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The propagation of neutrons in the middle layer of a planar waveguide, which is a three-layer thin film, has been studied. Neutrons emitted from the end of the film in the form of a narrow divergent microbeam have been detected. The neutron channeling length has been measured experimentally as a function of the width of the waveguiding layer. The experimental results are compared with calculations.

Neutron planar waveguides are focusing devices generating a narrow neutron beam of submicron width. Such a neutron microbeam can be used for the investigation of local microstructures with high spatial resolution. The essential parameter of the microbeam is its angular width. The main contribution to the microbeam angular divergence is Fraunhofer diffraction on a narrow slit. We review and discuss various ways to characterize the angular divergence of the neutron microbeam using time-of-flight and fixed wavelength reflectometers., 17 pages, 16 figures. Submitted to NIM A

International audience; We describe the Compact Accelerator-based Neutron Source SONATE which we are aiming for to replace the close Orphée reactor at Saclay, France. The SONATE source would serve an instrumental suite of about 10 instruments. The instruments would be split into low resolution instruments and higher resolution instruments. Our reference design is based on a proton accelerator operating at an energy in the range 20-30 MeV. The accelerator would serve 2 target stations. The first one operating at 20Hz with 2ms long pulses serving low resolution instruments (SANS, reflectivity, imaging, spin-echo) and the second one operating at 100Hz, 200µs long pulses serving higher resolution instruments (powder diffraction, Direct Time-of-flight spectroscopy, Indirect geometry spectroscopy). The 2 operation modes would be interlaced. The peak current on the target is aimed at 100 mA with an average power on the target on the order of 50-80 kW. Numerical Monte-Carlo simulations show that we may expect instrument performances equivalent to the current instruments around Orphée or ISIS.

The channeling of neutrons in a three-layer planar waveguide with a neutron-optical potential well is studied. Neutrons incident on a sample surface, which propagate in a middle layer and escape from the waveguide end in the form of a narrow divergent beam, are detected. The decay parameter of a neutron wave inside the waveguide is measured as a function of the potential well depth. Experimental results are compared with a theory.

The propagation of neutrons in the middle layer of a planar waveguide in the form of a three-layer thin film has been investigated. The microbeam from the end face of the film has been registered. The neutron channeling length has been measured as a function of the thickness of the upper waveguide layer and the resonance order. The experimental data have been compared with theoretical results.

Neutron planar waveguides produce a narrow neutron beam of submicron width which can be used to scan local microstructures with high spatial resolution. The important parameter of a planar waveguide is the distance over which the neutron wave density decays exponentially during the neutron channeling inside a guiding layer. We review various ways to experimentally characterize neutron channeling lengths. Experimental results are presented and advantages and drawbacks of the different methods are discussed.

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.

The application of a neutron microbeam to the investigation of an internal magnetic microstructure has been demonstrated experimentally. The object of investigation is an amorphous magnetic wire 190 μm in diameter, with the axial and circular magnetic domains formed inside it. A narrow neutron microbeam with a width of 2.6 μm, which is formed by a three-layer film (a planar waveguide) serves as the probe for scanning with a high spatial resolution. The method of investigation is the neutron spin precession upon transmission through the sample. © 2014 Pleiades Publishing, Ltd., This study was supported by the IMAMINE 2010-09T project (France).

In neutron waveguides, the neutron wave is confined inside the guiding layer of the structure and can escape from the layer edge as a microbeam. The channeling within the guiding layer is accompanied by an exponential decay of the neutron wave function density inside the waveguide. Here, we report direct determination of the corresponding decay constant, termed the neutron channeling length. For this, we measured the microbeam intensity as a function of the length of a neutron absorbing layer of variable length placed onto the surface of a waveguide structure. Such planar neutron waveguides transform a conventional neutron beam into an extremely narrow but slightly divergent microbeam, which can be used for the investigation of nanostructures with submicron spatial resolution.

We propose waveguide structures which transform an incident unpolarized beam into a polarized microbeam and also can be used as spin-flippers by varying the incidence angle on the structure. We describe optimized structures combining these functions. Such waveguides could be used for the investigation of one-dimensional magnetic structures and could be implemented on any existing fixed wavelength reflectometer.

