Structure of Co-Doped Alq3 thin films investigated by grazing incidence X-ray absorption fine structure and Fourier transform infrared spectroscopy

The structural properties of Co-doped tris(8-hydroxyquinoline)aluminum (Alq(3)) have been studied by grazing incidence X-ray absorption fine structure (GIXAFS) and Fourier transform infrared spectroscopy (FTIR). GIXAFS analysis suggests that there are multivalent Co-Alq(3) complexes and the doped Co atoms tend to locate at the attraction center with respect to N and O atoms and bond with them. The FTIR spectra indicate that the Co atoms interact with the meridional (mer) isomer of Alq(3) rather than forming inorganic compounds.     

Honeycomb layer of cobalt(II) azide hydrazine showing weak ferromagnetism

Using hydrazine (N2H4) as a cobridge with azide, a honeycomb-layered cobalt(II) coordination polymer, Co(N2H4)(N3)2 (1), is obtained that exhibits spin-canted weak ferromagnetism with TN of 13.5 K.     

Facilely synthesized N-doped graphene sheets and its ferromagnetic origin

Inducing ferromagnetism into graphene is vital today because it has a wide range of applications such as spintronics devices and magnetic memory devices. In this paper, we will report a new method to synthesize ferromagnetic graphene by nitrogen doping. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were utilized to testify the N-doped material and further discuss the N-doped process. The superconducting quantum interference device (SQUID) was put in and used to analyze the magnetic properties of the N-doped graphene sheets. It shows that the material exhibits ferromagnetism at both 3 K and 300 K and the ferromagnetic saturation moment is 0.412 emu/g and 0.051 emu/g, respectively. The mechanism of the origin of the ferromagnetism in N-doped graphene sheets will also be discussed in this paper. It shows that, when the amount graphitic N reached the threshold, the origin of the ferromagnetism will change from defects induced by nitrogen atoms to the transition in energy band caused by graphitic N.     

Sol–Gel Synthesis and Magnetic Studies of Titanium Dioxide Doped with 10% M (M=Fe,Mn and Ni)

TiO₂ nanocrystals doped with 1%, 5% and 10% Co/TiO₂ and 10% M (M=Fe, Mn and Ni) were prepared by the sol–gel technique and characterized using X-ray diffraction and SQUID. The as-prepared samples are found to be paramagnetic at room temperature, with the magnetic susceptibility following the Curie–Weiss law in the investigated range of 2–370 K. However, transformation from paramagnetism to room-temperature ferromagnetism (RTFM) for the 5% Co/TiO₂ was observed by hydrogenating the sample at 573 K while the 1% sample remained paramagnetic. As the percentage of Co was increased from 5% to 10% the Curie temperature increased from 390 K to 470 K determined via extrapolation. Transformation from paramagnetism to room-temperature ferromagnetism (RTFM) was also observed by hydrogenation of 10% Fe/TiO₂ at 573 K for 6 h. X-ray diffraction of the hydrogenated sample shows only single phase TiO₂ structure suggesting that the observed RTFM may be intrinsic but magnetic studies may suggest the possibility of Fe nanoparticles.     

Dual Manipulation of Ferromagnetism in Co-Doped ZnO Thin Films by Surfactant and n-Type Carriers

We present a conceptually-new approach “dual manipulation effect” using the surfactant passivation and the electron carrier doping for mediating intrinsic ferromagnetism in Codoped ZnO dilute magnetic semiconductor (DMS) thin films. The first-principles calculations show that the surface passivation by hydrogen serves as a magnetism switch for the Co-O-Co magnetic coupling at the surface of the thin film, and thus can control the spin polarization of the doped Co atoms. Meanwhile, the electron carrier doping can further function as an effective layerlike ferromagnetism mediator for the underneath layer. The dual manipulation effect sheds light on the essential magnetism origin of n-type Co:ZnO DMS thin films, and may be used as an alternative strategy for enhancing the ferromagnetism in other n-type DMS oxides thin films.     

