Particles-Matrix Bond in ZnCoO:H and ZnCoAlO:H Films: Issues of Magnetism and Spin Injection.

ZnCoO:H and ZnCoAlO:H films were synthesized by radio frequency magnetron sputtering in a (1 - x)Ar + xH2 mixed atmosphere with x = 0.2-0.5. The films contain different amounts of metallic Co particles (from 7.6% and higher) ~4-7 nm in size. The magnetic and magneto-optical (MO) behavior of the films was analyzed in combination with their structural data. The samples exhibit high values of magnetization (up to 377 emu/cm3) and MO response at room temperature. Two situations are considered: (1) the film magnetism is associated only with isolated metal particles and (2) magnetism is present both in the oxide matrix and in metal inclusions. It has been established that the formation mechanism of the magnetic structure of ZnO:Co2+ is due to the spin-polarized conduction electrons of metal particles and zinc vacancies. It was also found that in the presence of two magnetic components in the films, these components are exchange-coupled. In this case, the exchange coupling generates a high spin polarization of the films. The spin-dependent transport properties of the samples have been studied. A high value of the negative magnetoresistance of the films at room temperature (~4%) was found. This behavior was explained in terms of the giant magnetoresistance model. Thus, the ZnCoO:H and ZnCoAlO:H films with high spin polarization can be considered as sources of spin injection.

Theoretical model investigating the magnetic properties of cobalt-doped ZnO.

We propose a theoretical model to investigate the magnetic properties of cobalt-doped ZnO (ZnO:Co) thin films qualitatively. The model was built on the dilute Co dopants in the host of ZnO forming the magnetic Co+2 ions and the energy level of the magnetic ions crossing the band edge of ZnO resulting in a magnetic interaction between the Co+2 spins and the spins of the electrons from the conduction band of ZnO. The mechanism of the ferromagnetism revealed in the studied system is proposed here to be induced not only by the mediated conducting electrons via spin interactions but also by the Coulomb excitations, arising from the electrons localized by the oxygen vacancies. This approach of including Coulomb excitation in the modified carrier-mediated model could explain well the magnetic properties of ZnO:Co and solves the drawback of the carrier-mediated model in interpreting the appearance of ferromagnetism in the insulating ZnO:Co. We propose that the Coulomb excitations induced by the electrons captured by the oxygen vacancies are an essential element in the magnetic ZnO, which reveals the fact that the bound magnetic polaron model without considering the Coulomb excitation is insufficient to describe the magnetic properties of ZnO.

Theoretical investigation of Hall sign change in SrRuO3.

The appearance of Hall sign change in perovskite SrRuO3 thin films at Curie temperature was confirmed from our fabricated samples and the result was simulated by our proposed theoretical model. In particular, our simulation results are consistent with experimental results mainly due to the introduction of an impurity band in a two-band model. We found the other important factors in our theory responsible for observed consistency Hall measurements are the itinerant carrier density and its intrinsic carrier type. Eventually the theory possibly interprets the mechanism of Hall sign change.

Origin of abnormal structural transformation in a (BiPb)FeO3/SrRuO3/SrTiO3 hetero-structure probed by Rutherford backscattering.

Scientific efforts are growing to understand artificial BiFeO3/SrRuO3/SrTiO3-heterostructures, wherein an altered environment at each interface, caused by epitaxial strains, broken symmetry, off-stoichiometry and charge transfer, can generate a rich spectrum of exotic properties. Herein, (BiPb)FeO3/SrRuO3/SrTiO3-heterostructures were sputtered with various top (BiPb)FeO3-layers at different growth temperatures (T g). Strain relaxation at each interface changes with T g and generates an additional peak alongside with (BiPb)FeO3 at a high T g of 700 °C. Rutherford backscattering (RBS) was employed to understand this unusual behavior as to whether it is a mixture of two phases, layer splitting or inter-diffusion of elements. Surprisingly, complete overlapping of random and aligned RBS spectra from the sample with T g = 700 °C indicates the presence of a large amount of defects/distortions at the interfaces. The RBS compositional analysis gives clear evidence of Fe and Ru vacancies to an extent that the structural integrity may not be maintained. This abnormal condition can be explained by the inter-diffusion of Pb and Bi elements into whole films and even into the top layer of the SrTiO3 substrate, which compensates for these vacancies by substitutional replacement and is responsible for the generation of the additional SrTi(BiPb)O3-peak. Below T cSrRuO3, the magnetic properties change significantly with T g .

A facile approach to tryptophan derivatives for the total synthesis of argyrin analogues.

A facile route has been established for the synthesis of indole-substituted (S)-tryptophans from corresponding indoles, which utilizes a chiral auxiliary-facilitated Strecker amino acid synthesis strategy. The chiral auxiliary reagents evaluated were (S)-methylbenzylamine and related derivatives. To illustrate the robustness of the method, eight optically pure (S)-tryptophan analogues were synthesized, which were subsequently used for the convergent synthesis of a potent antibacterial agent, argyrin A and its analogues.