The different Zeeman beam-splitting effects in neutron reflectivity experiments in reflection and refraction are discussed. Different possible representations of the experimental Zeeman splitting data in various coordinate systems are investigated. Some of these representations are useful to unambiguously identify the off-specular splitting arising from Zeeman energy and discriminate it from the usual diffuse scattering. Some representations are more suited for the direct extraction of quantitative information about the systems by using the Zeeman splitting effect. The Zeeman splitting can thus be used as a tool rather than being treated as a parasitic effect. Parameters such as the optical and magnetic potentials of buried layers can be directly extracted. The magnetic induction in demagnetized samples can also be probed. These representative characteristics are illustrated by experimental data measured on different systems. In thick AlSiFe films (20 µm), the magnetic induction is determined at the top and bottom interfaces. In thin Co layers (250 nm), the magnetic induction of ferromagnetic domains in the demagnetized state is evaluated.

A neutron waveguide is a three-layer structure in which a guiding layer with low optical potential is placed between two cladding layers with high optical potential. Under proper operation conditions, the neutron density is resonantly enhanced inside the guiding layer. In our experimental scheme, the neutron beam enters through the surface of the top layer at glancing angle and goes out from the edge of the guiding layer, with an angular distribution corresponding to Fraunhofer diffraction from a narrow slit. The incident neutron beam is relatively wide (0.1 mm) and highly collimated (0.01°). The outgoing sub-micron beam is extremely narrow at the outlet (0.1 μm) and more divergent (0.1°). So far only the production of unpolarized sub-micron neutron beams has been reported. Here we present first experiments on polarized sub-micron neutron beams. For these studies a polarized incident beam was used and two types of magnetic waveguides were investigated: a polarizing magnetic waveguide Fe(20 nm)/Cu(140 nm)/Fe(50 nm)//glass and a non-polarizing magnetic waveguide Py(10 nm)/Al(140 nm)/Py(50 nm)//glass (Py is permalloy). The waveguide samples were characterized by polarized neutron reflectometry.

Presently, neutron reflectometers can be divided in two main classes: monochromatic and time-of-flight instruments. Both types of instruments have been optimized in the last 2 decades and allow now to measure reflectivities below 10-6 which is sufficient for most experiments. The next big step is to perform specular reflectivity measurements in matters of minutes rather than hours. In order to take this step, a significant improvement in flux must be achieved. In the past few years, several proposals have been made to radically change the way reflectometers are operated. Methods based either on space-time, energy-space or spin-space encoding have been proposed. They all have the potential to increase the flux for specular reflectivity measurements by one to two orders of magnitude. We discuss the advantages and shortcomings of these different techniques.

We demonstrate in this paper the possibilities offered by Grazing Incidence Small Angle Neutron Scattering (GISANS) for the study of solid/liquid interfaces. We present experimental results obtained by Specular Neutron Reflectivity (SNR) and GISANS on a model system made of silica nanospheres adsorbed on a silicon wafer by electrostatic interactions both at solid/air interface and solid/liquid interfaces. At the solid/liquid interface, we demonstrate that grazing incidence scattering enables to discriminate the surface and the bulk scattering. The surface structure factor derived from GISANS shows that the nanospheres are organized as a repulsive liquid system, with a surface fraction occupation consistent with values obtained by SNR. This original setup highlights a direct correlation between the structure of the silica nanospheres in solution and their organization on the surface: due to the strong electrostatic repulsions between spheres, their organization at the surface is close to the projection in 2D of the 3D organization of the nanospheres in solution.

Off-specular neutron scattering from layered resonant systems has been studied. As an example, tri-layer neutron waveguides have been investigated experimentally by neutron reflectometry. In such systems, the neutron wave function is strongly localized in the guiding layer. The resonant states in the total reflection region lead to enhanced off-specular scattering from the interface roughness. The relation between the resonant states and off-specular scattering is discussed.