Construction of hydrogen-bonded and coordination-bonded networks of cobalt(II) with pyromellitate: synthesis,structures, and magnetic properties

Synthesis (hydrothermal and metathesis), characterization (UV-vis, IR, TG/DTA), single-crystal X-ray structures, and magnetic properties of three cobalt(II)-pyromellitate complexes, purple [Co(2)(pm)](n) (1), red [Co(2)(pm)(H(2)O)(4)](n) x 2nH(2)O (2), and pink [Co(H(2)O)(6)](H(2)pm) (3) (H(4)pm = pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid)), are described. 1 consists of one-dimensional chains of edge-sharing CoO(6) octahedra that are connected into layers via O-C-O bridges. The layers are held together by the pyromellitate (pm(4-)) backbone to give a three-dimensional structure, each ligand participating in an unprecedented 12 coordination bonds (Co-O) to 10 cobalt atoms. 2 consists of a three-dimensional coordination network possessing cavities in which unbound water molecules reside. This highly symmetric network comprises eight coordinate bonds (Co-O) between oxygen atoms of pm(4-) to six trans-Co(H(2)O)(2). 3 possesses a hydrogen-bonded sandwich structure associating layers of [Co(H(2)O)(6)](2+) and planar H(2)pm(2-). The IR spectra, reflecting the different coordination modes and charges of the pyromellitate, are presented and discussed. The magnetic properties of 1 indicate complex behavior with three ground states (collinear and canted antiferromagnetism and field-induced ferromagnetism). Above the Néel temperature (T(N)) of 16 K it displays paramagnetism with short-range ferromagnetic interactions (Theta = +16.4 K, mu(eff) = 4.90 mu(B) per Co). Below T(N) a weak spontaneous magnetization is observed at 12.8 K in low applied fields (H < 100 Oe). At higher fields (H > 1000 Oe) metamagnetic behavior is observed. Two types of hysteresis loops are observed; one centered about zero field and the second about the metamagnetic critical field. The critical field and the hysteresis width increase as the temperature is lowered. The heat capacity data suggest that 1 has a 2D or 3D magnetic lattice, and the derived magnetic entropy data confirm an anisotropic s(eff) = 1/2 for the cobalt(II) ion. Magnetic susceptibility data indicate that 2 and 3 are paramagnets.     

Strong room-temperature ferromagnetism in Co2+-doped TiO2 made from colloidal nanocrystals

Colloidal cobalt-doped TiO(2) (anatase) nanocrystals were synthesized and studied by electronic absorption, magnetic circular dichroism, transmission electron microscopy, magnetic susceptibility, cobalt K-shell X-ray absorption spectroscopy, and extended X-ray absorption fine structure measurements. The nanocrystals were paramagnetic when isolated by surface-passivating ligands, weakly ferromagnetic (M(s) approximately 1.5 x 10(-)(3) micro(B)/Co(2+) at 300 K) when aggregated, and strongly ferromagnetic (up to M(s) = 1.9 micro(B)/Co(2+) at 300 K) when spin-coated into nanocrystalline films. X-ray absorption data reveal that cobalt is in the Co(2+) oxidation state in all samples. In addition to providing strong experimental support for the existence of intrinsic ferromagnetism in cobalt-doped TiO(2), these results demonstrate the possibility of using colloidal TiO(2) diluted magnetic semiconductor nanocrystals as building blocks for assembly of ferromagnetic semiconductor nanostructures with potential spintronics applications.     

Structure of the active sites of Co-Mo Hydrodesulfurization catalysts as studied by magnetic susceptibility measurement and NO adsorption

The elucidation of a molecular structure of the active sites (i.e., the Co-Mo-S phase) of Co-Mo hydrodesulfurization catalysts has received extensive attention. In the present study, we unambiguously determined, for the first time, the NO adsorption behavior and magnetic property of the Co-Mo-S phase by preparing unique Co-Mo/Al(2)O(3) catalysts (CVD-Co/MoS(2)/Al(2)O(3)), in which all the Co atoms are present as the Co-Mo-S phase. The catalysts were characterized by NO adsorption (pulse technique and FTIR), Co K-edge XANES, and the magnetic susceptibility and effective magnetic moment of Co. Nitric oxide molecules were adsorbed on 33% of the Co atoms in CVD-Co/MoS(2)/Al(2)O(3) after sulfidation and on only half of the Co atoms even after an H(2)-treatment of the sulfided catalyst at 573-673 K. The Co atoms in CVD-Co/MoS(2)/Al(2)O(3) exclusively exhibited an antiferromagnetic property, indicating that even-numbered Co atoms are interacting with each other in the Co-Mo-S phase. A Co-Mo/Al(2)O(3) catalyst, prepared by a conventional impregnation technique, was composed of the antiferromagnetic Co sulfide species as observed in CVD-Co/MoS(2)/Al(2)O(3) in addition to Co(9)S(8). On the basis of the NO adsorption behavior and magnetic property, it is empirically proposed that the structure of the Co-Mo-S phase is represented as a Co sulfide dinuclear cluster located on the edge of MoS(2) particles. The magnetic property of Co/Al(2)O(3) sulfide catalysts depended on the preparation method.     

