV–visible spectrophotometer in order to determine electronic energy level configurations through the band gap. The relationship between crystal structural and formation of electronic energy levels was also investigated according to the locations of substituted B atoms.

In this work, the irreversible effects of an applied electric field on the magnetotransport properties of LaAlO3/SrTiO3 conducting interfaces are investigated, with focus on their multiband character. Samples of different types, namely with either crystalline or amorphous LaAlO3 overlayer, are studied. The two-band analysis highlights the similarity of the electronic properties of crystalline and amorphous interfaces, regardless much different carrier densities and mobilities. Furthermore, filling and depletion of the two bands follow very similar patterns, at least in qualitative terms, in the two types of samples. In agreement with previous works on crystalline interfaces, it is observed that an irreversible charge depletion takes place after application of a first positive back gate voltage step. Such charge depletion affects much more, in relative terms, the higher and three-dimensional dyz, dzx bands than the lower and bidimensional dxy, driving the system through the Lifshitz transition from two-band to single band behavior. The quantitative analysis of experimental data evidences the roles of disorder, apparent in the depletion regime, and temperature. Noteworthy, filling and depletion of the two bands follow very similar patterns in crystalline and amorphous samples, at least in qualitative terms, regardless much different carrier densities and mobilities.

This chapter discusses the emergence conditions of energy states arisen from the interaction of electromagnetic waves with an optically active planar slab covered by graphene sheets. All energy configurations inside and outside the graphene layers are explicitly revealed. In particular, we specialize to some certain cases of maximal energy storage by imposing the spectral singularity condition and show that energy density stored within graphene layers can be increased tremendously because of the presence of graphene layers surrounding the complex potential slab. Method presented here relies on the most fundamental principles embracing its power from Maxwell’s equations and employing the whole control of transfer matrix formalism of scattering theory. In this respect, various situations are discussed to see how graphene sheets can be handled in order to increase the energy storage within a slab. It is attained that both graphene layers are required and there must be currents flowing in the same direction in order to preserve the parity invariance. If the parity invariance is broken, energy stored inside the slab slumps to much lower values. Besides, it is illustrated that graphene features can be effectively used in order to enhance energy storage efficiently. Predictions proposed in this work are perceptibly supported by the corresponding graphical demonstrations. The suggested method is quite illustrative and instructive and gives rise to extend all other cases by following similar steps. These observations and predictions suggest a concrete and sound way of forming graphene-related energy storage devices.

The study was based on understanding the relationship between titanium (Ti) doping amount and magnetic heating performance of magnetite (Fe3O4). Superparamagnetic nanosized Ti-doped magnetite ((Fe1−x,Tix)3O4; x = 0.02, 0.03 and 0.05) particles were synthesized by sol-gel technique. In addition to (Fe1−x,Tix)3O4 nanoparticles, SiO2 coated (Fe1−x,Tix)3O4 nanoparticles were produced as core-shell structures to understand the effects of silica coating on the magnetic properties of nanoparticles. Moreover, the magnetic properties were associated with the Néel relaxation mechanism due to the magnetic heating ability of single-domain state nanoparticles. In terms of results, it was observed that the induced RF magnetic field for SiO2 coated (Fe0.97,Ti0.03)3O4 nanoparticles caused an increase in temperature difference (ΔT), which reached up to 22 °C in 10 min. The ΔT values of SiO2 coated (Fe0.97,Ti0.03)3O4 nanoparticles were very close to the values of uncoated Fe3O4 nanoparticles.

The study was focused on optimizing the procedure of synthesizing iron gallate (FeGa2O4) nanoparticles by mechanochemical techniques. Due to a lack of information in the literature about the sequence of synthesis procedures of FeGa2O4 structures, the study is based on the establishment of a recipe for FeGa2O4 synthesis using mechanochemical techniques. Rotation speed, grinding media, and milling durations were the optimized parameters. At the end of each step, the structure of the resulting samples was investigated using the X-ray diffraction (XRD) patterns of samples. At the end of the processes, the XRD patterns of the samples milled under an air atmosphere were coherent with the XRD pattern of the FeGa2O4 structure. XRD patterns were analyzed employing Rietveld refinements to determine lattice parameters under the assumption of an inverse spinel crystal formation. Furthermore, a fluctuation at band gap values in the range of 2.39 to 2.55 eV was realized and associated with the excess Fe atoms in the lattice, which settled as defects in the crystal structures.

