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41.
ZnO-based dilute magnetic semiconductors have attracted great interest for their promising application potential in spintronics. Observation of ferromagnetic-like behavior in oxides in general directs the recent focus to defect-rich undoped ZnO thin films and nanostructures. Such magnetic properties are generally mediated by the defects exclusive of magnetic ion doping, thus called defect-induced d0 ferromagnetism (FM). However the intrinsic origin of d0 FM in such materials is controversially reported. In this review we aim to locate the root of the controversy by revisiting the way how the defects were characterized and correlated with the d0 FM in each situation. We found that the main cause of controversy is rooted in a long term debate on the nature of native defects concerning the unintentional n-type conductivity in as-grown ZnO. It is particularly manifested in the assignment of the green luminescence center in photoluminescence spectra and electron paramagnetic resonance signals near g = 1.96 and g = 2.0. Only through X-ray-based microscopy and spectroscopy analysis, can the intrinsic origin of d0 FM in undoped ZnO be unambiguously attributed to the O 2p orbitals arising from zinc vacancies, rather than the Zn 3d orbitals and oxygen vacancies. In spite of the complex defect state in the nanostructures, certain parameters that influence the d0 FM in undoped ZnO systems can be extracted from various reports. Finally, we summarize the challenges and general conclusions on the d0 FM in undoped ZnO nanostructures, followed by outlooks on potential device application in spintronics. It is clear that an important step to promote d0 FM in ZnO for spintronics is to stabilize enough VZn in ZnO nanostructures, either through acceptor doping or epitaxial growth of strained films, without diminishing the crystalline quality of the structure. Future research focusing on this direction will hopefully produce new breakthrough in device applications. 相似文献
42.
Shengfu Yang Cheng Feng Daniel Spence Aula M. A. A. Al Hindawi Elspeth Latimer Andrew M. Ellis Chris Binns Davide Peddis Sarnjeet S. Dhesi Liying Zhang Yafei Zhang Kalliopi N. Trohidou Marianna Vasilakaki Nikolaos Ntallis Ian MacLaren Frank M. F. de Groot 《Advanced materials (Deerfield Beach, Fla.)》2017,29(1)
43.
Han Gyeol Lee Lingfei Wang Liang Si Xiaoyue He Daniel G. Porter Jeong Rae Kim Eun Kyo Ko Jinkwon Kim Sung Min Park Bongju Kim Andrew Thye Shen Wee Alessandro Bombardi Zhicheng Zhong Tae Won Noh 《Advanced materials (Deerfield Beach, Fla.)》2020,32(8):1905815
The metal–insulator transition (MIT) in transition-metal-oxide is fertile ground for exploring intriguing physics and potential device applications. Here, an atomic-scale MIT triggered by surface termination conversion in SrRuO3 ultrathin films is reported. Uniform and effective termination engineering at the SrRuO3(001) surface can be realized via a self-limiting water-leaching process. As the surface termination converts from SrO to RuO2, a highly insulating and nonferromagnetic phase emerges within the topmost SrRuO3 monolayer. Such a spatially confined MIT is corroborated by systematic characterizations on electrical transport, magnetism, and scanning tunneling spectroscopy. Density functional theory calculations and X-ray linear dichroism further suggest that the surface termination conversion breaks the local octahedral symmetry of the crystal field. The resultant modulation in 4d orbital occupancy stabilizes a nonferromagnetic insulating surface state. This work introduces a new paradigm to stimulate and tune exotic functionalities of oxide heterostructures with atomic precision. 相似文献
44.
Leilei Chen Rong Huang Xiaoxing Ke Jin Yu Tiantian Zhang Jean-Luc Maurice Jiheng Li Kai Li Lifeng Ni Shuzhao Huang Tiezhen Ren Zhanbing He 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(38):2301513
Parallel nanomaterials possess unique properties and show potential applications in industry. Whereas, vertically aligned 2D nanomaterials have plane orientations that are generally chaotic. Simultaneous control of their growth direction and spatial orientation for parallel nanosheets remains a big challenge. Here, a facile preparation of vertically aligned parallel nanosheet arrays of aluminum-cobalt oxide is reported via a collaborative dealloying and hydrothermal method. The parallel growth of nanosheets is attributed to the lattice-matching among the nanosheets, the buffer layer, and the substrate, which is verified by a careful transmission electron microscopy study. Furthermore, the aluminum-cobalt oxide nanosheets exhibit high-temperature ferromagnetism with a 919 K Curie temperature and a 5.22 emu g−1 saturation magnetization at 300 K, implying the potential applications in high-temperature ferromagnetic fields. 相似文献
45.
