| 1. |
- Dikaia, Olga, et al.
(författare)
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Magnetic contrast layers with functional SiO2 coatings for soft-matter studies with polarized neutron reflectometry
- 2024
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Ingår i: Journal of Applied Crystallography. - 0021-8898. ; 57:Pt 4, s. 1145-1153
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Tidskriftsartikel (refereegranskat)abstract
- This study introduces silicon substrates with a switchable magnetic contrast layer (MCL) for polarized neutron reflectometry (PNR) experiments at the solid–liquid interface to study soft-matter surface layers. During standard neutron reflectometry (NR) experiments on soft-matter samples, structural and compositional information is obtained by collecting experimental data with different isotopic contrasts on the same sample. This approach is normally referred to as contrast matching, and it can be achieved by using solvents with different isotopic contrast, e.g. different H2O/D2O ratios, and/or by selective deuteration of the molecules. However, some soft-matter systems might be perturbed by this approach, or it might be difficult to implement, particularly in the case of biological samples. In these scenarios, solid substrates with an MCL are an appealing alternative, as the magnetic contrast with the substrate can be used for partial recovery of information on the sample structure. More specifically, in this study, a magnetically soft Fe layer coated with SiO2 was produced by ion-beam sputter deposition on silicon substrates of different sizes. The structure was evaluated using X-ray reflectometry, atomic force microscopy, vibrating sample magnetometry and PNR. The collected data showed the high quality and repeatability of the MCL parameters, regardless of the substrate size or the thickness of the capping SiO2 layer. Previously proposed substrates with an iron MCL used an Au capping layer. The SiO2 capping layer proposed here allows reproduction of the typical surface of a standard silicon substrate used for NR experiments and is compatible with a large variety of soft-matter samples. This application is demonstrated with ready-to-use 50 x 50 x 10 mm substrates in PNR experiments for the characterization of a lipid bilayer in a single solvent contrast. Overall, the article highlights the potential of PNR with an MCL for the investigation of soft-matter samples.
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| 2. |
- Broekhuijsen, Sjoerd, 1993-, et al.
(författare)
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Synthesis and characterization of 11B4C containing Ni/Ti multilayers using combined neutron and X-ray reflectometry
- 2023
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Ingår i: Optical Materials Express. - : Optica Publishing Group. - 2159-3930. ; 13:4, s. 1140-1149
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Tidskriftsartikel (refereegranskat)abstract
- The performance of multilayers in optical components, such as those used in neutron scattering instruments, is crucially dependent on the achievable interface width. We have shown how the interface width of Ni/Ti multilayers can be improved using the incorporation of B4C to inhibit the formation of nanocrystals and limit interdiffusion and intermetallic reactions at the interfaces. A modulated ion-assistance scheme was used to prevent intermixing and roughness accumulation throughout the layer stack. In this work we investigate the incorporation of low-neutron-absorbing 11B4C for Ni/Ti neutron multilayers. Combined fitting of neutron reflectivity and X-ray reflectivity measurements shows an elimination of accumulated roughness for the 11B4C containing multilayers with a mean interface width of 4.5 Å, resulting in an increase in reflectivity at the first Bragg peak by a factor of 2.3 and 1.5 for neutron and X-ray measurements, respectively.
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| 3. |
- Chakravarty, Sujay, et al.
(författare)
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Simultaneous measurement of volume and grain boundary diffusivity separately in Fe thin film with stable nanostructure using polarized neutron reflectivity
- 2016
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Ingår i: Materials Research Express. - : IOP PUBLISHING LTD. - 2053-1591. ; 3:8
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Tidskriftsartikel (refereegranskat)abstract
- Polarized neutron reflectivity (PNR) measurements have been used for simultaneous measurement of volume and grain boundary diffusivity separately in stable nanocrystalline Fe thin film at very low homologous temperature (0.2 T-m < T < 0.3 Tm). PNR measurements were done on Si (substrate)/Fe (150 nm)/[Fe-57 (3 nm)/Fe-nat (9 nm)](x10) thin film system with periodic Fe-57 isotope modulation. PNR from as deposited film shows strong Bragg peaks due to neutron scattering length contrast between Fe-57 and Fe-nat layers. Atomic Diffusivity was measured from decrease in the intensity of the Bragg peak due to interdiffusion of Fe-57 and Fe-nat layers after annealing the film at three different temperatures 418 K, 483 K and 548 K, respectively for different time intervals starting from 30 min to several hours. The change in the nanostructure of the film after annealing is characterized using grazing incidence x-ray diffraction. No appreciable grain growth within error bar is observed in the film after annealing indicating that the diffusion measurements were done in stable nanostructure. It is observed that the grain boundary diffusivity is two orders of magnitude higher than the volume diffusivity. However, the mechanism of atomic diffusion is similar in both grain and grain boundary.
