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This paper reports an in-depth study on nanocrystalline Gd-doped ZnO thin films synthesized using versatile pulsed spray pyrolysis method and exhibit room temperature ferromagnetism. The detailed structural and microstructural studies confirm that the doped Gd ions occupy Zn sites and the peak shift can be elucidated by charge neutrality. Optical investigation shows that the Gd doping in ZnO lattice leads to a decrease in the near band edge position due to the introduction of new unoccupied states by Gd 4f electrons. The electronic structure of the Zn1-xGdxO at the O K edge shows the evolution of pre-edge spectral features similar to cuprates and manganites, and also confirms the strong hybridization of O 2p-Gd 4f/5d states. Furthermore, the Gd M5 edge provides evidence that Gd ions are in the trivalent state. Hysteresis measurements demonstrate that the Gd-doped ZnO films are magnetically anisotropic and exhibit intrinsic ferromagnetic behavior at room temperature. Higher magnetization in 3 kOe values is observed for a field applied perpendicular to the sample surface compared to the in-plane direction. [ABSTRACT FROM AUTHOR]

The effects of oxygen concentration and film thickness were studied on the microstructural, electrical, and magnetic properties of Fe65Co35–O alloy films prepared by dc magnetron sputtering at room temperature. The films showed the best magnetic softness with a large saturation magnetization of 21.5 kG, low coercivities of 2.8 and 2.1 Oe in easy and hard axes, respectively, and a high resistivity of 2215 μΩ cm at an optimized condition of an oxygen gas flow ratio of 1.0% and a film thickness of 105 nm. Such an excellent magnetic softness can be attributed to grain refinement caused by the addition of very low dose of oxygen, which basically did not lead to the full formation of Fe and/or Co oxide phases with low saturation magnetizations. The microwave permeability measurement indicated that the addition of very low dose of oxygen could improve the response of real permeability to frequency. A high real permeability of 525 at frequency up to 1.2 GHz was obtained for the Fe65Co35–O films deposited at the optimized condition above. [ABSTRACT FROM AUTHOR]

Magnetically soft Fe-Co alloy cluster-assembled films were produced at room temperature by an energetic cluster deposition. Size-monodispersed Fe-Co alloy clusters whose average sizes ranged between 8 and 14 nm were obtained using a plasma-gas-condensation-type cluster deposition apparatus. Positively charged clusters in a cluster beam were accelerated electrically and deposited onto a negatively biased substrate together with neutral clusters from the same cluster source, leading to formation of high-density Fe-Co alloy cluster-assembled films. Magnetic properties were observed for these films prepared by changing the bias voltage. Based on the temperature dependence of magnetic coercivity, we estimated the effective magnetic anisotropy constant, Keff, and magnetic exchange length Lex (or Dex) as a function of the packing fraction in the Fe-Co cluster-assembled films: Keff decreases and Lex (or Dex) increases dramatically with the packing fraction. [ABSTRACT FROM AUTHOR]

Nb and NbN cluster-assembled films were produced by a plasma–gas–condensation cluster deposition apparatus and examined by transmission electron microscopy, electrical resistivity, and ultraviolet photoemission spectroscopy. The electron diffraction patterns of the Nb and NbN clusters displayed body-centered-cubic and NaCl-type diffraction rings, respectively. The electrical sheet resistance, R[sub □], of both Nb and NbN cluster-assembled films, however, showed no superconductivity down to 2 K. We found a linear relation in the log R[sub □] versus T[sup -1/4] plot for the Nb cluster assembly, suggesting an electron localization effect. For the NbN cluster-assembly, on the other hand, R[sub □] showed a semiconductor type temperature dependence, which is consistent with the valence electron spectra. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We systematically studied structural and magnetic characteristics of size- monodispersed Fe and oxide-coated Fe cluster assemblies with the mean cluster sizes of 7-16 nm. Transmission electron microscopy and scanning electron microscopy (SEM) observations show that the Fe clusters in the assemblies maintain their original size at room temperature. In the SEM images, a random stacking of the Fe clusters and a porous structure with a low cluster packing fraction of about 25% are observed. For the Fe cluster assemblies, magnetic coercivity (H[sub c]) at room temperature increases from 4 × 10[sup 1] to 4 × 10² Oe by increasing the mean cluster size from 7.3 to 16.3 nm. Using the experimental values of the coercivity at T ≥ 100 K and the fitting values of blocking temperature T[sub B] from H[sub c]=H[sub co] [1- (T/T[sub B])[sup 1/2]], we estimated the values of magnetic anisotropy constant K of the order of 10[sup 6] erg/cm[sup 3] from T[sub B] = KV/25k[sub B],which is larger by an order of magnitude than the bulk Fe value (5 × l0[sup 5] erg/cm[sup 3]). Such a large effective anisotropy at T ≥ 100 K is ascribed to the large surface anisotropy effects of the small clusters and the low cluster-packing fraction of the Fe cluster assemblies. For the oxide-coated Fe cluster samples, the coercivity strongly depends on the oxygen gas flow rate during deposition, cluster size, and temperature. In the case of a high oxygen gas flow rate (namely high surface-oxidized clusters), the ferrimagnetic oxide shell crystallites also affect the coercivity at T > 50 K: The hysteresis loop shift disappears, leading to a complex change in the coercivity and an enhancement of the effective anisotropy constant. [ABSTRACT FROM AUTHOR]

The effects of oxygen concentration and film thickness are analyzed on the microstructural, electrical and magnetic properties of [Fe.sub.65][Co.sub.35]-O films prepared by dc magnetron sputtering at room temperature. The magnetic softness with a large saturation magnetization is attributed to grain refinement caused by the addition of very low dose of oxygen, which has not led to the full formation of Fe and Co oxide phases with low saturation magnetizations.

The results of two size selection methods that are based on the control of interfacial interaction between nanosize particles, using either suitable ionic surfactants or nonpolar solvents, are reported. Using these methods, stable suspensions of monodispersed magnetic nanoparticles (standard deviation, sigma, below 0.2) having various diameters, were obtained.