The magnetic and structural properties of epitaxial Fe films grown on Si(111) are investigated by polarized neutron re. ectometry (PNR) at room temperature. The influence of different types of interfaces, Fe/Si, Fe/FeSi2 and Au/Fe on the magnetic properties of Fe films deposited by molecular beam epitaxy onto Si(111) are characterized. We observe a drastic reduction of the magnetic moment in the entire Fe film deposited directly on the silicon substrate essentially due to strong Si interdiffusion throughout the whole Fe layer thickness. The use of a silicide FeSi2 template layer stops the interdiffusion and the value of the magnetic moment of the deposited Fe layer is close to its bulk value. We also evidence the asymmetric nature of the interfaces, Si/Fe and Fe/Si interfaces are magnetically very different. Finally, we show that the use of Au leads to an enhancement of the magnetization at the interface. (C) 2008 Elsevier B.V. All rights reserved.

One of the main challenges in neutron scattering is to increase the luminosity of the spectrometers. Here, a new concept of neutron reflectometer is presented. The aim is to maximize the use of the neutrons available in the guide by performing reflectivity measurements in parallel for all wavelengths. The expected flux gains are of the order of 20–50. The proposed design combines advanced neutron optical elements such as elliptical mirrors and graded multilayer monochromators. It does not require new technological developments and can be implemented right now on existing spectrometers. The REFocus set-up would enable to perform classical specular reflectivity measurements at least 10 times faster than on existing spectrometers.

We present a compact device, which can perform the energy analysis of a white neutron beam with an energy resolution of 5–10% for wavelengths λ ranging between 0.2 and 2.5 nm. We propose that such a device could be used on neutron reflectometers in order to get rid of the disk chopper or the monochromator. Gains in flux of 1 to 2 orders of magnitude can be foreseen for specular reflectivity measurements.

International audience; A second cold neutron imaging station has been open to users at the Laboratoire Léon Brillouin. The station is designed for high resolution neutron imaging and tomography. The typical field of view is 100x100 mm2 with a spatial resolution of 100 μm. Betterspatial resolutions (∼50 μm) can be achieved when reducing the field of view down to 30x30mm2. The L/D ratio can be varied from 200 to1000with pinhole sizes ranging from 20 to7 mm. Future upgrades will provide capabilities for energy resolved measurements using either a velocity selector or a double crystal monochromator. The possibility to perform polarized neutron experiments will also be provided next year.

In the field of neutron scattering, the need for micro-sized (1-50 μm) thermal or cold neutron beams has recently appeared, typically in the field of neutron imaging to probe samples with a high spatial resolution. We discuss various possibilities of producing such micro-sized neutron beams. The advantages and drawbacks of the different techniques are discussed. We show that reflective optics offers the most flexible way of producing tiny neutron beams together with an enhanced signal to background ratio. The use of such micro beams is illustrated by the study of micrometric diameter magnetic wires., This research project has been supported by the RTRA Triangle de la Physique (project IMAMINE 2010-090 T) and by the European Commission under the 7th Framework Program through the ‘Research Infrastructures’ action of the ‘Capacities’ Program, NMI3-II Grant number 283883 on Neutron Imaging.

Being able to measure reflectivities down to 10 −8 or 10 −9 is the challenge of neutron reflectometers for the 21st century. The use of a periodic tilt of the sample, coupled with a position sensitive detector enables to perform specular reflectivity measurements on continuous neutron sources without any monochromator or chopper and thus allows intensity gains up to 10 compared to conventional reflectometers. The implementation consists in modulating the incidence angle of the beam by a periodic TilT of the sample of a few degrees at a frequency of the order of 20 Hz. At each time, the sample reflects the neutron white beam at a different angle. The reflected beam arrives at a different position on the detector. The time of flight (ToF) from the sample allows to separate the wavelengths, and as a result, the full reflectivity curve is measured in each detector cell. The duty cycle of such a reflectometer is only limited by the velocity of the sample movements and may exceed 90%. We present the first results obtained on a simplified setup (40% duty cycle) installed on the EROS reflectometer at the Laboratoire Leon Brillouin. This novel instrument provides the possibility to gain more than one order of magnitude in reflectivity which opens up the study of ultra-thin films (

Neutron reflectometry with spin analysis has allowed us to perform selective hysteresis loops of each magnetic layer in GMR spin valves. The intensities now available on reflectometers and the advances of modelling give the possibility to perform a very precise analysis of the magnetic configuration even in complex systems with five different magnetic layers. Results obtained on GMR spin valves show a rather complex behaviour of the free layer as a function of the magnetic field. The NiFe soft layer exhibits a non-homogeneous rotation which cannot be observed in transport measurements. This non-homogeneous rotation explains the necessity of a rather thick soft layer to avoid 1/f magnetic noise in GMR sensors.

