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- Wildes, A. R., et al.
(författare)
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High-resolution x-ray scattering from epitaxial thin films of Y/Nb on Al2O3
- 2020
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Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 32:37
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Tidskriftsartikel (refereegranskat)abstract
- During the 1990s, Roger Cowley had a strong interest in the crystal and magnetic structures of rare-earth superlattices as a means to understand the rich and exotic magnetic properties of the rare-earth metals. High-quality samples can be grown by molecular beam epitaxy on sapphire substrates by first depositing a thin epitaxial layer of niobium, then a layer of yttrium or lutetium as a seed. High-resolution x-ray scattering is an excellent probe to characterise the crystal quality and was used to study the structure of the niobium layer. However, relatively little attention was paid to the seed layer. This article summarises some of the x-ray experiments performed by the Cowley group to study the structure of epitaxial (110) niobium on (11 (2) over bar0) sapphire, and extends the work to report some results on the structure of thin (0 00 1) yttrium seed layers. The structure of the yttrium films is shown to have a strong dependence on the thickness of the niobium buffer, with the buffer needing to be thicker than a critical value of similar to 80 degrees A for the formation of misfit dislocations at the Nb/Al2O3 interface before highly coherent Y films can be grown. Yttrium films grown on Nb buffers thinner than similar to 500 degrees A show a similar two-peak line shape in q(perpendicular to) scans through their specular Bragg peaks to that seen in the specular Nb Bragg peaks, with a resolution-limited feature on a broader diffuse peak. The resolution-limited feature depends on the thickness of the yttrium film, becoming weaker and having a stronger decay with increasing q(parallel to) as the film thickness increases, while the width of the yttrium broad peak evolves as the square root of the width of the niobium Bragg peak. The data are discussed within the context of theories describing the scattering from films with misfit dislocations.
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- Maxwell, Karen L., et al.
(författare)
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Protein folding : Defining a "standard" set of experimental conditions and a preliminary kinetic data set of two-state proteins
- 2005
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Ingår i: Protein Science. - : Wiley. - 0961-8368 .- 1469-896X. ; 14, s. 602-16
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Tidskriftsartikel (refereegranskat)abstract
- Recent years have seen the publication of both empirical and theoretical relationships predicting the rates with which proteins fold. Our ability to test and refine these relationships has been limited, however, by a variety of difficulties associated with the comparison of folding and unfolding rates, thermodynamics, and structure across diverse sets of proteins. These difficulties include the wide, potentially confounding range of experimental conditions and methods employed to date and the difficulty of obtaining correct and complete sequence and structural details for the characterized constructs. The lack of a single approach to data analysis and error estimation, or even of a common set of units and reporting standards, further hinders comparative studies of folding. In an effort to overcome these problems, we define here a "consensus" set of experimental conditions (25°C at pH 7.0, 50 mM buffer), data analysis methods, and data reporting standards that we hope will provide a benchmark for experimental studies. We take the first step in this initiative by describing the folding kinetics of 30 apparently two-state proteins or protein domains under the consensus conditions. The goal of our efforts is to set uniform standards for the experimental community and to initiate an accumulating, self-consistent data set that will aid ongoing efforts to understand the folding process.
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- Miao, X. F., et al.
(författare)
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Short-range magnetic correlations and spin dynamics in the paramagnetic regime of (Mn,Fe)2(P,Si)
- 2016
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Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 94:1
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Tidskriftsartikel (refereegranskat)abstract
- The spatial and temporal correlations of magnetic moments in the paramagnetic regime of (Mn,Fe)(2)(P,Si) have been investigated by means of polarized neutron diffraction and muon-spin relaxation techniques. Short-range magnetic correlations are present at temperatures far above the ferromagnetic transition temperature (T-C). This leads to deviations of paramagnetic susceptibility from Curie-Weiss behavior. These short-range magnetic correlations extend in space, slow down with decreasing temperature, and finally develop into long-range magnetic order at T-C.
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- Ehlers, G., et al.
(författare)
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Generalization of the classical xyz-polarization analysis technique to out-of-plane and inelastic scattering
- 2013
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 84:9
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Tidskriftsartikel (refereegranskat)abstract
- The technique of longitudinal ("xyz") polarization analysis has been used successfully for many years to study disordered magnetic materials in thermal and cold neutron diffraction experiments. The technique allows the simultaneous and unambiguous separation of the nuclear, magnetic, and nuclear spin-incoherent contributions to the scattering. The technical advances seen in recent years, such as the availability of polarized He-3 analyzer cells to cover a large detector solid angle, the ability to detect out-of-plane scattering in a multi-detector, and a significant increase of the usable beam divergence, call for a generalization of the method. A general treatment of the formalism for carrying out neutron polarization analysis will be given in this paper, which describes a possible method of usage at a future, modern diffractometer or inelastic spectrometer with large area multi-detector coverage. (C) 2013 AIP Publishing LLC.
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- Korelis, Panagiotis T., et al.
(författare)
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Highly amorphous Fe90Zr10 thin films, and the influence of crystallites on the magnetism
- 2010
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:1, s. 404-409
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Tidskriftsartikel (refereegranskat)abstract
- A method for depositing highly amorphous, iron-rich Fe100-xZrx thin films on to room temperature substrates is presented. The method involves co-depositing Fe and Zr on to an amorphous AlZr layer. Experimental proof that the structures are completely amorphous is given by transmission electron microscopy and polarized neutron reflectometry. The reflectometry measurements also give an indication of the impact that Fe crystallite impurities have on the magnetic structure and properties of amorphous FeZr. The results are consistent with previous investigations on bulk samples, which showed that crystalline impurities make the magnetic structure more non-collinear.
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- Wildes, A. R., et al.
(författare)
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Some observations on polarized neutron reflectivity in applied fields
- 2008
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:295216
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Tidskriftsartikel (refereegranskat)abstract
- Unpolarized neutron reflectivity measurements on FeCo/Pt and Fe/Co superlattices have revealed a number of interesting features when a relatively large field was applied normal to the samples' surface. Some of the features, which include oscillations and Yoneda scattering below the critical edge, can be understood by calculating the polarization-dependent reflectivities and transmissions of the samples. Measurements with polarization analysis, however, show that the Zeeman-split reflected beams, expected in reflectivity experiments in an applied magnetic field, do not appear to have a unique spin state. The interpretation of the data is believed to lie in a non-collinearity between the axis for the reflected neutron beam polarization and the axis for the polarization analysis.
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