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11.
The magnetic properties of diluted magnetic semiconductors (DMSs) are calculated from first-principles by mapping the ab initio results on a classical Heisenberg model. By using the Korringa–Kohn–Rostoker coherent potential approximation method within the local density approximation, the electronic structure of (Ga,Mn)N and (Ga,Mn)As is calculated. Effective exchange coupling constants Jijs are calculated by using the formula of Liechtenstein et al. (A.~I. Liechtenstein, M. I. Katsnelson, V. P. Antropov, and V. A. Gubanov, 1987, J.~Magn. Magn. Mater. Vol. 67, p. 65). It is found that the range of the exchange interaction in (Ga,Mn)N is very short due to the exponential decay of the impurity wave function in the gap. On the other hand, in (Ga,Mn)As, the interaction is weaker but long ranged because the extended valence hole states mediate the ferromagnetic interaction. Monte Carlo simulations show that the TC values of (Ga,Mn)N are very low since percolation is difficult to achieve for small concentrations and the mean field approximation strongly overestimates TC. Even in (Ga,Mn)As the percolation effect is still important. 相似文献
12.
《Ceramics International》2017,43(2):1997-2003
The single-phase Ni-doped PbPdO2 films with a body-centered orthorhombic structure were synthesized by the sol-gel spin-coating method and an oxidation treatment. The films with a thickness of about 440 nm were found to have a nanograin structure and large amount of Pb vacancies. The valence states of Ni and Pd ions within the Ni-doped PbPdO2 films were very close to 2+, while the Pb ions exhibited a mixed valence between 2+ and 4+. The existence of Pb vacancies and the low electronegativity of Pb2+ ion resulted in the increase of the valence of Pb ions. The analysis of the magnetic properties indicated that the magnetisms of the single-phase Ni-doped PbPdO2 nanograin films were all composed of the ferromagnetism and the paramagnetism. The ferromagnetism enhanced with the calcination temperature increasing and could be retained up to 380 K. A carrier-mediated mechanism bridged to the bound magnetic polaron model based on the Pb vacancies, the doped Ni ions and the Pb ions with a valence higher than 2+ were used to explain the magnetic origin of these Ni-doped PbPdO2 nanograin films. 相似文献
13.
硫族钙钛矿是一类新兴的半导体功能材料,具有独特的电子结构与光电性质。本文采用溶胶-凝胶法结合化学气相反应的方法制备了硫族钙钛矿BaZrS3纳米结构,并且借助掺杂的方法获得了BaZr1-xFexS3磁性半导体,并对其结构和光、磁学等性能进行研究。结果表明,对氧化物钙钛矿BaZrO3进行硫化处理,即用同族的S元素替代O元素,样品仍然可以表现出钙钛矿结构,而且硫化处理可以起到降低带隙宽度的作用。同时用具有局域磁矩的3d过渡族金属元素,如Fe进行钙钛矿B位阳离子掺杂,通过控制Fe的掺杂量同样可以系统地调控样品的带隙宽度,而且对于BaZr99.7Fe0.03S3和BaZr99.5Fe0.05S3样品表现出了室温铁磁性。 相似文献
14.
Abdullah Ameen Saad Hassan Wasi Khan Shahid Husain Pooja Dhiman Mahavir Singh 《International Journal of Applied Ceramic Technology》2020,17(5):2430-2438
In this work, the physical properties of nanocrystalline samples of La0.7Sr0.3Mn1−xFexO3 (0.0 ≤ x ≤ 0.20) perovskite manganites synthesized by the reverse micelle (RM) technique were explored in detail. The phase purity, crystal structure, and crystallite size of the samples were determined using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. All the samples had rhombohedral crystal structure and crystallite size increased with increase in Fe content in La0.7Sr0.3MnO3. The scanning electron micrographs (SEMs) exhibited smooth surface morphology and nonuniform shape of the particles. The optical properties studied using UV-visible absorption spectroscopy revealed a decrease in the absorbance and optical band gap with an increase in Fe content in La0.7Sr0.3MnO3 compound. The temperature-dependent resistivity measurements revealed semiconducting nature of x = 0 and 0.1 samples up to the studied temperature range, while a metal-to-insulator transition was observed at higher Fe doping. Magnetic studies revealed weak ferromagnetism in all the samples and a reduction in the maximum magnetization with an increase in Fe content. A close correlation between electrical transport and magnetic properties was observed with the doping of Fe ion in La0.7Sr0.3MnO3 at Mn site. These results advocate strong interactions associated with the double exchange mechanism among Fe3+ and Mn3+ ions. 相似文献
15.
