Study of magnetic properties of Pd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>0.95</Subscript>Mn<Subscript>0.05</Subscript> alloy using polarized muons and neutrons

The Pd_1?x Fe _x )_0.95Mn_0.05 alloy with random competing interaction was studied by measuring the muon spin relaxation in an external transverse magnetic field and in a zero magnetic field. Using the measured temperature dependence of the dynamic relaxation rate λ and the characteristics of the distribution of local static fields, the phase states of the sample under study are refined. In particular, it is shown that the ferromagnetic and spin-glass states coexist simultaneously in the sample below 25 K. Combined studies of the sample using the μSR and neutron depolarization methods made it possible to determine the size of magnetic inhomogeneities to be 2–6 μm in the temperature range 5–40 K.     

Potential for Using Negative Spin Components in Neutron Polarizers. First Results

Technical Physics - The results of experimental verification of the feasibility of enhancing the efficiency of neutron-beam polarizers based on magnetized supermirrors are presented. The idea is to...     

Reflectometer for studying the surface of liquid systems

To study the free surface of liquids, a Reverans reflectometer with a vertical neutron scattering plane has been designed and is fabricated at Petersburg Nuclear Physics Institute. This reflectometer is intended to investigate surfaces and interfaces in liquid magnetic or nonmagnetic systems. The principles of reflectometer operation are described. The general view of the reflectometer with ready units is presented and its main technical parameters are given. The results of preliminary tests are reported.     

Present status and prospects for Spin-Echo Small-Angle Neutron Scattering (SESANS) at PIK neutron source

We discuss the present status and the prospects of Spin-Echo Small-Angle Neutron Scattering (SESANS) against the background of the available expertise and the neutron source PIK at PNPI (Gatchina). Two options for SESANS instruments are reviewed: (1) monochromatic with π-flipping permalloy foils and (2) with adiabatic radio frequency spin flippers in a white beam, combined with time-of-flight data collection. A software tool for quantitative prediction of the technical properties of option (2) is developed. For both options, we show that a SESANS instrument which can compete with instruments elsewhere, is realistic. For option (2), we suggest a perspective of spin-echo-length range such that neutron interference experiments become feasible.     

Effect of the rotation of an external magnetic field on the internal flux distribution in superconducting ceramics: Experiments with polarized neutrons

The behavior of a magnetic flux in a ceramic high-temperature superconductor with rotation of a magnetic field through a specified angle has been investigated using polarized neutrons. Two models of penetration of a weak magnetic field into a granular superconductor have been discussed. Based on the obtained distributions of the rotation angle and the magnitude of the magnetic field inside the sample, the choice is made in favor of one of these models.     

Neutron reflectometry with vector polarization analysis: First steps

The most detailed and reliable information about the magnetic state (magnetization depth profiles) of layers can be obtained by neutron reflectometry with vector polarization analysis. Two schemes of realization of this technique are considered. Precession coils designed to manipulate the polarization vector of monochromatic beams are used in scheme I. This scheme was tested at the neutron reflectometer NR-4M (PNPI, Gatchina). The earliest experimental data on the polarization vector rotation are reported, giving direct evidence of the wave function phase shift of a massive particle, the neutron, under total reflection. The basic elements for scheme II are remanent supermirrors. This scheme is designed for use with a white beam and is advantageous for pulse neutron sources. The effect of stray fields produced by remanent supermirrors on the neutron polarization has been theoretically and experimentally evaluated; efficient ways of compensating the stray fields are proposed.     

Spin-echo small-angle neutron scattering device: Test experiment using SiO2 colloidal particles

The results of the first experiments with a spin-echo small-angle neutron scattering (SESANS) device built at the VVR-M reactor at the St. Petersburg Institute of Nuclear Physics (Gatchina) are presented. SESANS utilizes the possibilities of the spin-echo method for determining the structural characteristics of materials in real space with on the 10–10⁴-nm length scale. Validation measurements are conducted using SiO₂ colloidal particles. Samples of SiO₂ spheres with a diameter determined through scanning electron microscopy and synchrotron-radiation ultra-small-angle scattering are used for calibration of the device. Approximation of the data obtained with the SESANS device was conducted using the autocorrelation function for dilute monodisperse spheres. The sizes of the spheres determined via SESANS are in agreement with those determined by other methods within the experimental error.     

Magnetic flux distribution in type II superconductors with large demagnetization and a high edge barrier

The trapped flux distribution in thin wafers of both polycrystalline and granular superconductors having large demagnetization and edge barriers of different heights is measured by means of polarized neutrons. It is shown that the nature of the critical state in polycrystalline wafers, unlike that in a ceramic wafer, is not described by the Bean model. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 12, 771–775 (25 December 1999)     

Investigation of the closed porosity of functional ceramic materials by spin-echo small-angle neutron scattering

The closed porous structure in ceramic materials is investigated by spin-echo small-angle neutron scattering. A series of ceramic samples of oxygen–ion conductors based on bismuth molybdate with the general formula Bi_12.8 X _0.2Mo₅O_{34 ± δ} (X = Mg, Ba, Ca, Sr) is obtained by powder sintering for 6?45 h at a temperature close to the melting point. The samples are characterized by scanning electron microscopy and X-ray fluorescence analysis. It is found that they had a stoichiometric chemical composition, are singlephase, and contain clean pores between crystal grains. The pore size is determined by spin-echo small-angle neutron scattering and ranges from 2.2 to 3.5 μm. It is demonstrated that longer sintering times correspond to larger pores (the increase in their average diameter is as large as 30%). It is found that the studied materials lack a fractal pore structure.     

Neutron Guide System for Ultracold and Cold Neutrons at the WWR-M Reactor

Technical Physics - The results of calculation of fluxes of ultracold (UCNs), very cold, and cold neutrons at the output of neutron guides of the UCN source with superfluid helium at the WWR-M...