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Daniel R Gamelin - One of the best experts on this subject based on the ideXlab platform.
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direct kinetic correlation of carriers and Ferromagnetism in co2 zno
Physical Review Letters, 2006Co-Authors: Kevin R Kittilstved, Dana A Schwartz, Allan C Tuan, Steve M Heald, Scott A Chambers, Daniel R GamelinAbstract:In only a few cases have the key factors controlling long-range magnetic ordering in diluted magnetic semiconductors (DMSs) been unambiguously identified. In Ga1� xMnxAs, the identification and variation of critical experimental parameters has culminated in a testable microscopic model describing hole-mediated magnetic ordering in this and several related manganese-doped III-V semiconductors [1]. The recent discovery of high-Curietemperature (TC) Ferromagnetism in doped oxide semiconductors has stimulated intense experimental and theoretical interest in these materials [2]. In contrast with Ga1� xMnxAs, a clear consensus has not yet been reached about the relationship between carriers (bound or free) and Ferromagnetism in these doped oxides. Only through identification and systematic variation of key compositional parameters will a significant advance in the understanding of high-TC Ferromagnetism in doped oxides be realized. In this Letter, we demonstrate that the native shallow donor interstitial zinc (Zni) is capable of activating high-TC Ferromagnetism in Co 2� -doped ZnO (Co 2� : ZnO). The Zni concentration in an oriented epitaxial thin film of Co 2� : ZnO was systematically varied by controlled oxidative removal of these shallow donors at elevated temperatures. A direct correlation between the 300 K ferromagnetic saturation moment (MS) and the concentration of Zni was observed. The experimental activation barriers clearly identify the diffusion of Zni as the rate-determining process in the oxidative quenching of Ferromagnetism in Co 2� : ZnO. These results provide conclusive evidence that the high-TC Ferromagnetism in Co 2� : ZnO is mediated by
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electronic structure origins of polarity dependent high tc Ferromagnetism in oxide diluted magnetic semiconductors
Nature Materials, 2006Co-Authors: Kevin R Kittilstved, Daniel R GamelinAbstract:Electronic structure origins of polarity-dependent high- T C Ferromagnetism in oxide-diluted magnetic semiconductors
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chemical manipulation of high t c Ferromagnetism in zno diluted magnetic semiconductors
Physical Review Letters, 2005Co-Authors: Kevin R Kittilstved, Nick S Norberg, Daniel R GamelinAbstract:: We report the use of targeted p- and n-type chemical perturbations to manipulate high-T(C) Ferromagnetism in Mn(2+):ZnO and Co(2+):ZnO in predictable and reproducible ways. We demonstrate a clear correlation between nitrogen and high-T(C) Ferromagnetism for Mn(2+):ZnO and an inverse correlation for Co(2+):ZnO, both as predicted by recent theoretical models. These chemical perturbations reveal rich possibilities for exerting external control over high-T(C) spin ordering in diluted magnetic semiconductors.
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high temperature Ferromagnetism in ni2 doped zno aggregates prepared from colloidal diluted magnetic semiconductor quantum dots
Physical Review Letters, 2003Co-Authors: Pavle V Radovanovic, Daniel R GamelinAbstract:Ferromagnetism with T c > 350 K is observed in the diluted magnetic semiconductor Ni 2 + :ZnO synthesized from solution. Whereas colloidal Ni 2 + :ZnO nanocrystals are paramagnetic, their aggregation gives rise to robust Ferromagnetism. The appearance of Ferromagnetism is attributed to the increase in domain volumes and the generation of lattice defects upon aggregation. The unusual temperature dependence of the magnetization coercivity is discussed in terms of a temperature-dependent exchange interaction involving paramagnetic Ni 2 + ions.
Juan P Dehollain - One of the best experts on this subject based on the ideXlab platform.
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nagaoka Ferromagnetism observed in a quantum dot plaquette
Nature, 2020Co-Authors: Juan P Dehollain, Uditendu Mukhopadhyay, V P Michal, Yu Wang, Bernhard Wunsch, C ReichlAbstract:Engineered, highly controllable quantum systems are promising simulators of emergent physics beyond the simulation capabilities of classical computers1. An important problem in many-body physics is itinerant magnetism, which originates purely from long-range interactions of free electrons and whose existence in real systems has been debated for decades2,3. Here we use a quantum simulator consisting of a four-electron-site square plaquette of quantum dots4 to demonstrate Nagaoka Ferromagnetism5. This form of itinerant magnetism has been rigorously studied theoretically6–9 but has remained unattainable in experiments. We load the plaquette with three electrons and demonstrate the predicted emergence of spontaneous ferromagnetic correlations through pairwise measurements of spin. We find that the ferromagnetic ground state is remarkably robust to engineered disorder in the on-site potentials and we can induce a transition to the low-spin state by changing the plaquette topology to an open chain. This demonstration of Nagaoka Ferromagnetism highlights that quantum simulators can be used to study physical phenomena that have not yet been observed in any experimental system. The work also constitutes an important step towards large-scale quantum dot simulators of correlated electron systems. A quantum dot device designed to host four electrons is used to demonstrate Nagaoka Ferromagnetism—a model of itinerant magnetism that has so far been limited to theoretical investigation.
