| 1. |
|
|
| 2. |
- Arnalds, Unnar B., 1976-
(författare)
-
Magnetic Order in Artificial Structures
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The topic of this thesis is the investigation of the magnetic properties of artificially created magnetic structures. Applying different characterization techniques, ranging from direct imaging methods to reciprocal space techniques, the properties of lithographically patterned arrays of magnetic thin film and multilayer elements are investigated by exploring their magnetic state, extending from the atomic scale up to collective ordering phenomena of nano-magnetic elements.Laterally patterned amorphous multilayer arrays of combined circular and ellipsoidal islands were investigated. The arrays contain a variety of length scales, ranging from their nanometer scale multilayer structure to their lateral periodicity in the micrometer range. The attributes of these arrays are explored using different techniques, applicable for addressing the magnetization at different length scales, including magneto-optical techniques, micromagnetic simulations and x-ray resonant magnetic scattering.Arrays of dipole interacting elongated magnetic elements composed of Pd(Fe) thin films were investigated. Pd(Fe) films have a low Curie temperature which can be tuned by the thickness of the Fe layer embedded in Pd. By this, the interaction and the shape anisotropy energies can be brought down to energy scales comparable to room temperature enabling the possibility of investigating the effect of thermal excitations on such arrays. The temperature dependent magnetization of an artificial square spin ice array was investigated by magneto-optical measurements demonstrating the possibility of observing an order-disorder transition in an artificial square spin ice system. The role of dipolar interactions and the possibility of achieving thermal ground state ordering was then further investigated by magnetically sensitive photoemission electron microscopy imaging of ring arrangements of elongated Pd(Fe) elements. The results reveal a high probability of achieving a thermal ground state ordering of the magnetization of the islands.
|
|
| 3. |
- Dennison, Andrew J. C., et al.
(författare)
-
Graphite intercalation compound (GIC) crystal monochromators for cold neutron instruments : Characterization of KC24 by time-of-flight neutron diffraction
- 2021
-
Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 92:2
-
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.
|
|
| 4. |
- Durr, Hermann A., et al.
(författare)
-
A Closer Look Into Magnetism : Opportunities With Synchrotron Radiation
- 2009
-
Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 45:1, s. 15-57
-
Forskningsöversikt (refereegranskat)abstract
- The unique properties of synchrotron radiation, such as broad energy spectrum, variable light polarization, and flexible time structure, have made it an enormously powerful tool in the study of magnetic phenomena and materials. The refinement of experimental techniques has led to many new research opportunities, keeping up with the challenges put up by modern magnetism research. In this contribution, we review some of the recent developments in the application of synchrotron radiation and particularly soft X-rays to current problems in magnetism, and we discuss future perspectives.
|
|
| 5. |
- Gutfreund, Philipp, et al.
(författare)
-
Depletion at solid/liquid interfaces : Flowing hexadecane on functionalized surfaces
- 2011
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:6, s. 064711-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a neutron reflectivity study on interfaces in contact with flowing hexadecane, which is known to exhibit surface slip on functionalized solid surfaces. The single crystalline silicon substrates were either chemically cleaned Si(100) or Si(100) coated by octadecyl-trichlorosilane (OTS), which resulted in different interfacial energies. The liquid was sheared in situ and changes in reflectivity profiles were compared to the static case. For the OTS surface, the temperature dependence was also recorded. For both types of interfaces, density depletion of the liquid at the interface was observed. In the case of the bare Si substrate, shear load altered the structure of the depletion layer, whereas for the OTS covered surface no effect of shear was observed. Possible links between the depletion layer and surface slip are discussed. The results show that, in contrast to water, for hexadecane the enhancement of the depletion layer with temperature and interfacial energy reduces the amount of slip. Thus a density depletion cannot be the origin of surface slip in this system.
|
|
| 6. |
- Hjörvarsson, Björgvin, et al.
(författare)
-
The influence of weak links on magnetic ordering in layered structures
- 2008
-
Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 61:1, s. 17008-
-
Tidskriftsartikel (refereegranskat)abstract
- We discuss the magnetic ordering in layered magnets with two different inherent ordering temperatures. A [V(12 ML)Fe(2 ML)/V(12 ML)(/Fe(3 ML)](70) superlattice with anti-ferromagnetic interlayer exchange coupling is used for this purpose. The more rapid decrease of the magnetic moment in the 2 monolayer thick Fe layers influences the ordering in a non-trivial way. A distribution of the effective ordering temperature is inferred, originating from a more rapid decrease of the magnetic moment in the near-surface region, as compared to the interior of the sample. The results clearly demonstrate the need to consider all energy and length scales when addressing ordering in materials with finite extension.
|
|
| 7. |
- Kravtsov, Evgeny, et al.
(författare)
-
Onset of spin-density-wave antiferromagnetism in Cr/V multilayers
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:2, s. 024421-
-
Tidskriftsartikel (refereegranskat)abstract
- Spin-density-wave (SDW) magnetism in a series of Cr/V heterostructures with different Cr thicknesses was systematically investigated by combined resistivity, neutron, and synchrotron scattering measurements. We show that the onset of the bulklike SDW state comes through several necessary steps from a paramagnetic state through a commensurate SDW to an incommensurate SDW. The Néel temperature for the incommensurate SDW is found to scale with Cr thickness and reaches the bulk value at a Cr thickness of about 2000 Å. The proximity effect from Cr/V interfaces is found to lead to (i) the appearance of a 50-Å magnetically dead Cr layer near Cr/V interfaces and (ii) suppression of the spin-flip transition and stabilization of a single-domain SDW with out-of-plane spins and out-of-plane propagation wave vector. Finally, we show that the SDW period increases with decreasing Cr thickness and becomes temperature independent in sufficiently thin Cr layers.
|
|
| 8. |
|
|
| 9. |
- Remhof, Arndt, et al.
(författare)
-
Hydrogen assisted growth of Fe/V superlattices
- 2006
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 18:35, s. L441-L445
-
Tidskriftsartikel (refereegranskat)abstract
- The functionality of magnetic heterostructures is strongly affected by the interface structure and morphology as well as by the crystalline quality. Using Fe/V superlattices, serving as model systems for exchange coupling and for superconducting spin valves, we show that the excellent interfacial properties can be further improved by hydrogen assisted growth. The role of the hydrogen thereby is twofold. It reduces thickness fluctuations and improves the crystalline quality. Sputter deposited Fe/V superlattices grown at a partial pressure of 2 x 10(-6) mbar are atomically flat and possess a residual resistivity ratio which is significantly improved as compared to those of conventionally grown samples.
|
|
| 10. |
- Walz, Marco, et al.
(författare)
-
Micellar Crystallization with a Hysteresis in Temperature
- 2010
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 26:18, s. 14391-14394
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the phase diagram of the triblock copolymer P123 solved in water by viscosity measurements for different concentrations and temperatures The structures of the different phases were identified by surface sensitive neutron diffraction We find a pronounced hysteresis between heating and cooling During heating, a highly viscous crystalline fee phase is found before melting occurs at 44 degrees C with a simultaneous drop in viscosity Upon cooling, first a hexagonal phase with low viscosity develops followed by a highly viscous fee phase Phase diagrams for the heating and cooling cycle for different concentrations are provided The hysteric behavior is discussed in relation to the shape of the micelles
|
|