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| 4. |
- Chen, K., et al.
(författare)
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Observation of a Chirality-Induced Exchange-Bias Effect
- 2019
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- Chiral magnetism that manifests in the existence of skyrmions or chiral domain walls offers an alternative way for creating anisotropies in magnetic materials that might have large potential for application in future spintronic devices. Here we show experimental evidence for an alternative type of in-plane exchange-bias effect present at room temperature that is created from a chiral 90 degrees domain wall at the interface of a ferrimagnetic-ferromagnetic Dy-Co/Ni-Fe bilayer system. The chiral interfacial domain wall forms due to the exchange coupling of Ni-Fe and Dy-Co at the interface and the presence of Dzyaloshinskii-Moriya interaction in the Dy-Co layer. As a consequence of the preferred chirality of the interfacial domain wall, the sign of the exchange-bias effect can be reversed by changing the perpendicular orientation of the Dy-Co magnetization. The chirality-created tunable exchange bias in Dy-Co/Ni-Fe is very robust against high in-plane magnetic fields (mu H-0 <= 6 T) and does not show any aging effects. Therefore, it overcomes the limitations of conventional exchange-bias systems.
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| 5. |
- Dennison, Andrew J. C., et al.
(författare)
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Graphite intercalation compound (GIC) crystal monochromators for cold neutron instruments : Characterization of KC24 by time-of-flight neutron diffraction
- 2021
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 92:2
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Tidskriftsartikel (refereegranskat)abstract
- Graphite intercalation compounds (GICs) are a group of layered materials that are suitable as monochromators for cold neutrons. KC24 is a particularly interesting compound in this regard as it features a large c-axis lattice spacing of 8.74 angstrom, high reflectivity, and the possibility to produce large crystals with mosaicity that matches the beam divergence of cold neutron guides. GICs can be synthesized with different levels of intercalation, known as the stage of the compounds. Each stage displays a specific d-spacing. Impure GIC-monochromators containing multiple stages produce mixing of neutron wavelengths, which complicates data analysis on neutron reflectometers. We discuss the implications of GIC crystal purity and stage contamination for neutron reflectometry and show how GIC crystals can be characterized by time-of-flight neutron diffraction providing an efficient and quantifiable measure of the reflected wavelength spectrum. This allows taking into account multiple wavelength contaminations and ascertains the robustness of reflectometry measurements.
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| 6. |
- Dobrynin, A. N., et al.
(författare)
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On the origin of positive exchange bias and coercivity enhancement in proximity to the blocking temperature
- 2021
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 520
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic properties of two oxidised Co thin films prepared by different sputtering techniques are analysed. Exchange bias (EB) blocking temperatures (T-B) of the samples were found to be 50 K different due to difference in grain sizes of antiferromagnetic CoO. In proximity to T-B the EB changes its sign from negative to positive. This positive EB behaviour is strikingly similar for the two samples with the exception of its position on the temperature scale. A computational model, taking into account temperature dependence of the antiferromagnet's magnetocrystalline anisotropy and its sublattices' magnetisation, reproduces positive EB in proximity to T-B. This happens when a significant fraction of antiferromagnetic entities becomes involved in magnetisation reversal, and there is antiferromagnetic exchange coupling between those entities. The coercivity enhancement, accompanying positive EB, is due to anisotropy energies of the reversible antiferromagnetic entities contributing to the ferromagnetic layer's energy barrier. The model suggests that in order for the two samples to have identical positive EB behaviour, the reversible antiferromagnetic entities should represent individual spins.
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| 7. |
- Dorri, Samira, 1988-, et al.
(författare)
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Enhanced quality of single crystal CrBx/TiBy diboride superlattices by controlling boron stoichiometry during sputter deposition
- 2024
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584.
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Tidskriftsartikel (refereegranskat)abstract
- Single-crystal CrB2/TiB2 diboride superlattices with well-defined layers are promising candidates for neutron optics. However, excess B in sputter-deposited TiBy using a single TiB2 target deteriorates the structural quality of CrBx/TiBy (0001) superlattices. We study the influence of co-sputtering of TiB2 + Ti on the stoichiometry and crystalline quality of 300-nm-thick TiBy single layers and CrBx/TiBy (0001) superlattices on Al2O3(0001) substrates grown by DC magnetron sputter epitaxy at growth-temperatures TS ranging from 600 to 900 °C. By controlling the relative applied powers to the TiB2 and Ti magnetrons, y could be reduced from 3.3 to 0.9. TiB2.3 grown at 750 °C exhibited epitaxial domains about 10x larger than non-co-sputtered films. Close-to-stoichiometry CrB1.7/TiB2.3 superlattices with modulation periods Λ = 6 nm grown at 750 °C showed the highest single crystal quality and best layer definition. TiB2.3 layers display rough top interfaces indicating kinetically limited growth while CrB1.7 forms flat and abrupt top interfaces indicating epitaxial growth with high adatom mobility.