We investigated the effect of Co atoms, doped into ZnO lattice, on ionic conductivity in the internal grains or through the grain boundaries. Influence of Co amount on the conductivity was associated with enhanced activation energies of the ionic conductivity through the grain boundaries. The change in activation energy implies that the mechanism of ionic conduction through the boundaries can be modified by the Co amount in the lattice. Three conductance mechanisms were identified by the Cole-Cole plots in order to understand the relaxation mechanism and activation energies of ionic transportations. Newly formed activation energy, 395 meV, by increasing Co amount up to 10 mol% was attributed to the ionic conductivity through the enhanced (or increased) (Zn,Co)O/ZnO) interface at the grain boundaries. In addition, the activation energy was also enhanced by the electronic stability at high temperatures due to decrease in electronic conductivity in the Co-doped ZnO compared to that in undoped ZnO.

The recent studies indicate that internal point defects in solid electrolytes modify the electronic and ionic conductivity and relaxation mechanism of solid oxide fuel cells. We focused on synthesis of Lithium (Li) doped Zn1-xCoxO (x = 0.00, and 0.10) nanoparticles employing chemical synthesis technique with a reflux setup under constant Argon gas flow. The structural characterizations were performed by x-ray powder diffractometer (XRD) and x-ray photoelectron spectroscopy (XPS). Then, Rietveld refinements were performed to investigate the replacement of Li atom amount in ZnO lattice. Moreover, the variations in ionic conduction dependent on 5, 10 and 20 mol% Li doped ZnO were analysed via ac impedance spectroscopy. The complex measurements were performed in an intermediate temperature range from 100 °C to 400 °C. Ac conductivity responses of each sample were disappeared at a certain temperature due to becoming electronic conductive oxides. However, this specific temperature was tuned to high temperature by Li doping amount in ZnO lattice. Furthermore, the activation energy change by Li dopant amount implied the tuneable ionic conduction mechanism.

The study was focused on to synthesis of pure and fluorine-doped SnO2 (FTO) nanoparticles by sol-gel method combining with low temperature, 300 °C, annealing process, immediately after gelation. The relationship between the structural and optical properties of FTO was investigated to understand the effects of fluorine amount on the optical transmittance ratio and configuration of electronic energy levels. Homogeneous distribution of fluorine in SnO2 lattice was observed at all synthesized FTO powders. In addition, the change in electronic energy configuration was investigated by the fluctuation from 3.85 eV to 3.64 eV in band gap energy values according to the amount of fluorine in SnO2. The optical transmittance values were observed in the range of ∼90% and 95%. Optical analysis proved that the amount of fluorine had no specific effect on the high optical transmittance performances of SnO2 particles in the visible region, however the F amount had high impact on band gap energy values due to due to varying defect intensity.

We measured the absorption/transmission performance of ZnO thin films doped with europium (Eu) and aluminum (Al). ZnO and Zn1−(y+0.01)(Al0.01, Euy)O (y = 0.00, 0.01, 0.03 and 0.05) nano particles were synthesized using sol–gel method and covered on a soda-lime glass surface by spin coating. After annealing at 500 °C, UV–Vis. measurements were performed in wavelength range of 300 and 800 nm to calculate the band gap of nano particles from the absorption/transmission performances. The resistivity measurements were employed to understand the relationship between band gap and DC electrical performance by Eu amount of each Zn1−(y+0.01)(Al0.01, Eu y )O thin film. As a conclusion, after reaching a minimum value with 1 mol% Eu doping, a monotonic increase in band gap was observed by enhancing Eu amounts in Zn0.99Al0.01O lattice.