Hui Li - One of the best experts on this subject based on the ideXlab platform.
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copper doped aln polycrystalline powders a class of room temperature ferromagnetic materials
Solid State Communications, 2011Co-Authors: Hui Li, Xiaolong Chen, Bo Song, W J WangAbstract:Abstract Cu-doped AlN polycrystalline samples were synthesized by a solid-state reaction. X-ray diffraction analysis revealed the hexagonal structure of the doped samples. Photoluminescence measurements reveal the substitution of Cu for Al in the AlN lattice. Clear hysteresis loops are observed in the M – H curves for the samples at 300 K, revealing room temperature Ferromagnetism of the samples. Our experimental results verify that room temperature Ferromagnetism is an intrinsic property of Cu-doped AlN.
J B Yi - One of the best experts on this subject based on the ideXlab platform.
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Room temperature Ferromagnetism in Teflon due to carbon dangling bonds
Nature Communications, 2012Co-Authors: Y. W. Ma, D. Q. Gao, D. S. Xue, J.-m. Xue, Xiao Ming Liu, Tun Seng Herng, J B Yi, Y P Feng, Y H Lu, J. Y. OuyangAbstract:The Ferromagnetism in many carbon nanostructures is attributed to carbon dangling bonds or vacancies. This provides opportunities to develop new functional materials, such as molecular and polymeric ferromagnets and organic spintronic materials, without magnetic elements (for example, 3d and 4f metals). Here we report the observation of room temperature Ferromagnetism in Teflon tape (polytetrafluoroethylene) subjected to simple mechanical stretching, cutting or heating. First-principles calculations indicate that the room temperature Ferromagnetism originates from carbon dangling bonds and strong ferromagnetic coupling between them. Room temperature Ferromagnetism has also been successfully realized in another polymer, polyethylene, through cutting and stretching. Our findings suggest that Ferromagnetism due to networks of carbon dangling bonds can arise in polymers and carbon-based molecular materials.
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defect induced magnetism in undoped wide band gap oxides zinc vacancies in zno as an example
AIP Advances, 2011Co-Authors: Guozhong Xing, J B Yi, Yunhao Lu, Yufeng Tian, C C Lim, Yongfeng Li, G P Li, D Wang, B Yao, Jun DingAbstract:To shed light on the mechanism responsible for the weak Ferromagnetism in undoped wide band gap oxides, we carry out a comparative study on ZnO thin films prepared using both sol-gel and molecular beam epitaxy (MBE) methods. Compared with the MBE samples, the sol-gel derived samples show much stronger room temperature Ferromagnetism with a magnetic signal persisting up to ∼740 K, and this ferromagnetic order coexists with a high density of defects in the form of zinc vacancies. The donor-acceptor pairs associated with the zinc vacancies also cause a characteristic orange-red photoluminescence in the sol-gel films. Furthermore, the strong correlation between the Ferromagnetism and the zinc vacancies is confirmed by our first-principles density functional theory calculations, and electronic band alteration as a result of defect engineering is proposed to play the critical role in stabilizing the long-range Ferromagnetism.
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Ferromagnetism in dilute magnetic semiconductors through defect engineering li doped zno
Physical Review Letters, 2010Co-Authors: J B Yi, Guozhong Xing, S L Huang, Kesong Yang, X L Huang, Bing Wang, Tom Wu, Lan Wang, Haitao ZhangAbstract:We demonstrate, both theoretically and experimentally, that cation vacancy can be the origin of Ferromagnetism in intrinsic dilute magnetic semiconductors. The vacancies can be controlled to tune the Ferromagnetism. Using Li-doped ZnO as an example, we found that while Li itself is nonmagnetic, it generates holes in ZnO, and its presence reduces the formation energy of Zn vacancy, and thereby stabilizes the zinc vacancy. Room temperature Ferromagnetism with p type conduction was observed in pulsed laser deposited ZnO:Li films with certain doping concentration and oxygen partial pressure.
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correlated d 0 Ferromagnetism and photoluminescence in undoped zno nanowires
Applied Physics Letters, 2010Co-Authors: Guozhong Xing, J B Yi, Jun Ding, Dandan Wang, Lili Yang, Mi He, Jinghai Yang, Tom WuAbstract:We report the correlated d(0) Ferromagnetism and photoluminescence in undoped single-crystalline ZnO nanowires synthesized by using a vapor transport method. We systematically tune the oxygen deficiency in the ZnO nanowires from 4% to 20% by adjusting the growth conditions, i.e., selecting different catalyst (Au or Ag) and varying the growth temperature. Our study suggests that oxygen vacancies induce characteristic photoluminescence and significantly boost the room-temperature Ferromagnetism. Such undoped ZnO nanowires with tunable magnetic and optical properties are promising to find applications in multifunctional spintronic and photonic nanodevices.