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| 8. |
- Forooqi Motlaq, Vahid, et al.
(författare)
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Dissolution mechanism of supported phospholipid bilayer in the presence of amphiphilic drug investigated by neutron reflectometry and quartz crystal microbalance with dissipation monitoring
- 2022
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier. - 0005-2736 .- 1879-2642. ; 1864:10
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Tidskriftsartikel (refereegranskat)abstract
- The influence and interaction of the ionizable amphiphilic drug amitriptyline hydrochloride (AMT) on a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) phospholipid bilayer supported on a silica surface have been investigated using a combination of neutron reflectometry and quartz crystal microbalance with dissipation monitoring. Adding AMT solutions with concentrations 3, 12, and 50 mM leaves the lipid bilayer mainly intact and we observe most of the AMT molecules attached to the head-group region of the outer bilayer leaflet. Virtually no AMT penetrates into the hydrophilic head-group region of the inner leaflet close to the silica surface. By adding 200 mM AMT solution, the lipid bilayer dissolved entirely, indicating a threshold concentration for the solubilization of the bilayer by AMT. The observed threshold concentration is consistent with the observation that various bilayer structures abruptly transform into mixed AMT-DOPC micelles beyond a certain AMT-DOPC composition. Based on our experimental observations, we suggest that the penetration of drug into the phospholipid bilayer, and subsequent solubilization of the membrane, follows a two-step mechanism with the outer leaflet being removed prior to the inner leaflet.
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| 9. |
- Grigoryeva, Natalia A., et al.
(författare)
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Mesostructure and Magnetic Properties of SiO2-Co Granular Film on Silicon Substrate
- 2022
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Ingår i: MAGNETOCHEMISTRY. - : MDPI. - 2312-7481. ; 8:12
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Tidskriftsartikel (refereegranskat)abstract
- Granular films SiO2(Co) exhibit unusual magnetic and magnetotransport properties which are strongly dependent on the composition of the film and material of a substrate. For example, the injection magnetoresistance (IMR) coefficient reaches a giant (GIMR) value of 10(5)% at room temperature in SiO2(Co) films on an n-GaAs substrate. However, the IMR effect is negligible in the case of a similar granular film deposited on the n-Si substrate. In this report, the structural and magnetic properties of granular film SiO2(Co) on Si substrate are studied with the aim to understand the cause of the difference in IMR coefficients for SiO2(Co) thin film deposited on n-GaAs and on n-Si substrates. Investigations were carried out using complementary methods of Polarized Neutron Reflectometry, Grazing Incidence Small-Angle X-ray Scattering, X-ray Reflectometry, Scanning Electron Microscope, and SQUID magnetometry. It is shown that the interface layer between the granular film and Si substrate exhibits metallic rather than magnetic properties and eliminates the GIMR effect. This interface layer is associated with the Si diffusion to Co nanoparticles and the formation of the metallic cobalt silicides.
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| 10. |
- Guasco, Laura, et al.
(författare)
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Emergent Magnetic Fan Structures in Manganite Homojunction Arrays
- 2022
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Ingår i: Advanced Materials. - : John Wiley & Sons. - 0935-9648 .- 1521-4095. ; 34:35
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Tidskriftsartikel (refereegranskat)abstract
- Devices with tunable magnetic noncollinearity are important components of superconducting electronics and spintronics, but they typically require epitaxial integration of several complex materials. The spin-polarized neutron reflectometry measurements on La1-xSrxMnO3 homojunction arrays with modulated Sr concentration reported herein have led to the discovery of magnetic fan structures with highly noncollinear alignment of Mn spins and an emergent periodicity twice as large as the array's unit cell. The neutron data show that these magnetic superstructures can be fully long-range ordered, despite the gradual modulation of the doping level created by charge transfer and chemical intermixing. The degree of noncollinearity can be effectively adjusted by low magnetic fields. Notwithstanding their chemical and structural simplicity, oxide homojunctions thus show considerable promise as a platform for tunable complex magnetism and as a powerful design element of spintronic devices.
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