Comparative electronic band structure study of the intrachain ferromagnetic versus antiferromagnetic coupling in the magnetic oxides Ca3Co2O6 and Ca3FeRhO6

In the (MM'O6)infinity chains of the transition-metal magnetic oxides Ca3MM'O6 the MO6 trigonal prisms alternate with the M'O6 octahedra by sharing their triangular faces. In the (Co(2O6)infinity chains of Ca3Co2O6 (M = M' = Co) the spins are coupled ferromagnetically, but in the (FeRhO6)infinity chains of Ca3FeRhO6 (M = Fe, M' = Rh) they are coupled antiferromagnetically. The origin of this difference was probed by carrying out spin-polarized density functional theory electronic band structure calculations for ordered spin states of Ca3Co2O6 and Ca3FeRhO6. The spin state of a (MM'O6)infinity chain determines the occurrence of direct metal-metal bonding between the adjacent trigonal prism and octahedral site transition-metal atoms. The extent of direct metal-metal bonding in the (Co2O6)infinity chains of Ca3Co2O6 is stronger in the intrachain ferromagnetic state than in the intrachain antiferromagnetic state, so that the intrachain ferromagnetic state becomes more stable than the intrachain antiferromagnetic state. Such a metal-metal-bonding-induced ferromagnetism is expected to occur in magnetic insulators and magnetic metals of transition-metal elements in which direct metal-metal bonding can be enhanced by ferromagnetic ordering. In the (FeRhO6)infinity chains of Ca3FeRhO6 the ferromagnetic coupling does not lead to a strong metal-metal bonding and the adjacent spins interact by the Fe-O...O-Fe super-superexchange, hence leading to an antiferromagnetic coupling.     

Magnetische Messungen anHeusler-Phasen (Co,Mn)2 XY (X=Ti,Zr,Hf und Mn;Y=Ge und Sn)

Magnetic measurements onHeusler alloys (Co,Mn)₂ XY have been performed. With a few exceptions there is no enhancement of ferromagnetism while substituting cobalt by manganese. The results can be explained by a partially antiferromagnetic ordering of the manganese atoms.     

八-羟基喹啉铝薄膜光致发光的厚度依赖性质

In situ thickness dependent photoluminescence (PL) measurements of tris(8-hydroxyquinoline) aluminum(Alq3) film were performed. At the beginning of Alq3 deposition on the glass substrate, the Alq3 emission showed a sharp red-shift. Further deposition of Alq3 resulted slight red-shift, and finally tended to saturated value. The total red-shift of about 12 nm was observed for the Alq3 film thickness range from 2 to 500 nm.This red-shift was attributed to the change from the 2D to 3D exciton state with increasing Alq3 film thickness. Meanwhile, the PL intensity of Alq3 emission increased continuously, and showed a rate change at the initial deposition of Alq3 due to non-rediative decay of excitons arised from the interaction between excitons and the substrate, and finally tended to saturation with the Alq3 thickness.     

1D and 2D end-to-end azide-bridged cobalt(II) complexes: syntheses, crystal structures, and magnetic properties

Two new polynuclear azido-bridged Co(II) compounds with formulas catena-[Co(mu1,3-N3)(N3)(py)2(H2O)]n (1) and [Co(mu1,3-N3)2(4-acpy)2]n (2) (py=pyridine, 4-acpy=4-acetylpyridine) have been structurally and magnetically characterized. Compound 1 crystallizes in the orthorhombic system Fddd space group and consists of a single end-to-end azido-bridged chain with the Co(II) atoms in a CoN5O slightly distorted octahedron. Compound 2 crystallizes in the monoclinic system P21/a space group and shows 2D sheets built up through end-to-end azido bridges with the Co(II) atoms in a CoN6 environment. The magnetic properties of 1 and 2 are reported. In the high-temperature region, the plots of chiM or chiMT vs T for 1 and 2 compounds can be fitted by using the Curie-Weiss law, and the best-fit values are -69.1 and -22.6 K, respectively. For 2 magnetic ordering and spontaneous magnetization is achieved below Tc=25 K.     

