This review article first presents a summary of current understanding of the magnetic properties and intrinsic ferromagnetism of transition-metal (TM)-doped ZnO films, which are typical diluted magnetic oxides used in spintronics. The local structure and magnetic behavior of TM-doped ZnO are strongly sensitive to the preparation parameters. In the second part, we discuss in detail the effects of doping elements and concentrations, oxygen partial pressure, substrate and its orientation and temperature, deposition rate, post-annealing temperature and co-doping on the local structure and subsequent ferromagnetic ordering of TM-doped ZnO. It is unambiguously demonstrated that room-temperature ferromagnetism is strongly correlated with structural defects, and the carriers involved in carrier-mediated exchange are by-products of defects created in ZnO. The third part focuses on recent progress in TM-doped ZnO-based spintronics, such as magnetic tunnel junctions and spin field-effect transistors, which provide a route for spin injection from TM-doped ZnO to ZnO. Thus, TM-doped ZnO materials are useful spin sources for spintronics.

Ferromagnetism and possible application in spintronics of transition-metal-doped ZnO films

Nanoparticles of zinc oxide (ZnO) are increasingly recognized for their utility in biological applications. In this study, the high-energy ball milling (HEBM) technique was used to produce nanoparticles of ZnO from its microcrystalline powder. Four samples were ball milled for 2, 10, 20, and 50 hours, respectively. The structural and optical modifications induced in the 'as synthesized' nanomaterials were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and photoluminescence emission spectra (PL). SEM and TEM results show a gradual decrease in particle size from around 600 to ∼30 nm, with increased milling time. The initial microstructures had random shapes, while the final shape became quite spherical. XRD analysis showed ZnO in a hexagonal structure, broadening in the diffracted peaks and going from larger to smaller particles along with a relaxation in the lattice constant c. The value of c was found to increase from 5.204 to 5.217 A with a decrease in particle size (600 to ∼30 nm). PL result showed a new band at around 365 nm, whose intensity is found to increase as the particles size decreases. These remarkable structural and optical modifications induced in ZnO nanoparticles might prove useful for various applications. The increase in c value is an important factor for increasing the antibacterial effects of ZnO, suggesting that the HEBM technique is quite suitable for producing these nanoparticles for this purpose.

/pdf/high-energy-ball-milling-technique-for-zno-nanoparticles-as-3513u6godv.pdf

High-energy ball milling technique for ZnO nanoparticles as antibacterial material.

We review and critique the recent developments on multifunctional oxide materials, which are gaining a good deal of interest. Recongnizing that this is a vast area, the focus of this treatment is mainly on high-κ dielectric, ferroelectric, magnetic, and multiferroic materials. Also, we consider ferrimagnetic oxides in the context of the new, rapidly developing field of negative-index metamaterials. This review is motivated by the recent resurgence of interest in complex oxides owing to their coupling of electrical, magnetic, thermal, mechanical, and optical properties, which make them suitable for a wide variety of applications, including heat, motion, electric, and magnetic sensors; tunable and compact microwave passive components; surface acoustic wave devices; nonlinear optics; and nonvolatile memory, and pave the way for designing multifunctional devices and unique applications in spintronics and negative refraction-index media. For most of the materials treated here, structural and physical propertie...

Oxides, Oxides, and More Oxides: High-κ Oxides, Ferroelectrics, Ferromagnetics, and Multiferroics

A series of n-type Zn1−xCuxO (x=0.02, 0.06, 0.10, and 0.12) films was prepared using direct current reactive magnetron sputtering. Magnetic measurements indicate that all the films are ferromagnetic at room temperature and the moment per Cu ion decreases with increasing copper concentration and nitrogen doping. The observed magnetic moment was 1.8μB∕Cu for Zn0.98Cu0.02O film and the transition temperature of about 350K decreased to 320K due to nitrogen doping. It can be concluded that itinerant electrons play an important role in ferromagnetism. The resistivity increased with increasing copper concentration and nitrogen doping. The anomalous Hall effect has been found for ferromagnetic materials.

Magnetic properties of n-type Cu-doped ZnO thin films

In this paper, Ni-doped ZnO (Zn1-xNixO, in which 0 £ x £ 0.05) diluted magnetic semiconductors nanoparticles are prepared by an ultrasonic assisted sol-gel process. Transmission electron microscopy shows sphere- like nanoparticles with an average size of about 25 nm. From the analysis of X-ray diffraction, the Ni-doped ZnO nanoparticles are identified to be a wurtzite structure, but impurity phases are observed when the Ni content x reaches 0.05. Sample structures are further studied by Raman spectra, from which a broad and strong Raman band in the range of 500-600 cm -1 is observed in Zn1-xNixO. With the increment of x, wurtzite structures degrade gradually. The magnetic properties are measured using superconducting quantum interference device at room temperature; the Zn1-xNix O( x £ 0.02) nanoparti- cles show ferromagnetism. However, for the sample of Zn0.95Ni0.05O, paramagnetism is observed, which may be ascribed to ferromagnetic-antiferromagnetic competition.

Synthesis, structure, and room-temperature ferromagnetism of Ni-doped ZnO nanoparticles

High-quality Ni-doped ZnO thin films of single phase with preferred c-axis growth orientation were formed on Si (100) substrates by pulsed-laser deposition at room temperature. The films exhibited room-temperature ferromagnetic behaviors with saturation magnetic moment per Ni atom of 0.37μB,0.26μB,0.25μB and 0.21μB for the Ni concentration of 1, 3, 5, and 7 at. %, respectively. The decrease of ferromagnetism with doping concentration demonstrates that ferromagnetism observed at room temperature is an intrinsic property of Ni–ZnO thin films, not from any secondary phase.

Doping concentration dependence of room-temperature ferromagnetism for Ni-doped ZnO thin films prepared by pulsed-laser deposition

Highly c-axis oriented ZnO thin films were deposited by laser ablating Zn target in oxygen atmosphere at room temperature. Changes of c-axis lattice constant and optical energy gap caused by oxygen defects were studied via the control of oxygen vacancy concentration afforded by changing oxygen pressure in the deposition process. The results show that ZnO thin films prepared at room temperature have a very strong preferred c-axis growth orientation. As oxygen pressure increases, the lattice constant c decreases, and optical energy gap shifts towards higher energy values.

Changes of structure and optical energy gap induced by oxygen pressure during the deposition of ZnO films

Magnetocrystalline Anisotropy of Epitaxially Grown Ferh/Mgo(001) Films

The invention relates to a method for preparing the composite film which can reduce the quanta point excited voltage, belonging to the advanced photoelectric material. The invention via adding the ferroelectric material with high dielectric constant and the lighting quanta to be intercross deposited, to attain the composite structure whose quanta point is embedded into the ferroelectric film. The invention uses the part field effect to improve the electric field strength inside the quanta point; and uses the sulfur as protective layer to process vacuum heat treatment to effectively avoid the loss of sulfur in said heat treatment, and confirm the integrated structure inside the quanta, to reduce the excited voltage and enlarge the application of electroluminescent film material and device.

Preparation method of composite film capable of reducing exciting voltage of quantum spots

A heat treating method for preparing the glass able to emit strong blue influorescence from its surface includes such steps as polishing both surfaces of quartz glass, sufficient contact between the polished quartz glass and the mixture of ZnO powder and MnO powder, heating the quartz glass whose surfaces carry said powders to 1000-1200 deg.C, holding the temp for 1-3 hr, and polishing.

Process for preparing glass of lightening strong blue fluorescence on surface

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