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| 4. |
- Miao, X. F., et al.
(author)
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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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In: PHYSICAL REVIEW B. - 2469-9950. ; 94:1
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Journal article (peer-reviewed)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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| 5. |
- Edberg, Richard, et al.
(author)
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Dipolar spin ice under uniaxial pressure
- 2019
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 100:14
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Journal article (peer-reviewed)abstract
- The magnetically frustrated spin ice family of materials is host to numerous exotic phenomena such as magnetic monopole excitations and macroscopic residual entropy extending to low temperature. A finite-temperature ordering transition in the absence of applied fields has not been experimentally observed in the classical spin ice materials Dy2Ti2O7 and Ho2Ti2O7. Such a transition could be induced by the application of pressure, and in this work we consider the effects of uniaxial pressure on classical spin ice systems. Theoretically, we find that the pressure-induced ordering transition in Dy2Ti2O7 is strongly affected by the dipolar interaction. We also report measurements of the neutron structure factor of Ho2Ti2O7 under pressure and compare the experimental results to the predictions of our theoretical model.
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| 6. |
- Edberg, Richard, et al.
(author)
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Effects of uniaxial pressure on the spin ice Ho2Ti2O7
- 2020
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 102:18
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Journal article (peer-reviewed)abstract
- The spin ice materials Ho2Ti2O7 and Dy2Ti2O7 are experimental and theoretical exemplars of highly frustrated magnetic materials. However, the effects of applied uniaxial pressure are not well studied, and here we report magnetization measurements of Ho2Ti2O7 under uniaxial pressure applied in the [001], [111], and [110] crystalline directions. The basic features are captured by an extension of the dipolar spin ice model. We find a good match between our model and measurements with pressures applied along two of the three directions, and we extend the framework to discuss the influence of crystal misalignment for the third direction. The parameters determined from the magnetization measurements reproduce neutron scattering measurements that we perform under uniaxial pressure applied along the [110] crystalline direction. In the detailed analysis, we include the recently verified susceptibility dependence of the demagnetizing factor. Our work demonstrates the application of a moderate applied pressure to modify the magnetic interaction parameters. The knowledge can be used to predict critical pressures needed to induce new phases and transitions in frustrated materials, and in the case of Ho2Ti2O7 we expect a transition to a ferromagnetic ground state for uniaxial pressures above 3.3 GPa.
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| 7. |
- Sandberg, L. o., et al.
(author)
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Design, calibration, and performance of a uniaxial pressure cell for neutron scattering studies of quantum magnetism
- 2023
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 94:10
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Journal article (peer-reviewed)abstract
- We provide an overview of a pressure cell designed to apply uniaxial pressure to single crystals for the study, by neutron scattering techniques, of strongly correlated magnetic systems and, in particular, quantum magnets. A detailed overview of the pressure cell components, their requirements, and links to the scientific and technical specifications are presented. The pressure cell is able to accommodate a 200 mm(3) single crystal that can be pressurized up to 2 GPa at cryogenic temperatures. The pressure cell is consistent with the requirements of inelastic neutron scattering and, importantly, neutron polarization analysis. A particular strength of the uniaxial pressure cell is the highly uniform and low background for a wide scattering angle of 360(degrees) horizontally and +/- 20(degrees) vertically. We show the performance of the uniaxial pressure cell using a relevant neutron scattering instrument, the polarized diffuse scattering instrument, D7. The experiments confirm that the cell complies with the scientific and technical requirements. This uniaxial pressure cell will provide a useful additional tool in the sample environment suite available for the study of quantum magnetism.
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| 8. |
- Wildes, A. R., et al.
(author)
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High-resolution x-ray scattering from epitaxial thin films of Y/Nb on Al2O3
- 2020
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In: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 32:37
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Journal article (peer-reviewed)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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| 9. |
- Björck, Matts, et al.
(author)
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Segregation and interdiffusion in (Fe,Co)/Pt superlattices
- 2009
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:8, s. 085428-
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Journal article (peer-reviewed)abstract
- We report on the chemical structure of (Fe,Co)/Pt superlattices, which recently have shown high uniaxial magnetocrystalline anisotropy combined with high saturation magnetic moments. In particular, the homogeneity of the (Fe,Co) alloy is studied with a combination of x-ray and neutron reflectometry-the latter in a configuration where magnetic scattering is negligible. It is deduced, with support from off-specular x-ray reflectivity patterns and corresponding simulations, that the lower (Fe,Co)-on-Pt interface contains more Co than the upper Pt-on-(Fe,Co) interface. This can occur as Co interdiffuses into Pt more easily than Fe, as shown by density-functional calculations. The effect of this interdiffusion and segregation on the uniaxial anisotropy is discussed, and it is found that the previously observed discrepancy between experimental and theoretical anisotropy values can be quantitatively accounted for.
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| 10. |
- Ehlers, G., et al.
(author)
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Generalization of the classical xyz-polarization analysis technique to out-of-plane and inelastic scattering
- 2013
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 84:9
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Journal article (peer-reviewed)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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| 11. |
- Jacobsen, Henrik, et al.
(author)
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Spin dynamics of the director state in frustrated hyperkagome systems
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9969 .- 2469-9950. ; 104:5
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Journal article (peer-reviewed)abstract
- We present an experimental study of the magnetic structure and dynamics of two frustrated hyperkagome compounds, Gd3Ga5O12 and Gd3Al5O12. It has previously been shown that Gd3Ga5O12 exhibits long-range correlations of multipolar directors that are formed from antiferromagnetic spins on loops of ten ions. Using neutron diffraction and reverse Monte Carlo simulations we prove the existence of similar magnetic correlations in Gd3Al5O12, showing the ubiquity of these complex structures in frustrated hyperkagome materials. Using inelastic neutron scattering we shed further light on the director state and the associated low-lying magnetic excitations. In addition, we have measured quasielastic dynamics that show evidence of spin diffusion. Finally, we present AC susceptibility measurements on both Gd3Ga5O12 and Gd3Al5O12, revealing a large difference in the low-frequency dynamics between the two otherwise similar compounds.
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| 12. |
- Korelis, Panagiotis T., et al.
(author)
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Highly amorphous Fe90Zr10 thin films, and the influence of crystallites on the magnetism
- 2010
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:1, s. 404-409
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Journal article (peer-reviewed)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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| 15. |
- Maxwell, Karen L., et al.
(author)
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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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In: Protein Science. - : Wiley. - 0961-8368 .- 1469-896X. ; 14, s. 602-16
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Journal article (peer-reviewed)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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| 16. |
- Wildes, A. R., et al.
(author)
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Some observations on polarized neutron reflectivity in applied fields
- 2008
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:295216
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Journal article (peer-reviewed)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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