| 1. |
- Oji, U.K., et al.
(författare)
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Implementation of time of flight polarized neutron imaging at IMAT-ISIS
- 2023
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 235
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we report the first case of design and implementation of a polarized neutron imaging option on the Imaging and Materials Science & Engineering Station (IMAT). This is a significant addition to the capabilities of the station that allows the characterization of advanced magnetic materials for different engineering applications. Combining its time-of-flight feature with a polarized beam yields data that facilitate both quantitative and qualitative analysis of magnetic materials. Using the simple field of an aluminium solenoid, we perform a characterization of the new setup. In addition, we present polarized measurements of additively manufactured (AM) MnAl samples where the magnetic anisotropy due to the fabrication process has been investigated as a first scientific application of the setup. The results indicate that the anisotropy of the material can be engineered through variation of the AM fabrication parameters.
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| 2. |
- Campillo, E., et al.
(författare)
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Observations of the effect of strong Pauli paramagnetism on the vortex lattice in superconducting CeCu2Si2
- 2021
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Ingår i: Physical Review B. - 2469-9950. ; 104:18
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of a study of the vortex lattice in the heavy fermion superconductor CeCu2Si2, using small-angle neutron scattering (SANS). In this material at temperatures well below Tc∼0.6 K, the value of the upper critical field Bc2∼2.2 T is strongly limited by the Pauli paramagnetism of the heavy fermions. In this temperature region, our SANS data show an increase in the magnetization of the flux line cores with field, followed by a rapid fall near Bc2. This behavior is the effect of Pauli paramagnetism and we present a theory-based model, which can be used to describe this effect in a range of materials. The pairing in CeCu2Si2 appears to arise from the effect of magnetic fluctuations, but the evidence for a d-wave order parameter is rather weak. We find that the vortex lattice structure in CeCu2Si2 is close to regular hexagonal. There are no phase transitions to square or rhombic structures; such transitions are expected for d-wave superconductors and observed in CeCoIn5; however, the temperature dependence of the SANS intensity indicates that both large and small gap values are present, most likely due to multiband s-wave superconductivity, rather than a nodal gap structure.
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| 3. |
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| 4. |
- Cameron, A. S., et al.
(författare)
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Probing superconducting order in overdoped Cax Y1-xBa2Cu3 O7 by neutron diffraction measurements of the vortex lattice
- 2023
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Ingår i: Physical Review B. - 2469-9950. ; 108:14
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Tidskriftsartikel (refereegranskat)abstract
- We present small-Angle neutron scattering studies of the magnetic vortex lattice (VL) in Ca0.04Y0.96Ba2Cu3O7 up to a field of 16.7 T and Ca0.15Y0.85Ba2Cu3O7 up to 25 T to investigate the general behavior of the superconducting gap in YBCO-based compounds at high magnetic field. We find in these overdoped compounds that the series of VL structure transitions have shifted down in field relative to those reported for the undoped compound. The hole doping by calcium is expected to alter the Fermi velocity and it reduces the upper critical field of the system. However, we attribute the VL changes mainly to the weakening of the 1D superconductivity in the Cu-O chains by the disorder introduced by doping. The high-field structure of the VL is similar to recent measurements on the parent compound in even higher fields of 25 T, which indicates that the fundamental d-wave nature of the superconducting gap is unchanged by calcium doping. This is corroborated by the temperature dependence of the VL form factor, which also shows the same d-wave behavior as observed in other cuprates. We also argue that they might be the explanation of Pauli paramagnetic effects in the field dependence of the VL form factor.
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| 5. |
- Jellyman, E., et al.
(författare)
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Unconventional superconductivity in the nickel chalcogenide superconductor TlNi2Se2
- 2020
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Ingår i: Physical Review B. - 2469-9950. ; 101:13
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of a study of the vortex lattice (VL) of the nickel chalcogenide superconductor TlNi2Se2, using small angle neutron scattering. This superconductor has the same crystal symmetry as the iron arsenide materials. Previous work points to it being a two-gap superconductor, with an unknown pairing mechanism. No structural transitions in the vortex lattice are seen in the phase diagram, arguing against d-wave gap symmetry. Empirical fits of the temperature dependence of the form factor and penetration depth rule out a simple s-wave model, supporting the presence of nodes in the gap function. The variation of the VL opening angle with field is consistent with earlier reports of multiple gaps
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| 6. |
- Shen, L., et al.
(författare)
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Concomitant interfacial spin fractal transformation and exchange bias in a magnetic shape memory alloy
- 2023
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Ingår i: Applied Physics Letters. - 0003-6951. ; 123:13
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Tidskriftsartikel (refereegranskat)abstract
- Small-angle neutron scattering is used to study the exchange bias effect in Mn50Ni40Sn10. The martensitic transformation is found to be responsible for the nanometer-scale spin clusters (SCs) inside the low-temperature ferromagnetic (FM) martensite phase. The magnetic field dependences of the SCs and FM domains exhibit an asymmetry that characterizes the exchange bias. We find that the surface geometries of the two magnetic phases are strongly susceptible to magnetization changes. While the FM domains and SCs are dominated by diffuse and fractal surfaces around the coercive fields, this configuration is reversed in the saturation regime, where the FM and SC surfaces become fractal and diffuse, respectively. These geometry changes are driven by the spin reorientation inside the heterogeneous FM/SC domain walls, where exchange anisotropy arises. Our work reveals the microscopic mechanism underlying the exchange bias effect in magnetic shape memory alloys.
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