Jun Ding - One of the best experts on this subject based on the ideXlab platform.
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realization of single atom Ferromagnetism in graphene by cu n4 moieties anchoring
Applied Physics Letters, 2020Co-Authors: Zhongxin Liao, Jun Ding, Wen Xiao, Tongtong WangAbstract:Ferromagnetism in graphene-based materials has attracted much attention because of their potential applications in future spintronic devices. Here, we propose a strategy to induce “single-atom Ferromagnetism” in three-dimensional graphene by Cu anchoring, wherein the Cu atoms are isolated with Cu–N4 moieties, as demonstrated by extended x-ray absorption fine structure and spherical aberration correction transmission electron microscope measurements. Superconducting quantum interference device and x-ray magnetic circular dichroism measurements reveal the clear Ferromagnetism of single-atom Cu-anchored graphene with saturation magnetization of 1.15 emu/g at 2 K and 0.05 emu/g at 300 K, suggesting its promising applications in spintronics. Additionally, density functional theory (DFT) calculations prove that the Cu–N4 group can produce net magnetic moments and that the system favors the ferromagnetic stable state. More importantly, our DFT calculations show that anchoring single atoms of other transition metals can also realize single-atom Ferromagnetism in graphene.
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defect induced magnetism in undoped wide band gap oxides zinc vacancies in zno as an example
AIP Advances, 2011Co-Authors: Guozhong Xing, J B Yi, Yunhao Lu, Yufeng Tian, C C Lim, Yongfeng Li, G P Li, D Wang, B Yao, Jun DingAbstract:To shed light on the mechanism responsible for the weak Ferromagnetism in undoped wide band gap oxides, we carry out a comparative study on ZnO thin films prepared using both sol-gel and molecular beam epitaxy (MBE) methods. Compared with the MBE samples, the sol-gel derived samples show much stronger room temperature Ferromagnetism with a magnetic signal persisting up to ∼740 K, and this ferromagnetic order coexists with a high density of defects in the form of zinc vacancies. The donor-acceptor pairs associated with the zinc vacancies also cause a characteristic orange-red photoluminescence in the sol-gel films. Furthermore, the strong correlation between the Ferromagnetism and the zinc vacancies is confirmed by our first-principles density functional theory calculations, and electronic band alteration as a result of defect engineering is proposed to play the critical role in stabilizing the long-range Ferromagnetism.
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correlated d 0 Ferromagnetism and photoluminescence in undoped zno nanowires
Applied Physics Letters, 2010Co-Authors: Guozhong Xing, J B Yi, Jun Ding, Dandan Wang, Lili Yang, Mi He, Jinghai Yang, Tom WuAbstract:We report the correlated d(0) Ferromagnetism and photoluminescence in undoped single-crystalline ZnO nanowires synthesized by using a vapor transport method. We systematically tune the oxygen deficiency in the ZnO nanowires from 4% to 20% by adjusting the growth conditions, i.e., selecting different catalyst (Au or Ag) and varying the growth temperature. Our study suggests that oxygen vacancies induce characteristic photoluminescence and significantly boost the room-temperature Ferromagnetism. Such undoped ZnO nanowires with tunable magnetic and optical properties are promising to find applications in multifunctional spintronic and photonic nanodevices.
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Room Temperature Ferromagnetism in $({\hbox {Zn}}_{1-{\rm x}},{\hbox {Mg}}_{\rm x}){\hbox {O}}$ Film
IEEE Transactions on Magnetics, 2010Co-Authors: Jun Ding, Tun Seng Herng, Lap Chan, Jiabao Yi, Stella Huang, Xuelian HuangAbstract:In this work, room temperature Ferromagnetism was found in (Zn1-x, Mgx)O film with certain Mg compositions (0.06 < x < 0.50). Below the threshold composition (x < 0.06), the film shows no room temperature Ferromagnetism (RTFM) and almost no ZnO nanocrystals (NCs) were found in the film. RTF starts to appear in the (Zn0.94, Mg0.06)O film, and it becomes maximum in (Zn1-x, Mgx)O film with x = 0.20. By detailed analysis of microstructure of the film using high resolution transmission electron microscopy (HRTEM), we found that ZnO NCs were embedded in the ZnO-MgO amorphous phase. Photoluminescence (PL) results show that defects concentrations are quite high in the film. With further increment of Mg composition (x > 0.50), Ferromagnetism disappears and the film becomes fully amorphous. Besides, the defects concentration of the film is significantly reduced. The mechanism of RTFM in ZnO-MgO system may be attributed to the interaction ZnO NCs and defects surrounding them.