SANS offers the possibility to study nanostructures of sizes ranging from 2 to 200 nm. We have explored the possibility of using SANS in a grazing incidence geometry (GISANS) in order to study magnetic nanostructures in thin films (thickness ∼50 nm). Even though the amount of material is tiny in such films (∼50 μg), working in grazing incidence allows to look at the scattered signal from in-plane magnetic nanostructures in the films. We have performed surface diffraction on magnetic nanostructures (∼100 nm in size) on a system consisting of Fe 0.5 Pd 0.5 thin films with a magnetic perpendicular anisotropy. The measurements have been performed in various magnetic field configurations. Magnetic surface diffraction can easily be observed. We present these measurements together with calculations based on a Born approximation. We discuss the information that can be extracted from such polarized neutron measurements.

Polarized small-angle neutron scattering (PSANS) experimental results obtained on arrays of ferromagnetic Co nanowires ($\phi\approx13$ nm) embedded in self-organized alumina (Al$_{2}$O$_{3}$) porous matrices are reported. The triangular array of aligned nanowires is investigated as a function of the external magnetic field with a view to determine experimentally the real space magnetization $\vec{M}(\vec{r})$ distribution inside the material during the magnetic hysteresis cycle. The observation of field-dependentSANSintensities allows us to characterize the influence of magnetostatic fields. The PSANS experimental data are compared to magnetostatic simulations. These results evidence that PSANS is a technique able to address real-space magnetization distributions in nanostructured magnetic systems. We show that beyond structural information (shape of the objects, two-dimensional organization) already accessible with nonpolarized SANS, using polarized neutrons as the incident beam provides information on the magnetic form factor and stray fields \textgreek{m}0Hd distribution in between nanowires., Comment: 13 pages, 10 figures, submitted to Phys. Rev. B

Standard polarised neutron reflectometry allows one to determine magnetic in-depth profiles in multilayer magnetic thin films. We are trying to develop methods to also obtain magnetic information in the plane of the layers by using off-specular diffraction in a reflectivity geometry, which allows to probe length scales ranging from 1 to 50 μm . We present a fully dynamical treatment of the scattering of a neutron beam on a grating at grazing incidence. We have studied several model systems consisting of magnetic gratings in the micron scale range to compare calculated and measured results.

We present results of neutron diffraction on periodic gratings. The periodicities of the gratings range from 2 to 10 μm. These experiments have been performed on the time-of-flight spectrometer EROS at the Laboratoire Leon Brillouin. We show that dynamical calculations (based on a matrix formalism) can quantitatively account for the results. Experiments have been performed on several systems (with various periodicities, materials and structures) to study the diffraction efficiency effects. We show that optimised gratings can exhibit diffraction efficiencies as high as 30% over a scattering wave-vector range 0

We present the new polarised neutron reflectometer for the investigation of surface magnetism (PRISM), which has been built at the Laboratoire Leon Brillouin. This polarised neutron reflectometer with polarisation analysis has been optimised for the study of small magnetic samples (1 cm2 range).

Specular polarised neutron reflectometry with polarisation analysis allows one to probe in-depth magnetic profiles of thin films (along the normal to the film). Off-specular reflectometry gives information about lateral structures (in the plane of the film) with typical lengthscales ranging from 5 to 100 μm. Furthermore, surface diffraction at grazing angle gives access to transverse dimensions between 10 nm and 300 nm with a resolution in that direction of a few nanometers. The combination of these three techniques applied to magnetic systems can lead to a 3D magnetic structure measurement. Such a technique is however not applicable to the study of a single magnetic dot, but it can generate unique results in several cases including patterns of domain walls in thin films with perpendicular anisotropy, arrays of magnetic dots, and patterned lines in magnetic thin films.

