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Room temperature diluted ferromagnetic semiconductor is a very promising candidate for spintronics applications. In this work, we present the cobalt ion implanted ZnO epitaxial thin film under controlled annealing temperature to investigate the origin of ferromagnetism in this system. For the as-implanted sample a metallic cobalt cluster was observed. After annealing at 700[degrees]C, the Co atoms were to substitute the Zn sites of the ZnO matrix and exhibited a spontaneous room temperature ferromagnetism. However the XMCD measurements on the annealed samples show the cobalt element is almost paramagnetism at 26 K. The result might indicate oxygen vacancies caused ferromagnetism of intrinsic dilute magnetic semiconductors in the sample of the Co-implanted ZnO. Index Terms--Co-doped ZnO, magnetic circular dichroism (XMCD), magnetic semiconductors.

The performance of resistance random access memory (RRAM) devices based on spin-coated sol-gel-derived zinc oxide (ZnO) thin films is examined. The devices are fabricated on a flexible plastic substrate and have displayed excellent durability upon repeated bending tests, thus showing their potential for flexible low-cost memory devices.

The effect of Al doping on the magnetic properties of Zn(Cu)O based diluted magnetic semiconducting thin films is examined. The results have shown that carrier induced exchange is not directly responsible for the magnetic properties of these materials.

The implantation of ZnO with dilute, radioactive [super 57][Mn.sup.+] ions has shown that Fe atoms are in a magnetically ordered atomic surrounding with ordering temperatures >>600 K. The results have challenged the concepts regarding the modeling of magnetic ordering in 3d-metal doped oxides and have shown this role of vacancies in the magnetism to be a general

The study result from comparable magnetotransport measurement on Co-doped ZnO and Mn-doped ZnO films is reported. The saturated anomalous Hall resistivity observed for Co-doped ZnO was found to increase with decreasing electron concentration while Mn-doped ZnO showed no anomalous Hall effect.

The epitaxial growth and properties of Co and Cu codoped ZnO thin films deposited onto sapphire c-plane single crystals by using pulsed-laser deposition are studied. The presence of high oxygen vacancies in the films have allowed possible defect mediated mechanisms for mediating exchange coupling of the dopant ions resulting in room temperature ferromagnetism.

A study is conducted of the room temperature effective permeability tensor components of fine-grained composites composed of polycrystalline magnetic ZnO, Co, gamma- [Fe.sub.2][O.sub.3] and Ni particles and the observations on the frequency and composition dependences at various magnetic fields are reported. It is found that magnetically structured granular systems comprised of magnetic grains embedded in a nonmagnetic matrix is likely to have quite different behaviors depending on their constituents.

Study is presented to show that there is a mechanism promoting room temperature ferromagnetism (RT FM) in [Co.sub.3][O.sub.4]-ZnO bulk samples different than carrier mediation or segregated cobalt metallic clusters. This mechanism is associated with a partial reaction of ZnO and [Co.sub.3][O.sub.4] grains and appears when the starting phases ZnO and [Co.sub.3][O.sub.4] are present in the sample.

Electromagnetic emission at the very high frequency (VHF) range of 30 to 300 MHz is used to detect surface defects on outdoor polymer zinc oxide (ZnO) surge arrestors. The partial discharge related signals are recorded and studied. Since the surge arrestors are usually exposed to adverse weather conditions, the effect of moisture and pollution on the characteristics is also investigated. Samples subjected to surface pollution were created according to the IEC standard under both wet and dry conditions. The collected electromagnetic signals were sampled and analyzed using a joint time-frequency analysis tool called the Wigner-Ville distribution (WVD). The results of this work indicate that the WVD analysis can be used as a diagnostic tool for polymer ZnO surge arrestors. Index Terms--Surge arrestor, surface pollution, electromagnetic pulse, Wigner distributions.

Nanocrystals of Zn(sub (1-x))Mn(sub x)O were produced using a novel colloidal chemistry technique. The manganese ions primarily substitute zinc ions in the hexagonal ZnO lattice, and part of them are ferromagnetically coupled up to room temperature even in isolated noninteracting nanocrystals and the rest of ions are magnetically disordered or uncoupled and the study highlights the advantages of working with noninteracting single domain particles of these intriguing materials.

(Mn, Co)-codoped ZnO films are synthesized on c-sapphire (001) by a radio-frequency magnetron sputtering system in which two targets are sputtered together. X-ray diffraction measurements indicate that the films are highly c-axis oriented.

