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Register a new userSpinel ferrite nanocrystals embedded inside ZnO: magnetic, electronic and magneto-transport properties
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In this paper we show that spinel ferrite nanocrystals (NiFe2O4, and CoFe2O4) can be texturally embedded inside a ZnO matrix by ion implantation and post-annealing. The two kinds of ferrites show different magnetic properties, e.g. coercivity and magnetization. Anomalous Hall effect and positive magnetoresistance have been observed. Our study suggests a ferrimagnet/semiconductor hybrid system for potential applications in magneto-electronics. This hybrid system can be tuned by selecting different transition metal ions (from Mn to Zn) to obtain various magnetic and electronic properties.
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This paper presents the results of simulations of the magnetization field {it ac} response (at $2$ to $12$ GHz) of various submicron ferrite particles (cylindrical dots). The ferrites in the present simulations have the spinel structure, expressed here by M$_{1-n}$Zn$_{n}$Fe$_2$O$_4$ (where M stands for a divalent metal), and the parameters chosen were the following: (a) for $n=0$: M = { Fe, Mn, Co, Ni, Mg, Cu }; (b) for $n=0.1$: M = { Fe, Mg } (mixed ferrites). These runs represent full 3D micromagnetic (one-particle) ferrite simulations. We find evidences of confined spin waves in all simulations, as well as a complex behavior nearby the main resonance peak in the case of the M = { Mg, Cu } ferrites. A comparison of the $n=0$ and $n=0.1$ cases for fixed M reveals a significant change in the spectra in M = Mg ferrites, but only a minor change in the M = Fe case. An additional larger scale simulation of a $3$ by $3$ particle array was performed using similar conditions of the Fe$_3$O$_4$ (magnetite; $n=0$, M = Fe) one-particle simulation. We find that the main resonance peak of the Fe$_3$O$_4$ one-particle simulation is disfigured in the corresponding 3 by 3 particle simulation, indicating the extent to which dipolar interactions are able to affect the main resonance peak in that magnetic compound.
In this paper, the reported experimental data in [Sci. Rep., 2012, 2, 533] related to electrical transport properties in bulk ZnO, ZnMgO/ZnO, and ZnMgO/ZnO/ZnMgO single and double heterostructures were analyzed quantitatively and the most important scattering parameters for controlling electron concentration and electron mobility were obtained. Treatment of intrinsic mechanisms included polar-optical phonon scattering, piezoelectric scattering and acoustic deformation potential scattering. For extrinsic mechanisms, ionized impurity, dislocation scattering, and strain-induced fields were included. For bulk ZnO, the reported experimental data were corrected for removing the effects of a degenerate layer at the ZnO/sapphire interface via a two layer Hall effect model. Also, donor density, acceptor density and donor activation energy were determined via the charge balance equation. This sample exhibited hopping conduction below 50K and dislocation scattering closely controlled electron mobility closely. The obtained results indicated that the enhancement of electron mobility in double sample, compared with the single one, can be attributed to the reduction of dislocation density, two dimensional impurity density in the potential well due to background impurities, and/or interface charge and strain-induced fields, which can be related to better electron confinement in the channel and enhancement in the sheet carrier concentration of 2DEG in this sample.
Multilayer films of ZnO with Co were deposited on glass substrates then annealed in a vacuum. The magnetisation of the films increased with annealing but not the magnitude of the magneto-optical signals. The dielectric functions for the films were calculated using the MCD spectra. A Maxwell Garnett theory of a metallic Co/ZnO mixture is presented. The extent to which this explains the MCD spectra taken on the films is discussed.
We present results of magneto-optical measurements and theoretical analysis of shallow bound exciton complexes in bulk ZnO. Polarization and angular dependencies of magneto-photoluminescence spectra at 5 T suggest that the upper valence band has $Gamma_7$ symmetry. Nitrogen doping leads to the formation of an acceptor center that compensates shallow donors. This is confirmed by the observation of excitons bound to ionized donors in nitrogen doped ZnO. The strongest transition in the ZnO:N ($I_9$ transition) is associated with a donor bound exciton. This conclusion is based on its thermalization behavior in temperature-dependent magneto-transmission measurements and is supported by comparison of the thermalization properties of the $I_9$ and $I_4$ emission lines in temperature-dependent magneto-photoluminescence investigations.
A brief review is given of recent positron studies of metal and semiconductor nanocrystals. The prospects offered by positron annihilation as a sensitive method to access nanocrystal (NC) properties are described and compared with other experimental methods. The tunability of the electronic structure of nanocrystals underlies their great potential for application in many areas. Owing to their large surface-to-volume ratio, the surfaces and interfaces of NCs play a crucial role in determining their properties. Here we focus on positron 2D angular correlation of annihilation radiation (2D-ACAR) and (two-detector) Doppler studies for investigating surfaces and electronic properties of CdSe NCs.
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