skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Intrinsic ferromagnetic coupling in Co{sub 3}O{sub 4} quantum dots activatedby graphene hybridization

Abstract

Activating ferromagnetic couplings of transition-metallic ions in the antiferromagnetic metal oxide semiconductors is desired for creating ferromagnetic semiconductors for spintronics applications. Here, we report intrinsic ferromagnetic coupling in a typical antiferromagnetic metal oxide Co{sub 3}O{sub 4}, by virtue of a hybrid structure that modifies the valence state of Co ions. The Co{sub 3}O{sub 4} quantum dots exhibit ferromagnetism of 2.2 emu/g at 2 K after hybridization with reduced graphene oxide (RGO). In this hybrid structure, electron-transfer from RGO to Co{sub 3}O{sub 4} occurs and Co{sup 3+} ions occupying the octahedral (O{sub h}) positions are converted into Co{sup 2+}. Then the super-exchange interactions between Co{sup 2+} ions at T{sub d} (tetrahedral) and O{sub h} positions switch the magnetic coupling of Co{sup 2+}(T{sub d})–Co{sup 2+}(T{sub d}) from antiferromagnetic to ferromagnetic. These results offer promise for tailoring the spin exchange interactions of oxide semiconductors for spintronics applications.

Authors:
; ; ; ; ; ;  [1]; ; ;  [1];  [2]
  1. National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, Anhui (China)
  2. (China)
Publication Date:
OSTI Identifier:
22590818
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 108; Journal Issue: 25; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANTIFERROMAGNETISM; COBALT IONS; COBALT OXIDES; COUPLINGS; EXCHANGE INTERACTIONS; GRAPHENE; METALS; QUANTUM DOTS; SEMICONDUCTOR MATERIALS; SPIN EXCHANGE; VALENCE