The full potential linearized augmented plane wave method is used to explore the magnetization and magnetic ordering of Co doped ZnO. Nonuniform distribution and antiferromagnetic ordering is preferred by energetically Co and both Zn and O display measurable x-ray magnetic circular dichroism spectra.

The magnetic and transport properties of Mn-doped ZnO thin films codoped with Sn are examined. Superconducting quantum interface device magnetometry measurements indicate that the films are ferromagnetic with an inverse correlation between magnetization and electron density as controlled by Sn doping.

In this article, by studying structural and magnetic properties of transition metal substituted polycrystalline ZnO samples, it is found that no bulk ferromagnetism exists for single-phase materials, contrary to the existing theories.

A new and facile procedure is developed for the preparation of colloidal ZnO-diluted magnetic semiconductor quantum dots (DMS-QDs) by alkaline-activated hydrolysis and condensation of zinc acetate solutions in dimethyl sulfoxide (DMSO). The method provides high-quality ZnO quantum dots with reasonable shape and size distributions.

A promising epitaxial growth technique, namely helicon-wave-excited plasma sputtering epitaxy (HWPSE), is proposed for the growth of ZnO epilayers. The ZnO epilayer exhibited a dominant near-band-edge photoluminescence (PL) peak at 300 K.

Copper-doped ZnO (ZnO:Cu) films are prepared on silicon substrates by filtered cathodic vacuum arc technique at room temperature using a Zn target containing 5 at. % of Cu. X-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy reveals that no ferromagnetic-related secondary could be detected in ZnO:Cu.

Four kinds of Li and Co codoped ZnO (LCZO) thin films are prepared by a sol-gel process technique. X-ray diffraction results reveal that the LCZO thin films possess single ZnO wurtzite structure and c-axis preferred orientation, and Li and Co ions substitute for the Zn sites without changing the wurtzite structure.

Polycrystalline samples of In and Co codoped ZnO ([Zn.sub.1-x][In.sub.x][Co.sub.0.075] O; 0.010 [less than or equal to] x [less than or equal to] 0.020) oxide were prepared by solid-state synthesis technique. Phase purity and structure refinement done by means of the Rietveld analysis technique shows that both Co and In substitute properly into Zn positions. In doping, increased bulk conductivity of the samples at room temperature indicates an increase of charge carrier concentration. All samples showed paramagnetic behavior following Curie-Weiss law at close to room temperatures, with short range antiferromagnetic interaction with [THETA] [approximately equal to] -200 K. Effective magnetic moment ([[micro].sub.eff]) calculations showed a strong orbital contribution to the value of [[micro].sub.eff], increasing with an increase of In content (x). Index Terms--Paramagnetic materials, spintronics.

[Zn.sub.1-x][Fe.sub.x]O (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.10) compounds were fabricated by the sol-gel method. The crystal structure and magnetic properties were investigated as a function of doped Fe concentration. Specifically, we have used hydrogen treatment for the control of phase separation. The X-ray diffraction patterns show that the wurzite structure of ZnO does not change for the doping range below x = 0.07. Furthermore, we could not find any Fe cluster or phase separation in the X-ray diffraction patterns. The Fe-doped ZnO indicate ferromagnetic behaviors with the Curie temperature higher than room temperature. Then, the magnetic moment per Fe atom increased with increasing Fe concentration. Index Terms--Diluted magnetic semiconductor (DMS), ferromagnetic, hydrogen treatment, spintronics.

Structural and magnetic properties are studied for polyscrystalline Zn(sub 1-x)Mn(sub x)O (x=0.02,0.03,0.05). The results state that single phase samples show paramagnetic Curie-Weiss behavior.

The comparative analysis of magnetization, resistivity and magnetoresistance measurements of ZnO:Co structures is done. The structures are diluted magnetic semiconductor (DMS) superlattices at small thickness of Co layers in the multilayer samples.

The Perdew-Burke-Ernzerhof form of generalized gradient approximation is used for analyzing the electronic and magnetic properties of (Mn,N)-codoped ZnO within the framework of the density functional theory. The analysis of geometrical configurations for (Mn,N)-codoped ZnO has shown that the ground state is changed from no-metallic AFM to half-metallic ferromagnetic, which is because of the strong hybridization between N sp and Mn 3d states.

The growth, as well as the structural and magnetic properties exhibited by the epitaxial [Fe.sub.3][O.sub.4/ZnO and ZnO/[Fe.sub.3][O.sub.4] bilayers grown on c-[Al.sub.2][O.sub.3] substrate are discussed. The [Fe.sub.3][O.sub.4/ZnO bilayer is shown to be much more stable, as compared to the other bilayers.

