A. V. Petrenko

Ordering in magnetic multilayers by off-specular neutron scattering

The combination of specular reflection and off-specular scattering with polarized neutrons gives a unique detailed information on the lateral and transverse spin-configuration of a magnetic multilayer stack. We present the first direct experimental observation of a phenomenon predicted theoretically for antiferromagnetically coupled multilayers: the twisted ground-state configuration in an external magnetic field. This twisted configuration arises due to the reduced symmetry of magnetic moments of the end layers having only one neighbor. This fact can be established directly via the qualitative analysis of the line shape of the superstructure peaks on the specular line and the related off-specular Bragg sheet. Additional quantitative evaluation of both specular reflection and off-specular scattering allows one to deduce the layer-by-layer spin configuration through the multilayer stack, as well as within the plane of the layer. The presence of spin-flip off-specular scattering means that the layer magnetization is laterally not homogeneous but is decomposed into a set of domains. The distribution of magnetic moments within each domain, the domains size and their distributions are obtained.

Refraction of polarized neutrons in a magnetically non-collinear layer

Abstract The refraction of polarized neutrons in a magnetic layer in relation to the neutron wavelength, the magnitude and direction of an external magnetic field, has been investigated experimentally. The effects of space splitting of the polarized neutron beam and the interference of neutron beams with different spin states have been observed and measured.

Domains and interface roughness in Fe/Cr multilayers: Influence on the GMR effect

Abstract Different types of roughness in magnetic multilayers can be distinguished with off-specular neutron scattering. We report on roughness originating from magnetic domains in Fe/Cr multilayers and on structural roughness being created at the Fe–Cr interfaces. The influence of these types of roughness on the GMR-effect is outlined.

System of neutron microbeams from a planar waveguide

Results of experimental investigations of space, angular and wavelength distribution in neutron microbeams obtained for the first time with the help of a resonant planar neutron waveguide at the time-of-flight reflectometer of the IBR-2 pulsed reactor are reported and comparison with theoretical calculations is presented. Possible application of microbeams in physical experiments is discussed.

Nonreciprocal cell for neutrons

The effect of nonreciprocal transmission of thermal neutrons (λ = 3–6 Å) through a system of magnetic mirrors with a noncoplanar distribution of the magnetic induction is predicted and observed experimentally. The relative difference between the transmittances for the direct and inverse processes reaches 75%. Thereby, the feasibility of a nonreciprocal cell for spin-1/2 particles is demonstrated.

Neutron resonances in planar waveguides

We report on the results of the experimental investigation of the spectral width of neutron resonances in planar waveguides using the time-of-flight method and recording the microbeam emerging from the waveguide end. Experimental data are compared with the results of theoretical calculations.

Features of the magnetic state of the layered Fe-V nanostructure of the superconductor-ferromagnet type

The magnetic state of the V(39 nm)/20 [V(3 nm)/Fe(3 nm)] nanostructure has been investigated by polarized neutron reflectometry in the temperature range from 1.6 to 30 K in magnetic fields from 0.2 to 15 kOe. The data obtained indicate that the superconductivity of vanadium layers may affect magnetic ordering both over the depth of the structure and in its plane.

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.

Isotope-Identifying neutron reflectometry

The possibilities of an isotope-indentifying study of layered structures in different regimes of a neutron wave field are considered. The detection of specularly reflected neutrons and secondary radiation (caused by neutron capture) in the form of charged particles, γ quanta, and nuclear fission fragments, as well as neutrons spin-flipped in a noncollinear magnetic field and on nuclei of elements with spin, makes it possible to implement isotope-indentifying neutron reflectometry.

Polarized neutrons at pulsed sources in Dubna

The evolution of investigations with polarized neutrons using pulsed neutron sources with short and long pulses in Dubna is discussed. Some peculiarities of the use of long-pulse neutron sources are investigated.