Papers by Keyword: Room Temperature Ferromagnetism

Abstract: X-ray diffractometer, field emission scanning electron microscope (SEM, Hitachi S-4800), laser confocal micro-region Raman spectrometer and vibration sample magnetometer were used to systematically study the effects of polyethyleneimine concentrations and exposure time on the morphology and size of ZnO nanowire arrays. The photoelectric property and the relationship between the morphology of nanowire arrays and ferromagnetism at room temperature were also analyzed. Under 15 min exposure time, when the polyethyleneimine concentration is 2.25 g / L, the obtained ZnO nanowire array film exhibits the smallest size, the optimal density and vertical orientation. According to the study of luminescence and room temperature magnetism, it is shown that the optical and ferromagnetic property are related to the variation tendency of oxygen defects and surface defects of the ZnO nanowires.

Abstract: polycrystalline Cu_xY_yO_z are made through solid state reaction. Ferromagnetism is found in this YCuO system at room temperature. The ferromagnetism quite probably originates from Cu₂Y₂O₅ , the Copper Yttrium Oxide. The average magnetic moment per Cu²⁺ is estimated to be 0.04μ_B. Itinerant electron magnetism is a rational explaination for the observed ferromagnetism. The experiment shows that the excessive amount of Cu may lead more defects and further distortion in the lattice and decrease the exchange interaction. This reminds us that the Copper Yttrium Oxide is a substance not only should be avoided in fabricating YBCO superconductors but also should be considered as a potential substance of magnetic semiconductor.

Abstract: Ti_0.985Co_0.015O_2-δ thin films are deposited at 0, 0.1, 1 and 300 mTorr oxygen partial pressures by pulsed laser deposition (PLD) technique. Glancing angle x- ray diffraction (GAXRD) and micro-Raman spectroscopy show that the phase changes from rutile to anatase with increasing oxygen partial pressure. From Rutherford backscattering spectroscopic (RBS) technique, O to (Ti+Co) atomic ratio is found to increase with increasing oxygen partial pressure. Further, the simulation of RBS data while reveals non-uniform distribution of Co throughout the film deposited at 0 and 0.1 mTorr oxygen partial pressures, at 1 and 300 mTorr oxygen partial pressure, Co distribution is found to be uniform. Magnetic measurements confirm the room temperature ferromagnetism (RTFM) in all the films independent of the phase. Magnetic force microscopy (MFM) further supports the ferromagnetic nature of the films. We attribute the ferromagnetism in the films to be arisen from defects like oxygen vacancies rather than any contamination or Co clustering.

Abstract: Room temperature ferromagnetism was observed in Fe-doped In2O3 films deposited on fused quartz substrates by radiofrequency magnetron sputtering in N2 and O2 atmosphere, respectively. Results show that with increasing the O2 and N2 flux, the lattice constant increases, the optical band gap decreases, and the ferromagnetism weakens. Moreover, the decrease in the saturation magnetization for films deposited in N2 atmosphere is more apparent than that deposited in O2 atmosphere. We think the reason is that in our Fe-doped In2O3 films the ferromagnetism is mainly mediated by the oxygen vacancies, and as an acceptor defect, N ions can decrease the concentration of the oxygen vacancies to a greater extent than the O ions.

Abstract: ZnO semiconductor doped with a few per cent of some transition metal ions can exhibit above room temperature ferromagnetism, transforming it into a very promising candidate for future spin-electronic applications. In the present article we have compared the electronic structure of two polycrystalline ZnMnO pellets doped with diluted Mn concentration (2% and 4%), carefully characterized by SQUID and XRD, including Rietveld refinement. The characterization measurements established that the samples have the ZnO lattice with ZnS type Wurtzite hexagonal symmetry and no detectable impurities. The samples exhibit distinctly different magnetic properties. The 2% sample displayed a clear FM ordering at 300 K while the 4% sample did not show any ordering down to 5K. The electronic structure of these two samples has been investigated using Mn L23 x-ray absorption spectroscopy, Zn 2p and 3p, Mn 3p and O 1s x-ray photoemission spectroscopy. Our aim was to find out how the changes in the electronic structure can correlate to the observed magnetic properties in such diluted magnetic semiconductor materials. The results show that most of the Mn ions of the ferromagnetic sample are in the divalent state. For the higher Mn percent nonmagnetic sample, a larger contribution of higher oxidation Mn states are dominant and the oxygen content also increases. The two factors can be correlated to the suppressed ferromagnetism, though it is hard to pinpoint that which of these two weighs more in the suppression mechanism.

Abstract: A series of Zn0.95-xCo0.05AlxO (x=0, 0.01, 0.02, 0.05, 0.08, 0.10) powders with different percentages of aluminum was fabricated using the sol-gel method. X-ray diffraction (XRD) revealed that the Co ions and Al ions substitute for Zn2+ ions without changing the wurtzite structure. No impurity phases were found. No clusters or precipitates of cobalt or aluminum were found using scanning electron microscope analysis. Fourier transform-infrared reflection (FT-IR) spectrometry was used to examine the infrared transmission properties and revealed that Co ions were incorporated into the lattice as Co2+ substituting for Zn2+. Ferromagnetic behavior in the samples was obtained at room temperature. As the Al content x increased, the room temperature ferromagnetism of the samples was reduced, and when x increased to 0.08, the room temperature ferromagnetism disappeared.

Abstract: Zn-Mn-O semiconductor crystallites with nominal manganese concentration x = 0.01, 0.02, 0.04 and 0.10 were synthesized by a solid state reaction route using oxalate precursors. Thermal treatment procedure was carried out in air at different temperatures in the range 400 - 900°C. The samples were investigated by X-ray diffraction, magnetization measurements and electron paramagnetic resonance. X-ray analysis reveals that dominant crystal phase in the Zn-Mn-O system corresponds to the wurtzite structure of ZnO. Room temperature ferromagnetism is observed in the Zn-Mn-O samples with lower manganese concentration, x ≤ 0.04, thermally treated at low temperature (500°C). Saturation magnetization in the sample with x = 0.01 is found to be 0.05 μB/Mn. The ferromagnetic phase seems to be developed by Zn diffusion into Mn-oxide grains.