采用溶胶-凝胶法制备了不同粒径的纯净单相钙钛矿型BiFeO3纳米微粒. X射线衍射分析表明,BiFeO3纳米微粒仍为菱方结构,但晶格畸变随颗粒尺寸的减小而增大. 磁测量显示,BiFeO3纳米微粒具有明显弱铁磁性,且弱铁磁性随温度升高显著降低. 弱铁磁性的自发磁化强度随温度升高呈线性下降,磁化强度和磁化率均随颗粒尺寸的减小而增大. 穆斯堡尔谱分析揭示,颗粒愈小,自旋倾角愈大,其分布也愈宽. 从纳米微粒小尺寸效应和表面效应入手,讨论了BiFeO3纳米微粒结构与磁结构和弱铁磁性的关系. 相似文献
16.
Zr doped ZnO nanoparticles are prepared by the sol-gel method with post-annealing. X-ray diffraction results show that all samples are the typical hexagonal wurtzite structure without any other new phase, as well as the Zr atoms have successfully entered into the ZnO lattices instead of forming other lattices. Magnetic measurements indicate that all the doping samples show room temperature ferromagnetism and the pure ZnO is paramagneism. The results of Raman and X-ray photoelectron spectroscopy indicate that there are a lot of oxygen vacancies in the samples by doping element of Zr. It is considered that the observed ferromagnetism is related to the doping induced oxygen vacancies. 相似文献
17.
Electrodes: Ferromagnetic,Folded Electrode Composite as a Soft Interface to the Skin for Long‐Term Electrophysiological Recording (Adv. Funct. Mater. 40/2016)
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Kyung‐In Jang Han Na Jung Jung Woo Lee Sheng Xu Yu Hao Liu Yinji Ma Jae‐Woong Jeong Young Min Song Jeonghyun Kim Bong Hoon Kim Anthony Banks Jean Won Kwak Yiyuan Yang Dawei Shi Zijun Wei Xue Feng Ungyu Paik Yonggang Huang Roozbeh Ghaffari John A. Rogers 《Advanced functional materials》2016,26(40):7280-7280
18.
Wei Yu Zishen Wang Xiaoxu Zhao Junyong Wang Tun Seng Herng Teng Ma Zhiyu Zhu Jun Ding Goki Eda Stephen J. Pennycook Yuan Ping Feng Kian Ping Loh 《Advanced functional materials》2020,30(31)
Chemical exfoliation has been used for the fast and large‐scale production of 2D nanosheets from graphene and transition metal dichalcogenides; however, it is rarely used for domain engineering of exfoliated nanosheets. Herein, it is found that the use of large sized molecular intercalants during electrochemical intercalation induce atomic row dislocation and parallel mirror twin boundaries (MTBs) on an otherwise pristine rhenium disulfide (ReS2) crystal, such that the exfoliated flakes possess a parallel, multi‐domain structure. These domains can be distinguished under a polarized microscope owing to the intrinsic in‐plane optical dichroic properties of ReS2, thereby affording a way to track the number of domains introduced versus the size of the molecular intercalant during electrochemical exfoliation. Ferromagnetism is detected on the intercalated sample using large sized molecular intercalants. Density function theory suggests that these may be due to the coupled effects of lattice strain and S vacancies in the MTBs. 相似文献
19.
20.
We have studied the optical and magnetic properties of ytterbium implanted GaN epilayer grown on(0001)sapphire by metalorganic chemical vapor by deposition(MOCVD).Samples were implanted at room temperature with Yb ions at dose 4x1015 cm-2 and energy of 150 keV.The implanted samples were annealed at 1000 ℃ in N2 at atmospheric pressure to recover implantation damages.The photoluminescence (PL),PL excitation(PLE),and PL kinetics have been studied with continuous and pulse photo-excitations in 360-1100 nm spectral range at different temperatures.The characteristic Yb3+ion emission spectra were observed in the spectral range between 970-1050 nm.Theoretical fittings of the experimental PL temperature and PL kinetics data suggest that Yb3+ions are involved in at least two major luminescence centers.The PLE spectra indicate that excitation of the Yb3+ion occurs via electron-hole pair generation and complex processes.Magnetization versus magnetic field curves shows an enhancement of magnetic order for Yb-implanted samples in 5 K to 300 K temperature range.The Yb-implanted GaN sample showing weak ferromagnetic behavior was compared with the ferromagnetic in situ doped GaYbN material. 相似文献