181 research outputs found
Magnetic Properties of Pr0.7Ca0.3MnO3/SrRuO3 Superlattices
High-quality Pr0.7Ca0.3MnO3/SrRuO3 superlattices were fabricated by pulsed
laser deposition and were investigated by high-resolution transmission electron
microscopy and SQUID magnetometry. Superlattices with orthorhombic and
tetragonal SrRuO3 layers were investigated. The superlattices grew coherently;
in the growth direction Pr0.7Ca0.3MnO3 layers were terminated by MnO2- and
SrRuO3 layers by RuO2-planes. All superlattices showed antiferromagnetic
interlayer coupling in low magnetic fields. The coupling strength was
significantly higher for orthorhombic than for tetragonal symmetry of the
SrRuO3 layers. The strong interlayer exchange coupling in the superlattice with
orthorhombic SrRuO3 layers led to a magnetization reversal mechanism with a
partially inverted hysteresis loop.Comment: 12 pages, 4 figure
Orthorhombic to tetragonal transition of SrRuO3 layers in Pr0.7Ca0.3MnO3/SrRuO3 superlattices
High-quality Pr0.7Ca0.3MnO3/SrRuO3 superlattices with ultrathin layers were
fabricated by pulsed laser deposition on SrTiO3 substrates. The superlattices
were studied by atomically resolved scanning transmission electron microscopy,
high-resolution transmission electron microscopy, resistivity and
magnetoresistance measurements. The superlattices grew coherently without
growth defects. Viewed along the growth direction, SrRuO3 and Pr0.7Ca0.3MnO3
layers were terminated by RuO2 and MnO2, respectively, which imposes a unique
structure to their interfaces. Superlattices with a constant thickness of the
SrRuO3 layers, but varying thickness of the Pr0.7Ca0.3MnO3 layers showed a
change of crystalline symmetry of the SrRuO3 layers. At a low Pr0.7Ca0.3MnO3
layer thickness of 1.5 nm transmission electron microscopy proved the SrRuO3
layers to be orthorhombic, whereas these were non-orthorhombic for a
Pr0.7Ca0.3MnO3 layer thickness of 4.0 nm. Angular magnetoresistance
measurements showed orthorhombic (with small monoclinic distortion) symmetry in
the first case and tetragonal symmetry of the SrRuO3 layers in the second case.
Mechanisms driving this orthorhombic to tetragonal transition are briefly
discussed.Comment: 23 pages, 12 figure
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On the electronic properties of a single dislocation
A detailed knowledge of the electronic properties of individual dislocations is necessary for next generation nanodevices. Dislocations are fundamental crystal defects controlling the growth of different nanostructures (nanowires) or appear during device processing. We present a method to record electric properties of single dislocations in thin silicon layers. Results of measurements on single screw dislocations are shown for the first time. Assuming a cross-section area of the dislocation core of about 1 nm2, the current density through a single dislocation is J = 3.8 Ă 1012 A/cm2 corresponding to a resistivity of Ï â
1 à 10-8 Ω cm. This is about eight orders of magnitude lower than the surrounding silicon matrix. The reason of the supermetallic behavior is the high strain in the cores of the dissociated dislocations modifying the local band structure resulting in high conductive carrier channels along defect cores
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Single-electron transitions in one-dimensional native nanostructures
Low-temperature measurements proved the existence of a two-dimensional electron gas at defined dislocation arrays in silicon. As a consequence, single-electron transitions (Coulomb blockades) are observed. It is shown that the high strain at dislocation cores modifies the band structure and results in the formation of quantum wells along dislocation lines. This causes quantization of energy levels inducing the formation of Coulomb blockades
Crystal structure of cleaved vaspin (serpinA12)
The adipokine vaspin (serpinA12) is mainly expressed in white adipose tissue and exhibits various beneficial effects on obesity-related processes. Kallikrein 7 is the only known target protease of vaspin and is inhibited by the classical serpin inhibitory mechanism involving a cleavage of the reactive center loop between P1 (M378) and P1âČ (E379). Here, we present the X-ray structure of vaspin, cleaved between M378 and E379. We provide a comprehensive analysis of differences between the uncleaved and cleaved forms in the shutter, breach, and hinge regions with relation to common molecular features underlying the serpin inhibitory mode. Furthermore, we point out differences towards other serpins and provide novel data underlining the remarkable stability of vaspin. We speculate that the previously reported FKGx1Wx2x3 motif in the breach region may play a decisive role in determining the reactive center loop configuration in the native vaspin state and might contribute to the high thermostability of vaspin. Thus, this structure may provide a basis for future mutational studies
Observation of topological Hall effect in MnâRhSn films
Recently non-collinear magnetic structures have attracted renewed attention due to the novel Hall effects that they display. In earlier work evidence for a non-collinear magnetic structure has been reported for the ferromagnetic Heusler compound MnâRhSn. Using sputtering techniques we have prepared high quality epitaxial thin films of MnâRhSn by high temperature growth on MgO (001) substrates. The films are tetragonally distorted with an easy magnetization axis along the c-axis. Moreover, we find evidence for an anomalous Hall effect whose magnitude increases strongly below the Curie temperature that is near room temperature. Consistent with theoretical calculations of the anomalous Hall conductivity that we have carried out by deriving the Berry curvature from the electronic structure of perfectly ordered MnâRhSn, the sign of the anomalous Hall conductivity is negative, although the measured value is considerably smaller than the calculated value. We attribute this difference to small deviations in stoichiometry and chemical ordering. We also find evidence for a topological Hall resistivity of about 50 nΩ cm, which is âŒ5% of the anomalous Hall effect, for temperatures below 100 K. The topological Hall effect signifies the presence of a chiral magnetic structure that evolves from the non-collinear magnetic structure that MnâRhSn is known to exhibit
X-Ray Co-Crystal Structure Guides the Way to Subnanomolar Competitive Ecto-5 '-Nucleotidase (CD73) Inhibitors for Cancer Immunotherapy
Ecto-5'-nucleotidase (CD73, EC 3.1.3.5) catalyzes the extracellular hydrolysis of AMP yielding adenosine, which induces immunosuppression, angiogenesis, metastasis, and proliferation of cancer cells. CD73 inhibition is therefore proposed as a novel strategy for cancer (immuno)therapy, and CD73 antibodies are currently undergoing clinical trials. Despite considerable efforts, the development of small molecule CD73 inhibitors has met with limited success. To develop a suitable drug candidate, a high resolution (2.05 degrees A) co-crystal structure of the CD73 inhibitor PSB-12379, a nucleotide analogue, in complex with human CD73 is determined. This allows the rational design and development of a novel inhibitor (PSB-12489) with subnanomolar inhibitory potency toward human and rat CD73, high selectivity, as well as high metabolic stability. A co-crystal structure of PSB-12489 with CD73 (1.85 degrees A) reveals the interactions responsible for increased potency. PSB-12489 is the most potent CD73 inhibitor to date representing a powerful tool compound and novel lead structure
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