We investigated magneto-electrical properties and the effect of intrinsic point defects in the lattice on film properties of 10 mol% cobalt containing ZnO thin films that were doped with 0.7 ± 0.1 to 1.1 ± 0.2 mol% W atoms. Thin films were deposited on Si (100) substrates. The anomalous Hall Effect seen in magneto-electrical measurements indicated a correlation between the polarized spins and the positive magneto-resistivity due to hole and electron mediated interactions. N-type carriers were dominant in conductivity, as shown by Hall resistance measurements. The 55 % positive magneto-resistivity and the split of 132.3 ± 0.1 Ω and 28.5 ± 0.1 Ω differences in the magneto-hysteresis curves through both negative and positive regions, respectively, proved that a polarized spin current was effectively formed under both s-d and p-d interactions. In addition, the shallow energy levels, close to extreme points of conduction and valance bands, reinforced the polarized spin current.

The magnetic nature in Co and W doped ZnO lattice, which included specific concentration of defects, is investigated by magneto electrical measurements. The results are reported based upon the findings of longitudinal and transverse magneto electrical transport changes at 2 K. The transverse magneto electrical transport analyses are carried out with the scanning speeds of 20 Oe/s, 50 Oe/s, 100 Oe/s and 190 Oe/s in order to understand the relaxation of polarized spins. In the highest scan speed of 190 Oe/s, the relation between the polarized spins and positive magneto resistivity is revealed through both hole and electron mediated interactions. Although Hall resistance measurements show the dominant carriers as n-type, the 10±1% positive magneto resistivity and a split of about 3.1±0.2 Ohm in magneto hysteresis curve prove that a polarized spin current is formed under both s–d and p–d interactions effectively.

We investigated the electrical properties of ZnGa 2 O 4 via AC (alternating current) Impedance Spectroscopy method comparing with ZnO reference material. Experimentally, AC electrical conductivity of ZnO and ZnGa 2 O 4 were found to be a function of temperature and grain size; i.e., the increase in grain size of the ZnO led a decrease in room temperature conductivity from 1.35 × 10 −7 S cm −1 to 9.9 × 10 −8 S cm −1 . The temperature dependent resistivity variation of ZnGa 2 O 4 and ZnO were similar to each other with varied responding temperature. Likewise, the conductivity for ZnGa 2 O 4 decrease from 2.2 × 10 −8 S cm −1 to 3.8 × 10 −9 S cm −1 upon an increase in grain size from ∼0.5 μm to 100 μm, accordingly. In addition, a rise in temperature caused an increase in conductivity and led to a corresponding shift in the relaxation time towards the lower values. The semicircles in Nyquist plots disappeared at temperature above 250 °C and 700 °C for ZnO and ZnGa 2 O 4 , respectively. The AC measurements were also correlated with the size dependent activation energies (171 meV for 0.5 μm ZnO and 1200 meV for 0.5 μm ZnGa 2 O 4 ).

This article investigates the effects of intrinsic point defects and extrinsic W atoms on magneto electrical properties in the ZnO lattice. The analyses were accomplished for ∼0.5% W including ZnO thin films, grown using a radio frequency (RF) magnetron sputtering system. The polarized spin current dependent magnetic formation was investigated by longitudinal and transverse magneto electrical measurements in a temperature range of 5 K to 300 K. The positive magneto resistivity (PMR) ratios reached 28.8%, 12.7%, and 17.6% at 5 K for thin films, having different post-deposition annealing conditions as a consequence of ionic W dependent defects in the lattice. Furthermore, an anomalous Hall effect, originating from polarized spin currents, was understood from the split in Hall resistance versus magnetic field ( R xy ( H )) curves for the thin film with high amount of Zn 2+ and W 6+ ionic defects.