The occurrence of high temperature ferromagnetism (FM) in ZnO nanoparticles (NPs) doped with Co-atoms is described. The studies have showed that high temperature FM is mediated by defects in the strained NPs and ZnO NPs of lower initial size has shown enhanced FM, which is attributed to size dependent doping effect.

The electronic and magnetic properties of pure and Mn-doped armchair and zigzag ZnO nanotubes are analyzed by using density functional theory with the generalized gradient approximation. The studies have shown that large magnetic moments have appeared in Mn-doped ZnO nanotubes, which are due to the hybridization between the O 2p and Mn 3d states.

Epitaxial films of ZnO doped with magnetic ion Fe and Al has shown room temperature ferromagnetic ordering. The magnitude of junction magnetoresistance has depended on the magnitude of the magnetic moment of the dilute magnetic semiconductor films and these properties are explained by stdandard spin injection theory.

Dense nanograined pure and Mn-doped [Zn.sub.1-x][Mn.sub.x]O polycrystals are prepared by the wet chemistry method from butanoate precursors. The shape of the dependence of saturation magnetization on Mn concentration is different for the Mn-doped nanograined ZnO prepared by different methods and it is controlled by the topology of grain boundary network in the ZnO polycrystals.

The structural, chemical, electrical, optical and magnetic properties of undoped ZnO thin films grown under different conditions as well as the films that are annealed in various environments are analyzed. The studies have shown that the ferromagnetic order in ZnO matrix is defect-mediated.

The structural and magnetic properties of pulsed laser deposited zinc oxide thin films are examined. The ferromagnetism has occurred from intrinsic defects in the ZnO that can be varied by manipulation of the lattice parameter.

Nanocrystalline Gd-doped ZnO thin films are prepared by using versatile pulsed spray pyrolysis method and have displayed room temperature ferromagnetism. Hysteresis measurements have shown that the Gd-doped ZnO films are magnetically anisotropic and have displayed intrinsic ferromagnetic behavior at room temperature.

Multiferroic BiFe[O.sub.3] thin film is grown on the ZnO-buffered Pt/Ti[O.sub.2]/Si[O.sub.2](100) substrate by off-axis radio frequency magnetron sputtering, where the ZnO buffer layer has produced a strong (110) texture for the BiFe[O.sub.3] thin film. The ZnO as a buffer layer for BiFe[O.sub.3] has changed the dielectric relaxation and conduction mechanisms.

The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films is analyzed by alternating the deposition of a several-nanometer-thick ZnO layer and the [O.sub.2]/Ar mixture plasma exposure, that is, layer-by-layer technique. The diffusion and effusion of oxygen atoms at the growing surface have played a role of thermal annealing, promoted the film crystallization as well as the creation and the annihilation of oxygen and zinc related defects.

A combination of the x-ray absorption structure and other techniques is employed to explain the structural, as well as the magnetic properties of the different Co:ZnO magnetic films. The presence of O vacancy is shown to play an extremely significant role in the ferromagnetic interactions of the films.

Several studies are conducted to explain the formation, as well as the different photoluminescence properties of the emissions taking place in the [Zn.sub.1-x][Co.sub.x]O layers. The suppression of excitonic emissions is shown to be extremely beneficial in the enhancement of the intraemissions taking place in these layers.

The anisotropic structural properties of periodically polarity-inverted (PPI) ZnO structures grown on patterned templates are studied. The structures at transition region have shown relationship with the anisotropic crystal quality.

Simultaneous room temperature ferroelectricity and magnetic properties are observed in (Co, Li) coimplanted ZnO films. The ionic radius difference between the dopants and host cations is used for interpreting the ferroelectricity and the magnetism is described by bound magnetic polarons mediated by electrons and defects.

The electronic structure of Cu-doped ZnO thin films, prepared with a nominal composition of [Zn.sub.1-x][Cu.sub.x]O by using spray pyrolysis method, is examined by using near-edge x-ray absorption fine structure (NEXAFS) experiments at the O K- and the Cu[L.sub.3.2]-edges and resonant inelastic x-ray scattering (RIXS) measurements at Cu [L.sub.3.2] edge. The results have shown that Cu is in mixed valence state of [Cu.sup.2+/3+][Cu.sup.1+], substituting at the Zn site and [Cu.sup.2+/3+] ions are magnetically polarized.