超薄层在白色有机电致发光器件中的应用

以DCJTB为掺杂剂, 以BCP为空穴阻挡层, 研究了两种结构的有机电致发光器件ITO/NPB/BCP/Alq3:DCJTB/Alq3/Al(结构A)和ITO/NPB/BCP/Alq3/Alq3:DCJTB/Alq3/Al(结构B)的电致发光光谱. 实验结果显示, 在结构A器件的电致发光光谱中, 绿光的相对发光强度较弱,增加Alq3层的厚度对绿光的相对发光强度的影响也很小; 而在结构B器件的电致发光光谱中, BCP层与掺杂层(Alq3:DCJTB)之间的Alq3薄层对绿光的相对发光强度影响显著, 用很薄的Alq3层就可以得到强的绿光发射. 进一步改变器件结构, 利用有机超薄层就可以得到稳定的白光器件ITO/NPB(50 nm)/BCP(3 nm)/Alq3(3 nm)/Alq3:DCJTB(1%(w))(5 nm)/Alq3(7 nm)/Al. 随着电压的增加(14-18 V), 该器件的色坐标基本保持在(0.33, 0.37)处不动; 在432 mA·cm-2的电流密度下, 该器件的发光亮度可达11521 cd·m-2.     

Fluorinated Alq3 derivatives with tunable optical properties

This communication reports that not only the emission colour but also the photoluminescence quantum yield of Alq3 can be tuned by introducing fluorine atoms at different positions; with fluorination at C-5 the emission is red-shifted with a tremendously decreased intensity, fluorination at C-6 causes a blue-shift with a significantly increased intensity, and fluorination at C-7 has a minor effect on both the colour and intensity of Alq3's emission.     

Interface modification of 8-hydroxyquinoline aluminium with combined effects in quasi-solid dye-sensitized solar cells

In this paper, 8-hydroxyquinoline aluminium (Alq(3)) was used in interface modification of dye-sensitized solar cells (DSCs). Alq(3) was the first discovered interface modification material with combined effects of retarding charge recombination and F?rster resonant energy transfer (FRET). Results of dark current curve and AC impedance showed that Alq(3) could retard charge recombination in DSCs. I-V curves showed that conversion efficiency increased with Alq(3) modification. Besides the interface modification effect, it was discovered that Alq(3) also acted as energy relay dye with the FRET effect between itself and N3, which increased photoresponse and electron injection. The application of Alq(3) with combined effects opened a new door to explore more novel multi-functional interface modification materials to improve the performance of DSCs.     

The Orbital Origins of Magnetism: From Atoms to Molecules to Ferromagnetic Alloys

A chemical view of spin magnetic phenomena in finite (atoms and molecules) and infinite (transition metals and their alloys) systems using the concepts of bonding and electronic shielding is presented. The concept is intended to serve as a semiquantitative signpost for the synthesis of new ferromagnets. After a concise overview of the historic development of related theories developed within the physics community, the consequences of spin-spin coupling (made manifest in the exchange or Fermi hole) in atoms and molecules are explored. Upon moving to a paramagnetic state, the majority/minority spin species become more/less tightly bound to the nucleus, resulting in differences in the energies and spatial extents of the two sets of spin orbitals. By extrapolating well-known arguments from ligand-field theory, the paucity of ferromagnetic transition metals arises from quenching the paramagnetism of the free atoms due to strong interatomic interactions in the solid state. Critical valence electron concentrations in Fe, Co, and Ni, however, result in local electronic instabilities due to the population of antibonding states at the Fermi level varepsilon(F). Removal of these antibonding states from the vicinity of varepsilon(F) is the origin of ferromagnetism; in the pure metals this results in strengthening the chemical bonds. In the 4d and 5d transition metals, the valence d orbitals are too well shielded from the nucleus, so a transition to a ferromagnetic state does not result in sufficiently large changes to occur. Thus, the exceptional occurence of ferromagnetism only in the first transition series appears to parallel the special main-group chemistry of the first long period. A connection between ferromagnetism in the transition metals and Pearson's absolute hardness eta is easily established and shows that ferromagnetism appears only when eta<0.2 eV in the nonmagnetic calculation. As expected from the principle of maximum hardness, Fe, Co, and Ni all become harder upon moving to the more stable ferromagnetic state. Magnetism in intermetallic alloys follows the same path. Whether or not an alloy contains ferromagnetic elements, the presence of antibonding states at varepsilon(F) serves as a "fingerprint" to indicate a ferromagnetic instability. The differences in the sizes of the local magnetic moments on the constituent atoms of a ferromagnetic alloy can be understood in terms of the relative contributions to the density of states at varepsilon(F) in the nonmagnetic calculations. Appropriately parameterized, nonmagnetic, semi-empirical calculations can also be used to expose the ferromagnetic instability in elements and alloys. These techniques, which have become relatively commonplace, can be used to guide the synthetic chemist in search of new ferromagnetic materials.     

