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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.

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 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

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.

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.