Novel MRI contrast development by lock-in suppression.

PURPOSE: The goal of this study is to develop novel MR contrast by frequency lock-in technique. METHODS: An electronic feedback device that can control the frequency and bandwidth of the feedback RF field is presented. In this study, the effects of lock-in suppressed imaging are discussed both theoretically and experimentally. RESULTS: Two important imaging experiments were performed. The first experiment used magnetizations with the same central frequency but different frequency distributions and was compared with MR images obtained with T2 contrast agents. Lock-in suppressed images showed an improvement in contrast relative to the conventional imaging method. The second experiment used magnetizations with small shifts in frequency and a broad frequency distribution. This is helpful for differentiating between small structural variations in biological tissues. The contrast achieved in in vivo tumor imaging using the lock-in suppressed technique provide higher spatial resolutions and discriminate the regimes of necrosis and activation consistent with pathologic results. CONCLUSION: Lock-in suppressed imaging introduces a conceptually new approach to MRI. Heightened sensitivity to underlying susceptibility variations and their relative contribution to total magnetization may thus be achieved to yield new and enhanced contrast.

Instrument for x-ray absorption spectroscopy with in situ electrical control characterizations.

We report a synchrotron-based setup capable of performing x-ray absorption spectroscopy and x-ray magnetic circular dichroism with simultaneous electrical control characterizations. The setup can enable research concerning electrical transport, element- and orbital-selective magnetization with an in situ fashion. It is a unique approach to the real-time change of spin-polarized electronic state of a material/device exhibiting magneto-electric responses. The performance of the setup was tested by probing the spin-polarized states of cobalt and oxygen of Zn(1-x)Co(x)O dilute magnetic semiconductor under applied voltages, both at low (~20 K) and room temperatures, and signal variations upon the change of applied voltage were clearly detected.

Biologically active constituents from the fruiting body of Taiwanofungus camphoratus.

Five new benzenoids, benzocamphorins A-E (1-5), and 10 recently isolated triterpenoids, camphoratins A-J (16-25), together with 23 known compounds including seven benzenoids (6-12), three lignans (13-15), and 13 triterpenoids (26-38) were isolated from the fruiting body of Taiwanofungus camphoratus. Their structures were established by spectroscopic analysis. Selected compounds were examined for cytotoxic and anti-inflammatory activities. Compounds 9 and 21 showed moderate cytotoxicity against MCF-7 and Hep2 cell lines with ED(50) values of 3.4 and 3.0µg/mL, respectively. Compounds 21, 25, 26, 29-31, 33, and 36 demonstrated potent anti-inflammatory activity by inhibiting lipopolysaccharide (LPS)-induced nitric oxide (NO) production with IC(50) values of 2.5, 1.6, 3.6, 0.6, 4.1, 4.2, 2.5, and 1.5µM, respectively, which were better than those of the nonspecific nitric oxide synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (l-NAME) (IC(50): 25.8µM). These results may substantiate the use of T. camphoratus in traditional Chinese medicine (TCM) for the treatment of inflammation and cancer-related diseases. The newly discovered compounds deserve further development as anti-inflammatory candidates.

Camphoratins A-J, potent cytotoxic and anti-inflammatory triterpenoids from the fruiting body of Taiwanofungus camphoratus.

Ten new triterpenoids, camphoratins A-J (1-10), along with 12 known compounds were isolated from the fruiting body of Taiwanofungus camphoratus. Their structures were established by spectroscopic analysis and chemical methods. Compound 10 is the first example of a naturally occurring ergosteroid with an unusual cis-C/D ring junction. Compounds 2-6 and 11 showed moderate to potent cytotoxicity, with EC(50) values ranging from 0.3 to 3 µM against KB and KB-VIN human cancer cell lines. Compounds 6, 10, 11, 14-16, 18, and 21 exhibited anti-inflammatory NO-production inhibition activity with IC(50) values of less than 5 µM, and were more potent than the nonspecific NOS inhibitor N(ω)-nitro-L-arginine methyl ester.

Short range magnetic correlations induced by La substitution in Ho(1-x)La(x)Mn(2)O(5).

Magnetic susceptibility, x-ray diffraction, neutron diffraction and Raman scattering measurements are employed to study the effects of La substitution on the magnetic properties of multiferroic HoMn(2)O(5). 9% and 18% La-substituted compounds crystallize into the same orthorhombic Pbam symmetry as the parent compound. The magnetic responses to an ac driving magnetic field between 40 and 140 K are greatly enhanced by 18% La substitution. The neutron magnetic diffraction patterns reveal the development of short range magnetic correlations below 140 K. In addition, two Raman peaks and a series of new x-ray diffraction peaks suddenly develop below this temperature. Incommensurate long range antiferromagnetic order appears below 38 K. Magnetic frustration could be the main mechanism governing the present observations.