Novel pyridazine based scorpionate ligands in cobalt and nickel boratrane compounds

Heating of 6-methylpyridazine-3-thione (HPn(Me)) and 6-tert-butylpyridazine-3-thione (HPn(tBu)) with potassium borohydride in diphenylmethane in a 3:1 ratio gave two new scorpionate ligands K[HB(Pn(Me))(3)] and K[HB(Pn(tBu))(3)]. Single crystal X-ray diffraction analysis of the methyl derivative K[HB(Pn(Me))(3)] revealed a dimeric species with one potassium atom coordinated by six sulfur atoms of two scorpionate ligands and a second potassium atom coordinated by three nitrogen atoms of one of the two ligands as well as by three water molecules. The reaction of K[HB(Pn(tBu))(3)] with nickel(II) chloride or cobalt(II) chloride in CH(2)Cl(2) led to the new boratrane compounds [M{B(Pn(tBu))(3)}Cl] (M = Ni 1, Co 3) where a formal reduction of the metal ions to Ni(I) and Co(I), respectively, and activation of the B-H bond occurred. Similar reactivity was observed by employing K[HB(Pn(R))(3)] (R = Me, tBu) and nickel(II) chloride in water. Reaction with cobalt(II) chloride in water also gave boratrane compounds [Co{B(Pn(R))(3)}(Pn(R))] (R = tBu 4, Ph 5), but instead of a chloride a bidentate pyridazinethionate ligand from a defragmentated scorpionate is found in the molecules. The molecular structures of all nickel and cobalt compounds were determined by single crystal X-ray diffraction analyses confirming the formation of boratranes in compounds 1-5. Magnetic measurements confirm the reduced oxidation states and the paramagnetic character of the Ni(I) and Co(I) complexes. Supportive DFT studies were carried out for a better understanding of the electronic nature of the metal-boron bond of the boratrane complexes.     

Evidence of superparamagnetic co clusters in pulsed laser deposition-grown Zn0.9Co0.1O thin films using atom probe tomography

Nanosized Co clusters (of about 3 nm size) were unambiguously identified in Co-doped ZnO thin films by atom probe tomography. These clusters are directly correlated to the superparamagnetic relaxation observed by ZFC/FC magnetization measurements. These analyses provide strong evidence that the room-temperature ferromagnetism observed in the magnetization curves cannot be attributed to the observed Co clusters. Because there is no experimental evidence of the presence of other secondary phases, our results reinforce the assumption of a defect-induced ferromagnetism in Co-doped ZnO diluted magnetic semiconductors.     

Synthesis and Magnetic Properties of Co3O4 Nanoflowers

Co3O4 nanoflowers were prepared through a sequential process of a hydrothermal reaction and heat treatment. The as-synthesized products were characterized by powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and infrared spectrum. These nanoflowers consist of numerous Co3O4 nanofibers, which have diameters of 20-40 nm, and lengths ranging from 100 nm to 500 nm. They have pore structures and Brunauer-Emmett-Teller surface area of ?34.61 m2/g. The temperature dependence curves of magnetization in zero-field-cooled conditions and field-cooled indicate mainly antiferromagnetism and weak ferromagnetism of Co3O4 nanoflowers at blocking temperature of ?34 K respectively.