The present study describes magnetic interactions in (Zn1-xCox)Ga2O4 (x = 0.05, 0.10, and 0.20) particles dependant on Co atoms in both tetrahedral and octahedral sites. The effects of substituted Co atoms to magnetic character are analyzed using Curie-Weiss law. The ferromagnetic character is found dominant in (Zn1-xCox)Ga2O4 semiconductors for x values lower than 0.10; in addition, a specific hysteresis with 139 ± 50 Oe coercivity is observed for 5% Co-doped ZnGa2O4. The high Co amount in tetrahedral site increased the number of antiferromagnetic couplings and the hysteresis at 300 K disappeared for (Zn0.80Co0.20)Ga2O4 particles. Furthermore, the Co+3 ions in the octahedral site decreased µeff values, per Co amounts, in the range of 4.89 ± 0.01 µB/Co to 4.44 ± 0.02 µB/Co, because of enhancing paramagnetic behaviors.

We employed solid state reaction technique to synthesize ZnGa 2 O 4 particles, produced in steps of mixing/milling the ingredients in H 2 O following thermal treating under 1200 °C. We compare spinel and partially inverse spinel structure in ZnGa 2 O 4 particles using Rietveld refinement. Crystal structure of ZnGa 2 O 4 particles was identified with two structural phases; normal spinel structure and partially inverse spinel structure using Rietveld refinement. It is found that the partially inverse spinel structures occupy nearly 13% and the rest is normal spinel structure. The obtained X-ray diffraction data show that lattice constant and the position of Oxygen atoms remain almost constant in both structures. The characterization of the particles was also improved using X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy measurements. The optical analyses were done with UV–visible spectroscopy. The band gap, calculated from climate point of UV–visible data, was found as 4.6 ± 0.1 eV. Despite no unexpected compound (such as ZnO and Ga 2 O 3 ) in the structure, the optical analyses were shown defective ZnO structure in ZnGa 2 O 4 .

We analyze the effect of postdeposition annealing conditions on both the structure and the created defects in Zn0.90Co0.10O thin films, which deposited on the Si(100) substrates by the radio frequency magnetron sputtering technique using a homemade target. The dependence of the number and distribution of defects in homogeneously substituted Co+2 for Zn+2 ions in ZnO lattice on the annealing conditions is investigated. Orientations of thin films are in the [0002] direction with a surface roughness changing from 67 ± 2 nm to 25.8 ± 0.6 nm by annealing. The Co+2 ion substitution, changing from 7.5% ± 0.3% to 8.8 ± 0.3%, leads to the formation of Zn–O–Co bonds instead of Zn–O–Zn bonds and splitting of the Co 2p energy level to Co 2p1/2 and Co 2p3/2 with an energy difference of 15.67 ± 0.06 eV. The defects in the lattice are revealed from the correlations between Zn–O–Co bonds and intensity of the Raman peak at around 691 cm−1. In addition, the asymmetry changes of O 1s peak positions in the x-ray photoelectron spectra are in agreement with the Raman results.

We investigated intra/inter particle interactions in single domain size magnetite (Fe3O4), maghemite (gamma-Fe2O3) and hematite (alpha-Fe2O3) iron oxide particles. The magnetic analyses were done using vibrating sample magnetometer and magnetic resonance measurements that were taken from 5 to 300 K and from 120 to 300 K, respectively. The magnetic resonance analyses were done for the iron oxides, frozen under 5000 G fields in glycerol matrix. By changing the temperature, a change in resonance field lines was observed at each Fe3O4, gamma-Fe2O3 and alpha-Fe2O3 nanoparticles. However, the fits in resonant lines showed that Lande g values (spectroscopic splitting factor) stayed stable with temperature decrease. The thermal sensitivities that were determined from Lande g factors, revealed three dominant interactions on resonant lines namely; the exchange coupling in between Fe2+, Fe3+ and O (g(1) = 3.01 +/- 0.08), Fe3+ centers (1.88 +/- 0.03

