Recent developments in sputtering techniques allow the fabrication of multilayers with a high degree of perfection over large areas. We show, that using reactive sputtering, it is possible to adjust the index of refraction for neutrons, ni, of the individual layers. This property is particularly important for polarizing mirrors, where nnm for the non-magnetic layers can be matched to nm of the magnetic layers such that neutrons for one spin-eigenstate are not reflected by the coating, whereas the reflectivity is high for the other spin-eigenstate. In addition, by using anisotropic sputtering conditions it is possible to orient the easy axis of magnetization within the plane of the mirrors in any particular direction resulting in a simultaneous appearance of a pronounced remanence and coercivity. Remanent polarizers can be used as broad band spin selectors at continuous and in particular at pulsed neutron sources thus eliminating the need of spin flippers, whose performance depends on the wavelength of the neutrons and is often strongly influenced by stray magnetic fields from the sample environment. The possibility to operate remanent supermirrors in arbitrary small fields leads to attractive applications of polarizing devices in low field environments such as they occur in neutron-spin-echo or in spin selective neutron guides. We present applications, where several tasks like polarizing, focusing and spin selection are performed in one single device thus reducing the problem of phase space matching between different neutron optical components.

Applications of remanent supermirror polarizers

Internal dynamics in colloidal PNIPAM microgel particles immobilised in mesoscopic crystals

The magnetic field configuration of the spectrometer SPAN allows simultaneous NSE measurements to be performed over a particularly large angular range. The NSE precession field is created by three pairs of coils with diameters 1, 3 and 4.8 m, respectively, and the set-up has a symmetry axis, which is perpendicular to the scattering plane and crosses the sample position. The resulting magnetic field integral does not change with the scattering angle and thus fulfils the condition for multidetector NSE. In order to preserve the symmetry of the magnetic field, remanent supermirrors are used as analyzers. These supermirrors perform in reflection, in the stray magnetic field of the precession coils, and are mounted on analyzer frames with an angular opening of 25.7° each. The neutron optical elements (analyzer, polarizing guide) of SPAN have a high transmission over a large wavelength band. As a consequence of this, NSE can be done for incident wavelengths ranging from 2.5 to 9 A. At the lowest wavelengths high q values can be reached, which were not previously accessible for NSE experiments (at λ=3 A: 0.08 A−1⩽q⩽4 A−1).

Wide angle NSE: the multidetector spectrometer SPAN at BENSC

We have built a neutron resonance spin echo (NRSE) spectrometer with two secondary spectrometer arms, in order to double the solid angle of detectable neutrons. NRSE is well adapted for building up a multi-detector spectrometer, because it needs only compact magnetic coils. Compared to neutron spin echo (NSE), stray fields are much less important and can be suppressed completely by means of mumetal shielding. The second arms of the spectrometer are designed identically and allow for measuring at two different q -values simultaneously. By varying the radio frequency (RF) in the range 30–780 kHz, spin echo times up to 10 ns are achievable. Small spin echo times down to 1 ps are realized by means of additional NSE coils within the zero field regions. The instrumental resolution has been determined using a standard elastic scattering sample, and the function of the spectrometer is demonstrated by measuring diffusive dynamics in a protein solution.

RESEDA : The new resonance spin echo spectrometer using cold neutrons at the FRM-II

Polarized neutron imaging has recently been introduced as an efficient method to three-dimensionally visualize and measure magnetic fields even in the bulk of massive objects. Here we introduce a spin-echo approach for polarized neutron imaging, which has the potential to overcome some drawbacks of the first attempts, namely to deal with strong fields, arbitrary field directions and quantification. Furthermore our novel approach increases the efficiency of quantitative studies due to relaxed monochromatisation requirements for spin-echo neutron imaging and with respect to additional information available in the recorded images, which allows for straightforward quantification in many cases.

Polarized neutron imaging: A spin-echo approach

The neutron spin–echo spectroscopy (NSE) precession field, which is created by three pairs of coils with diameters 1, 3 and 4.8 m, respectively, is the peculiarity in the design of SPAN. Each pair is mounted in a Helmholtz-like fashion, with the electric currents oriented oppositely to each other, one coil above and one coil below the horizontal scattering plane. The centers of all coils are placed on the same vertical axis, which crosses the sample position. The NSE field is horizontal with axial symmetry. Particular care has been taken to shape the magnetic field around the sample, which is weak, vertical and very homogeneous. We present a first series of NSE measurements, which show that only little field adjustment is required to satisfy the exact echo condition (phase) simultaneously for a range of scattering angles and confirm the high axial symmetry of the precession field. The results show that the new magnetic field configuration of SPAN allows for multidetector NSE over a wide angular range.

Performance of the multidetector NSE spectrometer SPAN at BENSC

The peculiarity in the design of SPAN is in the NSE precession field, which is created by three pairs of coils with diameters 1, 3 and 4.8 m, respectively, and allows for simultaneous NSE measurements over a wide angular range. The experimental results confirmed the high axial symmetry of the precession field and show that the new magnetic field configuration of SPAN is particularly appropriate for multidetector NSE over a wide angular range.

The novel multidetector neutron spin echo spectrometer SPAN at BENSC

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Performance of the multidetector NSE spectrometer SPAN at BENSC

The novel multidetector neutron spin echo spectrometer SPAN at BENSC