Magnetocrystalline anisotropy in the Co/Fe codoped Aurivillius oxide with different perovskite layer number
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Wen Gu Xiaoning Li Shujie Sun Liuyang Zhu Zhengping Fu Yalin Lu 《Journal of the American Ceramic Society》2018,101(6):2417-2427
Perpendicular magnetic anisotropic materials are of great interest for their huge potential to realize high‐density nonvolatile memory and logic chips. Designing such materials with lower cost and better magnetoelectric coupling still remains major challenges. In this work, aurivillius oxide ceramics with highly [00l]‐oriented grains were prepared by a facile pressureless sintering method, and the perovskite layer number was modified by varying the cobalt content. Afterwards, the unique perpendicular magnetic anisotropy and the intriguing anisotropic ferroelectric properties have been observed. The magnetic properties of the Aurivillius oxides with different layer numbers have been carefully investigated by field cooling, zero field cooling, and the magnetization with a varying field. The magnetic anisotropy in the oriented ceramics is demonstrated to be caused by the magnetocrystalline anisotropy with the easy magnetization direction along the c‐axis, which possibly arises from the unquenched 3d orbitals combined with the special layered crystal structures. The magnetocrystalline anisotropy becomes weaker in the ceramics with lower numbered perovskite layers, whereas the orientation degree of the ceramics and the ferroelectric anisotropy show quite opposite trends. Furthermore, the weak magnetoelectric coupling is also observed in the ceramics. This special anisotropic multiferroic properties may open up a new window for the Aurivillius materials. 相似文献
46.
Juan Liu Xiao Qiang Liu Xiang Ming Chen 《Journal of the American Ceramic Society》2017,100(9):4045-4057
Multiferroic ceramics were prepared and characterized in (1?x)BiFeO3–x(0.5CaTiO3–0.5SmFeO3) system by a standard solid‐state reaction process. The structure evolution was investigated by X‐ray diffraction and Raman spectrum analyses. The refinement results confirmed the different phase assemblages with varying amounts of polar rhombohedral R3c and nonpolar orthorhombic Pbnm as a function of the substitution content. In the compositions range of 0.2≤x≤0.5, polar R3c and nonpolar Pbnm coexisted, which was referred to polar‐to‐nonpolar morphotropic phase boundary (MPB). According to the dielectric and DSC analysis results, the ceramics with x≤0.2 changed to diffused ferroelectric, and the ferroelectric properties were enhanced significantly. Two dielectric relaxations were detected in the temperature range of 200‐300 K and 500‐700 K, respectively. The high‐temperature dielectric relaxation was attributed to the grain‐boundary effects. While the low temperature dielectric relaxation obtained in the samples with x=0.3‐0.5 was related to the charge transfer between Fe2+ and Fe3+. The magnetic hysteresis loops measured at different temperature indicated the enhanced magnetic properties in the present ceramics, which could be attributed to the suppressed cycloidal spin magnetic structure by Ti ions. In addition, the rare‐earth Sm spin moments might also affect the magnetic properties at relatively lower temperature. 相似文献
47.
磁记忆法对铁磁性金属构件的应力集中区域具有很好检测效果。但是,目前构件在弹性阶段和塑性阶段的磁记忆信号特征很难被区分,从而无法对构件的应力集中程度和使用寿命进行有效评估。基于固体电子理论建立了磁记忆效应的边界滑移模型,利用线性化M-T轨道算法(LMTO)计算了固体在弹性、塑性阶段,系统的能量变化、不同轨道电子的自旋态密度的变化情况,进而定量分析了构件发生屈服后的磁记忆信号变化规律。研究结果表明,应力集中程度与系统边界滑移能量呈线性正比例关系,与电子自旋态密度峰峰值、磁记忆信号呈线性反比例关系;构件发生塑性形变后,体系能量和电子自旋发生不可逆的变化,磁记忆信号曲线出现转折点;构件每发生一次塑性变形,磁记忆信号初始值都会变小,曲线斜率变小。 相似文献
48.
49.
具有宽过冷液相区的铁磁性非晶合金—铁磁性块状非晶合金的研究现状 总被引:5,自引:0,他引:5
介绍了近几年出现的具有宽过冷液相区的铁磁性非晶合金的研究状况。在传统的铁基或钴基等铁磁性非晶合金中添加Ca、Al等元素可以大大提高合金的玻璃形成能力,降低临界冷却速度,最终制备出厚度在150μm以上的块状铁磁性非晶合金。这些合金具有一些共同特点:(1)它们均为多元合金系;(2)组元之间的原子半径差别较大;(3)其晶化过程为单一阶段晶化,伴随几个晶化相的同时析出;原子的长程扩散重排导致晶化过程被大大延迟。这些合金具有一定的软磁特性,有可能作为磁性器件得到应用。 相似文献
50.
用溶胶-凝胶法制备了金红石 Ti1-xCrxO2 (x=0、0.04、0.08) 纳米粉末。磁性测量结果显示, 制备的 Cr 掺杂金红石 TiO2 纳米粉末具有室温铁磁性, 样品 x=0.04 和0.08 的饱和磁化强度Ms分别为 0.55×10-3和 1.6×10-3 emu/g, (emu/g=4π×10-7Wb•m/kg)矫顽力Hc分别为 220和 40 Oe(Oe=103/(4π)A/m)。Cr 掺杂量较大的样品的饱和磁化强度较大, 在 Ar 气中退火可以使粉末呈超顺磁性。Cr2p 区域的密集扫描 X 射线光电子能谱 (XPS)分析显示, 在所有的样品中 Cr都是以Cr3+存在。电子顺磁共振谱 (EPR)分析表明, 样品中的 Cr3+ 离子仅对其顺磁性有贡献。这些结果提示, 粉末微弱的室温铁磁性来源于掺杂引入的结构缺陷, 其中, 氧空位起重要作用。 相似文献