Magnetic properties, arising from surface exchange and interparticle interactions of the Fe3O4 (magnetite) nanoparticles, were investigated in the temperature range of 5–300 and 120–300 K using vibrating sample magnetometer technique and electron spin resonance spectroscopy, respectively. The research was based on to figure out the origin of intraparticle interactions and the change of interparticle interactions in wide size range Fe3O4 nanoparticles. The analyses were done for samples having almost same particle size distributions. The average particle sizes were changed in between 30 ± 2 and 34 ± 2 nm. The observed magnetization values were demonstrated the mixture of single-domain size particles, exhibiting both single-domain (SD) and superparamagnetic (SPM) states. The symmetry of resonance curves changed according to the ratio of SD and SPM-stated particles in mixture under located temperature. The changes of anisotropy up to domain state were understood by freezing magnetic moment in glycerol matrix from room temperature to 120 K under 5-kG field. The shift of H R values to higher magnetic fields and the more symmetric resonance spectrum proved the effect of anisotropy and interparticle interactions fields on magnetic behave. In addition, the origin of intra-interaction was exposed from Fe3+ centers and exchange coupling in between Fe2+, Fe3+, and O−, and Fe3+ centers found from g factor (g).

The interparticle magnetic interactions of hematite (α-Fe 2 O 3 ) nanoparticles were investigated by temperature and magnetic field dependent magnetization curves. The synthesis were done in two steps; milling metallic iron (Fe) powders in pure water (H 2 O), known as mechanical milling technique, and annealing at 600 °C. The crystal and molecular structure of prepared samples were determined by X-ray powder diffraction (XRD) spectra and Fourier transform infrared (FTIR) spectra results. The average particle sizes and the size distributions were figured out using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The magnetic behaviors of α-Fe 2 O 3 nanoparticles were analyzed with a vibrating sample magnetometer (VSM). As a result of the analysis, it was observed that the prepared α-Fe 2 O 3 nanoparticles did not perform a sharp Morin transition (the characteristic transition of α-Fe 2 O 3 ) due to lack of unique particle size distribution. However, the transition can be observed in the wide temperature range as “a continuously transition”. Additionally, the effect of interparticle interaction on magnetic behavior was determined from the magnetization versus applied field ( σ ( M )) curves for 26±2 nm particles, dispersed in sodium oxalate matrix under ratios of 200:1, 300:1, 500:1 and 1000:1. The interparticle interaction fields, recorded at 5 K to avoid the thermal interactions, were found as ∼1082 Oe for 26±2 nm particles.

The outline of magnetic interactions in DMSs was determined using Zn1−x Co x O particles, where “x” was changed as 0.01, 0.05, 0.10, 0.15, and 0.20. The syntheses were accomplished though mechanical milling and thermal treatment, known as solid state reaction. The formation of each synthesis was monitored by differential thermal and thermo gravimetric methods (DT-TGA). Substitution of Co2+ ions with Zn2+ host atoms in a ZnO lattice was analyzed using X-ray diffraction (XRD) patterns, Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray spectrometry (EDS) data, transmission electron microscopy (TEM) figures, scanning area electron diffraction (SAED) patterns, and X-ray photo spectroscopy (XPS) spectrum. The measured Co contents in ZnO lattice were found to be ~0.7% less than the expected result. In addition to Zn1−x Co x O particles, tungsten (W) contaminations were noticed in the variations of 1.5 ± 0.2%, as originating from the abrasion between the miller and balls. The progressive replacement of Co2+ with Zn2+ host ions in ZnO lattice from 1% to 20% decreased the band edge from 3.03 ± 0.01 eV to 2.95 ± 0.01 eV, respectively. Co doping has also changed the magnetic nature of the ZnO. Although having both interactions (ferromagnetic and antiferromagnetic), dominance of ferromagnetic behavior was only observed for Zn0.99Co0.01O with the coercivity of ~154 ± 50 Oe and positive Curie–Weiss temperature as 79 ± 1 K. However, the calculated $$ {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} $$ values have proved that the higher Co2+ concentrations in ZnO lattice have increased the efficiency of antiferromagnetic interactions. Surprisingly, there was no rapid change at $$ {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} $$ values as mentioned in previous works.

