We study magnetic hysteresis loops after field cooling of a CoO/Co bilayer by MOKE and polarized neutron reflectivity. The neutron scattering reveals that the first magnetization reversal after field ...cooling is dominated by domain wall movement, whereas all subsequent reversals proceed essentially by rotation of the magnetization. In addition, off-specular diffuse scattering indicates that the first magnetization reversal induces an irreversible change of the domain state in the antiferromagnet.
The structure of polyelectrolyte multilayers built up by alternate adsorption of polyanions and polycations is investigated by X-ray reflectivity at the solid/air and neutron reflectivity at the ...solid/liquid interface. The experiments provide detailed information about the density gradient of polyelectrolyte chains across the film and show the influence of the water content of the film on the internal structure. The polyelectrolyte density is determined by the adsorption conditions (e.g. amount of NaCl) and cannot be changed by addition of salt after adsorption. After drying the film thickness is reduced by 30%.
A study of exchange bias phenomenon in ferrimagnetic /ferromagnetic FeGd/ FeSn bilayers is presented. The amorphous FeSn and FeGd alloys have been grown by co-evaporation. Specific growth conditions ...allow to induce an uniaxial anisotropy in both alloys in a parallel direction. After saturation of the bilayers under a positive field, the hysteresis loop of one of the layer is shifted towards a positive field HE. The sign of the exchange bias field HE is shown to be due to the antiferromagnetic coupling between the net magnetizations of both alloys. The field HE is studied as a function of the thickness of each layer and of the temperature. Using ac-susceptibility measurements and polarized neutron reflectometry, it is shown that the reversal of magnetization of the bilayers is dominated by the presence of a domain wall at the interface. This exchange bias system is shown to act as a potential well for the magnetic domain wall. Within this assumption and thanks to a precise magnetic characterization of each alloy, the evolution of HE with the thickness of the layers is well reproduced using simple one-dimensional analytical models for the domain wall or a more elaborate numerical approach. PACS. 75.60.Ch Domain walls and domain structure-75.70.-i Magnetic properties of thin films, surfaces, and interfaces-75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.)
ADAM, the new reflectometer at the ILL Schreyer, A; Siebrecht, R; Englisch, U ...
Physica. B, Condensed matter,
06/1998, Letnik:
248, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
The new reflectometer ADAM at the ILL is described and some of the results obtained in the first year of operation are presented. These include a reflectivity of a Si wafer over eight orders of ...magnitude, a measurement of a thick
56Fe/
57Fe isotope superlattice, and a polarised reflectivity of a Co/Cu multilayer. The instrument is now available to outside users.
Resonant magnetic X-ray scattering studies have been carried out recently to explore the phase transition and Néel temperature for the helical spin structure in single Ho films as a function of film ...thickness. However these experiments have a natural limit of about 200
Å, since with decreasing film thickness leaking charge scattering and finite thickness oscillations bury the magnetic satellite peaks. This limit hinders the investigation of scaling effects. Using neutron scattering we could now show that the intensity of the (00.2−
τ) and (00.0+
τ) magnetic satellite reflections are surprisingly large, allowing to explore the phase transition in epitaxial Ho(00.1) films down to below 50
Å.
By characterization of Fe/Si multilayers with a range of layer thickness we show that the diffusion of Si into Fe makes the Si layers 11.4±1.2
Å thinner than expected. We can use this information to ...improve growth of multilayers with high precision of layer thickness. Furthermore, the interdiffusion of Si into Fe creates a magnetically dead layer at the interface of about 5
Å. We have used reactive sputtering of Si with N
2 as a method to reduce interdiffusion. With the ability to control thickness more accurately and to reduce interdiffusion we have deposited polarizing Fe/SiN
x
supermirrors with neutron spin-up reflectivity in excess of 85% at
λ/
θ=0.3°/
λ (i.e., “
m=3”), allowing us to obtain neutron polarization above 95% in reflection geometry and above 90% in transmission geometry, respectively.
The distorted wave Born approximation (DWBA) is applied to evaluate the diffraction pattern of neutrons (or X-rays) from a 2D array of dots deposited onto a dissimilar substrate. With the radiation ...impinging on the surface at a grazing incidence angle
α, the intensities diffracted both in and out the plane of specular reflection are calculated as a function of the periodicity of the array, height and diameter of the dots. The results are presented in the form of diffracted intensity contours in a plane with coordinates
α and
α′, the latter being the glancing angle of scattering. The optimization of the experimental conditions for polarized neutron experiments on submicron dots is discussed. The feasibility of such measurements is confirmed by a test experiment.
We present a polarized neutron reflectometry study of the spin-reorientation in thin epitaxial grown Au (1
1
1)/Co/W-films. The transition as a function of Co-thickness
d
Co was investigated at
T=300
...K in the thickness range 10.4
Å⩽
d
Co⩽16.0
Å. For the Co film with
d
Co=16.0
Å we also measured the spin-reorientation-transition as a function of temperature within the range 10
K⩽
T⩽300
K.
The main characteristics of the new reflectometer ADAM at the ILL are described. A measured reflectivity of a Si wafer is shown, which demonstrates a dynamic range of up to 8 orders of magnitude. The ...instrument is now available to outside users.
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