V. Lauter-Pasyuk

Effect of nanoparticle size on the internal structure of copolymer-nanoparticles composite thin films studied by neutron reflection

Abstract Neutron reflection was used for the study of the composite films made of symmetric (d-PS-PBMA) diblock copolymer (molecular weight Mw = 170 and 135 K) with nanoparticles of γ-Fe2O3 (4 and 6 nm in diameter) incorporated in the deuterated PS-domains with different concentrations. From the neutron reflection experiment we determined the period of the lamellar structure and the position of the nanoparticles in the PS-layers. It is important to examine the effect of the particle size on the lamellar structure. We determined that the small nanoparticles (4 nm) concentrate close to d-PS-PBMA interfaces while larger nanoparticles (6 nm) localize in the center of PS domains. This effect is of considerable interest in the elaboration of new composite materials since it will give a control on the particle distribution inside the host domains.

Neutron reflectivity studies of composite nanoparticle - copolymer thin films

Neutron reflection was used for the investigation of a new class of copolymers – composite materials, consisting of symmetric polystyrene–polybuthylmethacrylate (PS–PBMA) diblock copolymer with incorporated nanoparticles γ-Fe2O3 of a few nanometers in diameter. The presence of the nanoparticles induces an elastic distortion of the copolymer matrix. From the experiments we obtained information about the lamellar order of the polymer matrix, the distribution of the nanoparticles in the film and the distortion of the interfaces caused by the nanoparticles.

Towards 3D polarization analysis in neutron reflectometry

General equations for spin-flip and non-spin-flip specular reflection and off-specular scattering are analyzed for the case of multidomain states of magnetic multilayers. The results are illustrated by numerical calculations performed for Fe/Cr multilayers using an original software developed on the basis of the supermatrix formalism. This routine allows to calculate the reflectivities and scattering cross sections from the layered structures of any complexity for any directions of the incident polarization vector and directions of the polarization analysis.

Magnetic flux distribution inside an YBa2Cu3O7 superconducting thin film in the mixed state

The stud). with polarized neutron reflection showed the spatially resolved nuclear and magnetic structure in a high-temperature superconducting (HT,) film of YBa2Cu,0, in the mixed state in an external field parallel to its surfam. The obtajned magnetic flux profile is composed of the penetrating Meissner field and the flux-line rows. The Aux-line rows show good linear arrangements. .4 local critical magnetization inside the HT, filnl was determined. The total magnetization exhibits flux-line row transirions and increases in average tvith increasing external field due to the surface barrier and the Aus-line interaction. 1999 Elsevicr Science B.V. All rights reserved.

Magnetic field distribution around flux-lines in YBa2Cu3O7 superconducting thin films in a parallel field

Abstract The magnetic field distribution inside thin YBa2Cu3O7 films in the mixed state was studied by polarized neutron reflection. The external field was parallel to the film surface, the thickness of the films was smaller or about equal to the London penetration depth λ. The obtained scattering length density distribution suggests that the magnetic field dependence around a flux-line is changed through the restricted geometry of the thin film. The decay of the magnetic field around a flux-line is not anymore governed by λ but by the thickness of the film.

Direct measurement of the magnetic field penetration depth in YBa2Cu3O7 superconducting films by polarized neutron reflectometry

Abstract A study of the magnetic field penetration depth in a high-temperature (HTc) superconducting film was performed with polarized neutron reflectometry in two scattering geometries. The fit to the reflectivity curves yielded the neutron-scattering length density profile and thus a precise image of the composition of the film. The film had a good quality seen by a not noticeable off-specular scattering. The fit to the spin asymmetry gave a magnetic-penetration depth of 1350 ± 150 A along the c-axis at a temperature T = 2 K. The model included an intrinsic exponential decay of the penetration depth. For the first time the spin asymmetry was determined with high resolution over an extended Q-range for a HTc-film.