In this study, nanosize magnetite (Fe3O4) particles have been prepared directly from metallic iron (Fe) powder within distilled water (H2O) by using a planetary ball mill, and the effect of milling time has been investigated. According to Rietveld refinement result obtained from X-ray diffraction (XRD) analyses, the amount of Fe decreases from 98.2% to 0.0%, and it is transformed into Fe3O4, from 1.8% to 100.0%, with the increasing milling time from 1 to 48 h. Due to similar crystal structure of the magnetite and maghemite (gamma-Fe2O3), FTIR and Raman spectroscopies as well as a chemical analysis method was used to verify the magnetite structure. FTIR spectra have clearly revealed absorption peaks around 628, 581 and 443 cm(-1), which are in good agreement with the characteristic absorption peaks of Fe3O4. In addition Raman analysis verified the formation of magnetite phase with a clear main band peak at 671 cm-1. Chemical analyses have shown that the total amount of Fe in the milled sample for 48 h is 73.04%, which contains 24.10% Fe2+ and 49.34% Fe3+. These results are consistent with the theoretically estimated values of the magnetite. It has been observed that the saturation magnetization decreased from 146.02 to 63.68 emu/g with increasing milling time due to the formation of the ferrimagnetic magnetite phase. (C) 2010 Elsevier B.V. All rights reserved.

Both ZnO and Zn0.99Co0.01O semiconductors were synthesized through solid state reaction via mechanical milling and thermal treatment. Initially the wurtzite ZnO structures of the synthesized particles were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Since these techniques were unable to identify both contamination atoms and Co distribution, energy dispersive X-ray spectrometry (EDS) was used. EDS showed a successful doping of Co atoms with the atomic ratio of 0.9 ± 0.1%, and also showed a contamination of tungsten (W) atoms, in the atomic ratio of 1.6 ± 0.2% for Zn0.99Co0.01O, and 1.3 ± 0.2% for ZnO. Substitutions of Co+2 ions with Zn+2 host atoms in the ZnO lattice were exposed through X-ray photo spectroscopy (XPS) data of Co 2p electronic energy levels. UV-vis absorption spectroscopy (UV-vis) was also used to prove Co substitutions in the ZnO lattice. This was revealed by a decrease in band gap from 3.25 ± 0.01 eV to 3.03 ± 0.01 eV, and the existence of newly permitted transitions between intra ionic d-d* levels. The ferromagnetic effect of Co doping in ZnO lattice was revealed by the coercivity of ~154±50 Oe and positive Curie-Weiss temperature, 79 ± 1 K. Beside ferromagnetic interactions, the calculated effective Bohr Magnetron (?eff), 0.32±0.01 ?B, suggested anti-ferromagnetic interactions due to be less than the theoretical spin based magnetic moment of Co2+ ions, 3.0 ?B.

Effects of various Cr and B sources and preheating con- ditions on the high temperature synthesis of chromium orthoborate were studied. Precursors were mixed, ground, heated at 1000 °C and reground. The obtained products were checked by XRD, vi- brational and electronic spectroscopy, SEM and density measure- ments. Some characteristic properties were redetermined and com- pared with the earlier data. The reaction between hydrated Cr(III) sulfate and boric acid (or hydrated ammonium borate salts) was

In this work, we describe the effect of milling speed on the formation, crystallite size, and lattice parameter of nanocrystalline ZnO in a single step process that is based on wet-milling of metallic Zn in distilled water. The samples were characterized by XRD, TEM, and FTIR spectra. The analyses reveal that although the 150 rpm milled sample exhibits imprints of Zn (OH) 2 , 200, 250, 300, and 350 rpm milled samples possess the standard hexagonal ZnO wurtzite structure. The crystallite size and lattice parameters of the samples were calculated from the XRD patterns by applying the Maud refinement procedure. According to the results, average crystallite size of the ZnO nanocrystals is in the range of 27.3–31.4 nm depending on the milling speed.