Citation Formats

Chen, Lin, Hu, Fengchun, Duan, Hengli, Liu, Qinghua, Tan, Hao, Yao, Tao, Sun, Zhihu, E-mail: ywsh2000@ustc.edu.cn, E-mail: zhsun@ustc.edu.cn, Yan, Wensheng, E-mail: ywsh2000@ustc.edu.cn, E-mail: zhsun@ustc.edu.cn, Jiang, Yong, Wei, Shiqiang, and Hefei Science Center, Chinese Academy of Sciences, Hefei 230029. Intrinsic ferromagnetic coupling in Co{sub 3}O{sub 4} quantum dots activatedby graphene hybridization. United States: N. p., 2016. Web. doi:10.1063/1.4954715.
Chen, Lin, Hu, Fengchun, Duan, Hengli, Liu, Qinghua, Tan, Hao, Yao, Tao, Sun, Zhihu, E-mail: ywsh2000@ustc.edu.cn, E-mail: zhsun@ustc.edu.cn, Yan, Wensheng, E-mail: ywsh2000@ustc.edu.cn, E-mail: zhsun@ustc.edu.cn, Jiang, Yong, Wei, Shiqiang, & Hefei Science Center, Chinese Academy of Sciences, Hefei 230029. Intrinsic ferromagnetic coupling in Co{sub 3}O{sub 4} quantum dots activatedby graphene hybridization. United States. doi:10.1063/1.4954715.
Chen, Lin, Hu, Fengchun, Duan, Hengli, Liu, Qinghua, Tan, Hao, Yao, Tao, Sun, Zhihu, E-mail: ywsh2000@ustc.edu.cn, E-mail: zhsun@ustc.edu.cn, Yan, Wensheng, E-mail: ywsh2000@ustc.edu.cn, E-mail: zhsun@ustc.edu.cn, Jiang, Yong, Wei, Shiqiang, and Hefei Science Center, Chinese Academy of Sciences, Hefei 230029. 2016. "Intrinsic ferromagnetic coupling in Co{sub 3}O{sub 4} quantum dots activatedby graphene hybridization". United States. doi:10.1063/1.4954715.
@article{osti_22590818,
title = {Intrinsic ferromagnetic coupling in Co{sub 3}O{sub 4} quantum dots activatedby graphene hybridization},
author = {Chen, Lin and Hu, Fengchun and Duan, Hengli and Liu, Qinghua and Tan, Hao and Yao, Tao and Sun, Zhihu, E-mail: ywsh2000@ustc.edu.cn, E-mail: zhsun@ustc.edu.cn and Yan, Wensheng, E-mail: ywsh2000@ustc.edu.cn, E-mail: zhsun@ustc.edu.cn and Jiang, Yong and Wei, Shiqiang and Hefei Science Center, Chinese Academy of Sciences, Hefei 230029},
abstractNote = {Activating ferromagnetic couplings of transition-metallic ions in the antiferromagnetic metal oxide semiconductors is desired for creating ferromagnetic semiconductors for spintronics applications. Here, we report intrinsic ferromagnetic coupling in a typical antiferromagnetic metal oxide Co{sub 3}O{sub 4}, by virtue of a hybrid structure that modifies the valence state of Co ions. The Co{sub 3}O{sub 4} quantum dots exhibit ferromagnetism of 2.2 emu/g at 2 K after hybridization with reduced graphene oxide (RGO). In this hybrid structure, electron-transfer from RGO to Co{sub 3}O{sub 4} occurs and Co{sup 3+} ions occupying the octahedral (O{sub h}) positions are converted into Co{sup 2+}. Then the super-exchange interactions between Co{sup 2+} ions at T{sub d} (tetrahedral) and O{sub h} positions switch the magnetic coupling of Co{sup 2+}(T{sub d})–Co{sup 2+}(T{sub d}) from antiferromagnetic to ferromagnetic. These results offer promise for tailoring the spin exchange interactions of oxide semiconductors for spintronics applications.},
doi = {10.1063/1.4954715},
journal = {Applied Physics Letters},
number = 25,
volume = 108,
place = {United States},
year = 2016,
month = 6
}
  • In this letter, we report on the high frequency (239.2 and 336 GHz) electron spin resonance (ESR) studies performed on graphene quantum dots (GQDs), prepared through a wet chemistry route from three types of coal: (a) bituminous, (b) anthracite, and (c) coke; and from non-coal derived GQDs. The microwave frequency-, power-, and temperature-dependent ESR spectra coupled with computer-aided simulations reveal four distinct magnetic defect centers. In bituminous- and anthracite-derived GQDs, we have identified two of them as intrinsic carbon-centered magnetic defect centers (a broad signal of peak to peak width = 697 (10{sup −4} T), g = 2.0023; and a narrow signal of peak tomore » peak width = 60 (10{sup −4} T), g = 2.003). The third defect center is Mn{sup 2+} ({sup 6}S{sub 5/2}, 3d{sup 5}) (signal width = 61 (10{sup −4} T), g = 2.0023, A{sub iso} = 93(10{sup −4} T)), and the fourth defect is identified as Cu{sup 2+} ({sup 2}D{sub 5/2}, 3d{sup 9}) (g{sub ⊥} = 2.048 and g{sub ‖} = 2.279), previously undetected. Coke-derived and non-coal derived GQDs show Mn{sup 2+} and two-carbon related signals, and no Cu{sup 2+} signal. The extrinsic impurities most likely originate from the starting coal. Furthermore, Raman, photoluminescence, and ESR measurements detected no noticeable changes in the properties of the bituminous GQDs after one year. This study highlights the importance of employing high frequency ESR spectroscopy in identifying the (magnetic) defects, which are roadblocks for spin relaxation times of graphene-based materials. These defects would not have been possible to probe by other spin transport measurements.« less
  • Monolayer graphene oxide quantum dots (GOQDs) were obtained by oxidative cutting. The magnetic properties of GOQDs were studied. The results show that most of GOQDs are nonmagnetic, and only few of GOQDs are weakly paramagnetic. The ratio of magnetic GOQDs with the average diameter of 4.13, 3.3, and 1.67 nm is 1/14, 1/15, and 1/70, respectively. It is proposed that the edge states magnetism is suppressed by the edge defects and/or the magnetic correlation induced spins cancellation between magnetic fragments of the boundary, and hydroxyl groups on the basal plane are the major magnetic source of magnetic GOQDs.
  • Using first-principles calculations, we have investigated the electronic and magnetic properties of zigzag graphene-like carbon-nitride nanoribbons (Zg-CNNRs) with mono- and dihydrogen-terminated edges asymmetrically. The results demonstrate that spin-down channel completely dominates the states adjacent Fermi level, which is an intrinsic feature and can be accounted for the valence band maximum derived from the nonbonding N-(p{sub x},p{sub y}) orbitals, instead of the bonding C/N-p{sub z} π state. Importantly, ferromagnetic ordering is found to be preferred and the magnetism is entirely localized on the N sites of saturated edge due to its stronger electronegativity. Additionally, various edge saturations are further proposed tomore » try to enhance the ferromagnetic ordering and to manipulate the magnetism distributions of Zg-CNNRs.« less
  • This paper investigates how chemical dopants affect the electronic properties of CdSe quantum dots (QDs) and why a model that incorporates the concepts of orbital hybridization must be used to understand these properties. Extended X-ray absorption fine structure spectroscopy measurements show that copper dopants in CdSe QDs occur primarily through a statistical doping mechanism. Ultraviolet photoemission spectroscopy (UPS) experiments provide a detailed insight on the valence band (VB) structure of doped and undoped QDs. Using UPS measurements, we are able to observe photoemission from the Cu d-levels above VB maximum of the QDs which allows a complete picture of themore » energy band landscape of these materials. This information provides insights into many of the physical properties of doped QDs, including the highly debated near-infrared photoluminescence in Cu doped CdSe QDs. We show that all our results point to a common theme of orbital hybridization in Cu doped CdSe QDs which leads to optically and electronically active states below the conduction band minimum. Our model is supported from current–voltage measurements of doped and undoped materials, which exhibit Schottky to Ohmic behavior with Cu doping, suggestive of a tuning of the lowest energy states near the Fermi level.« less
  • We report enhanced sensitization of silicon through nonradiative energy transfer (NRET) of the excitons in an energy-gradient structure composed of a cascaded bilayer of green- and red-emitting CdTe quantum dots (QDs) on bulk silicon. Here NRET dynamics were systematically investigated comparatively for the cascaded energy-gradient and mono-dispersed QD structures at room temperature. We show experimentally that NRET from the QD layer into silicon is enhanced by 40% in the case of an energy-gradient cascaded structure as compared to the mono-dispersed structures, which is in agreement with the theoretical analysis based on the excited state population-depopulation dynamics of the QDs.