We are developing magnetic neutron waveguides (NWG) consisting of thin films of low-optical index sandwiched between two layers of high-optical index. In such structures, the neutron wave function is strongly localized in the guiding layer and the sensitivity to interface scattering effects is enhanced. The samples were characterized on the reflectometer HADAS (FZ Julich, Germany) by specular reflectivity and off-specular scattering for different magnetic states of the permalloy layers. We show that the waveguide structure strongly enhances the off-specular scattering.

We investigate the remagnetization behaviour of remanent polarizing supermirrors by polarized neutron reflectometry. Such a mirror can be remagnetized in a magnetic field of 30 mT. It is shown, that at lower fields, the mirror is not completely remagnetized, but the magnetization of the thinner layers can be flipped more easily than the magnetization of the thicker layers. With polarized neutron reflectometry, we are able to find out exactly how many layers are magnetized parallel and how many are magnetized antiparallel to the external field. Furthermore, information about structural and magnetic imperfections (roughness, domain formation) is available.

A new surface diffraction option has been mounted on the reflectometer EROS at the Laboratoire Leon Brillouin (LLB). The originality of the design lies in the fact that we are working in a Laue-type configuration. The sample is mounted horizontally on a goniometric table. A position-sensitive detector (PSD; 200 mm × 200 mm) can be swept around the sample in the horizontal plane. The sample is illuminated by a white beam, the Bragg diffraction angle is defined by the PSD position, the dhkl is fixed by the material then according to Bragg’s law the wavelength is selected. Time-of-flight measurements can be performed to measure the diffracted wavelength. Measurements on 1-cm2 samples show that the intensity in the surface diffraction peaks at about 0.5–1 counts s-1.Measurements have been performed on non-magnetic crystals and on a magnetic Co epitaxial thin film.

We present the characteristics and performances of the time-of-flight EROS reflectometer, located at Laboratoire Leon Brillouin (Saclay, France), which operates on the high-flux Orphee reactor. It is a versatile spectrometer with a horizontal geometry enabling air/liquid, air/solid and solid/liquid measurements. It is mostly dedicated to soft matter projects but welcomes also studies on thin solid films. It is equipped with a multi-disc chopper providing a tunable δλ/λ resolution, a collimation system with two deviating supermirrors and slits with flexible apertures allowing any given δθ/θ higher than 0.007, a large sample area, and a detector (either single tube or positioning sensitive detector). The accessible Q min is 0.0026 A−1 and the accessible Q max is 0.36 A−1 in air/solid or solid/liquid geometries and 0.21 A−1 in air/liquid geometry. The spectrometer has been upgraded during the last decade in order to reach a gain in flux of ∼ 50 from its original version. In air/solid geometry, we reach R min = 2×10−5 in 1 hour, R min = 8×10−7 in 4 hours and R min = 4×10−7 in 12 hours on a sample of ∼ 20 cm2 with EROS II, while it was difficult to go below 10−5 with the initial version dating from 1992. In air/liquid or solid/liquid geometries, we show that the main limitation to reach very low reflectivities is the incoherent scattering of the liquid solvent (D2O) . For such geometries, we obtain R min of 5×10−6 in 4 hours after incoherent background subtraction. The rejuvenated EROS allows thus measurements of 15-20 samples of a few tens cm2 in a span of 4 days, which corresponds to the minimum time allocated to external users for a given experiment.

International audience; An experimental and numerical study of the magnetization in (Fe 3 nm/Dy 2 nm) multilayers is presented. The samples were thermally evaporated under ultra-high vacuum at two different substrate temperatures, 320 and 570 K. In order to get the magnetization depth profile of these transition metal/ rare earth (TM/RE) multilayers, a fine investigation of the structural, chemical, and magnetic properties was carried out. The samples were studied by X-ray reflectivity (XRR), high resolution transmission electron microscopy (HRTEM), conversion electron Mö ssbauer spectrometry (CEMS), SQUID magneto-metry and polarized neutron reflectivity (PNR). Magnetization profiles were obtained by Monte Carlo simulations to support the PNR fits. The key role of the crystalline structure is emphasized by magnetic depth profile measurements performed using polarized neutron reflectometry. The antiparallel configuration of Fe and Dy layers' magnetizations was evidenced, as well as the perpendicular magnetic anisotropy (PMA), especially in the case of the sample prepared at 570 K.