We investigated the size dependent magnetic properties and heating mechanism of spinel CoFe2O4 nanoparticles, which synthesized using the nonhydrolytic thermal decomposition method. The size of CoFe2O4 nanoparticles was arranged with the variation of solvent type, reflux time, and reflux temperature. The optimum size range was determined for magnetic fluid hyperthermia. The particles with 9.9 +/- 0.3 nm average diameter have the highest heating ability in the AC magnetic field having 3.2 kA/m amplitude and 571 kHz frequency. The maximum specific absorption rate of 22 W/g was obtained for 9.9 +/- 0.3 nm sized CoFe2O4 nanoparticles. The calculations and experimental results showed the dominancy of Brownian relaxation at the heat production of synthesized 9.9 +/- 0.3 nm nanoparticles. In contrary, the magneto-heating in 5.4 +/- 0.2 nm particles mainly originated from Neel relaxation.

We systematically investigated the effective surface anisotropy of CoFe2O4 nanoparticles dependant on the thickness of SiO2 shell. XRD (X-ray powder diffraction) patterns and TEM (transmission electron microscopy) micrographs were used to investigate the structure of particles and thickness of SiO2 shell, respectively. The thicknesses of SiO2 shell with 5.41 nm on CoFe2O4 nanoparticles were increased up to 14.04 ± 0.05 nm by changing the amount of added TEOS by, 0.10, 0.25, 0.50, 1.00, 1.50, and 2.50 mL. The increase of the SiO2 thickness shell decreased the effective anisotropy due to decline the effectiveness of the dipolar magnetostatic interactions, determined from Vogel–Fulcher equation, between the particles. The declines in the Keff values stabled at around 3.76 ± 0.11 × 105 J/m3 for TEOS amount higher than 1.5 mL.

Zn0.90Co0.10O particles, synthesized by mechanical milling and thermal treatment, were pressed at 25 tons to form a 2” target for a radio frequency (r. f.) magnetron sputtering system. Using this target, thin films were deposited on (0001) oriented sapphire (α-Al2O3) substrates under 30W, 60W and 120W r. f. powers. Structural analyses of these films were done with X-Ray Diffractometer (XRD), Energy Dispersive X-Ray Spectrometry (EDS), X-Ray Photo Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The ZnO films were deposited with (0002) preferred direction, which was coherent to (0001) ordered α-Al2O3. Impurity phases, such as Co clusters, CoO and Co3O4, were not detected with the surface analyses of Zn0.90Co0.10O thin films. Substituted Co atoms in the host ZnO matrix were identified by the binding energy peak of Co2p3/2, 781.3±0.4eV, and the energy difference of ∼15.61±0.03eV between Co2p1/2 and Co2p3/2. These results also proved that there were no Co clusters or Co3O4 phases in the lattice. Homogeneity of Co atoms in the lattice was shown by EDS spectra. It was understood that the higher r. f. power caused the more homogeneous distribution of Co and Zn atoms in thin films. Distributions of Co and Zn on the film surface, deposited under 120W, were found as 8.1±0.1% (normalized atomic ratio) and 91.7±0.7% (normalized atomic ratio), respectively, and the surface roughness of thin film was demonstrated by AFM figures as 14.2±0.1nm.

This study is to understand the effect of oxidation, especially magnetically, on iron nanoparticles. According to generation of the oxidated iron nanoparticles, mechanical alloying technique was used and nanosized magnetite (Fe3O4), maghemite (γ-Fe2O3) and hematite (α-Fe2O3) particles were obtained as the resultant samples. The reactance to the thermal treatment was determined by differential thermal analysis and thermogravimetric (DTA-TG) measurements. X-ray powder diffractions (XRD) helped to exhibit the structure of the sample by ICDD cards and to determine the size of nanoparticles by using the Scherrer formula. On the other hand, VSM (vibrating sample magnetometer) measurements were determined to understand the magnetic behaviour. Through the transformation of Fe3O4 to other iron-oxides, two exothermic peaks were observed at around 169.11 °C and 562.61 °C by DTA analysis. Beside of this, the experimental results demonstrate the effects of mechanical milling parameters, atmosphere and lubricant, to the structure and to the size of the resultant particles and the change of magnetic behavior of the iron-oxide and iron nanoparticles when they approach to superparamagnetic region, especially in single domain region. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)