Advanced nano-technology is exploited to produce a set of Fresnel neutron zone plates of large aperture and with similar and reproducible characteristics. These zone plates have been employed to test the performance of a stack of them. It is found that the stack of many zone plates can be effective in handling a neutron beam.

We present the operation of a matrix of Fresnel zone plates consisting of 900 individual zone plates. The individual efficiency of the zone plate lenses is close to 30% for λ =13.7 A. We discuss the use of such a matrix as an optical element for performing high-resolution neutron imaging (at a sub 50 μm resolution).

Our objective is to characterize surfaces and interfaces at the nanometric scale. This corresponds to very small volumes of matter of the order of a few micrograms. Thus, it is necessary to develop surface scattering techniques. The use of neutron reflection at grazing incidence increases the neutron interaction with the sample surface and makes such experiments feasible. It is possible to distinguish three grazing incidence scattering geometries (see Fig. 1): specular reflection, scattering in the incidence plane (off-specular scattering) and scattering perpendicular to the incidence plane. These different scattering geometries allow to probe different length scales and directions in the sample surface. Specular reflectivity (red line) allows to probe the structure along the depth in the film (3 nm ≤ ≤ 100 nm). Off-specular scattering measurements (blue plane) allows to probe in-plane surface features at a micrometric scale (600 nm ≤ ≤ 60 m). GISANS Grazing Incidence SANS (green plane) allows to probe in-plane surface features in the range 3 nm ≤ ≤ 100 nm. These different scattering geometries allow to probe a very wide range of length-scales , ranging from a few nm up to several m. Structures perpendicular and in-plane can be probed. In this chapter we will restrict ourselves to specular reflectivity. We will present the principle of the technique and some examples of measurements on real multilayer systems.

We present the new polarized reflectometer for the investigation of surface magnetism, which has been built at the Laboratoire Leon Brillouin. This polarized neutron reflectometer with polarization analysis has been optimized for the study of small magnetic samples (1 cm2 range). We describe the new multilayer monochromator which has permitted us to obtain a wider wavelength distribution (∼4%) and the focusing neutron guide which has allowed the focalization of a 100 mm high beam onto a region 15 mm high. This new optical setup has allowed a large neutron flux increase, which is now of 2×105 n/cm2 s.

Planar waveguides can transform a conventional neutron beam into a very narrow but slightly divergent microbeam. Such microbeams could be used for the investigation of nanostructures with a high spatial resolution. We have investigated the tri-layer magnetic structure Fe/Co/Fe which transforms an unpolarized incident beam into a polarized microbeam. The polarized neutron reflectometer NREX with a horizontal sample plane was used for the waveguide characterization. Some practical aspects of microbeam extraction and polarization are discussed.

We have used polarized neutron reflectivity, X-ray diffraction, X-ray reflectivity and magneto-optical Kerr effect in polar configuration to study the properties of ultrathin Pt/Co/Pt films. Structures consisting of a 5-nm thick Pt buffer, 3-nm thick Co layer and 5-nm thick Pt cover layer were deposited onto (0001)-oriented Al2O3 substrate by the molecular beam epitaxy (MBE) method. Irreversible modifications of film properties, resulting from its illumination by single femtosecond laser pulses, of duration of 40 fs and wavelength of 800 nm, were observed and analyzed. As prepared films exhibited magnetization in-plane, but after laser irradiation, the direction of magnetization was rotated to out-of-plane state. Formation of Co–Pt alloy phase caused by quasi-uniform film irradiation was demonstrated by the results of X-ray and neutron scattering measurements. Moreover, polarized neutron and X-ray reflectivity data showed that after illumination Co was distributed mostly in the area of nominal Co ...