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An appropriate formalism is developed which describes the effect of simultaneous occurrence of nuclear and magnetic interaction caused by an arbitrary structure of sequential magnetic domains on the emerging intensity and polarization.

We propose a new method of investigating domain structures in ferromagnetic solids which combines neutron depolarization concepts with perfect crystal neutron interferometry.

Spin-dependent bi-refringence of neutrons upon passage through the air gap of a prismatically shaped permanent magnet yoke is used to split a thermal neutron beam in two polarized sub-beams with slightly different directions. This method is ideal to polarize the neutrons within perfect crystal interferometers without loss of intensity. Using a sequential arrangement of two such prisms a splitting larger than twice the rocking-curve width of a perfect crystal Mach–Zehnder-type neutron interferometer has been achieved, yielding a beam polarization of about 97%.

We present a neutron polarimetric experiment clearly demarcating geometric and dynamical phases. Here a relative rotation between two identical π spin flippers produces a pure geometric phase and their relative translation yields a pure dynamical phase. The experiment agrees with theory to within about 1%.

An interference experiment with polarized neutrons is proposed to check the duality relation between the fringe visibility and the which-way information for massive fermions with macroscopic spatial separation of the interfering sub-beams. The connection between polarization-sensitive post-selection of sub-ensembles and the concept of quantum erasure is discussed. This neutron experiment will supplement those recently performed with photons and atoms.

The perfect crystal interferometer instrument S18 at the Institute Laue-Langevin (ILL) in Grenoble has been upgraded to allow more advanced neutron optics experiments for fundamental, nuclear and condensed matter physics. The new supermirror guide together with the multipurpose monochromator provides considerably higher intensities in a wide wavelength region. The optimal use of neutrons is obtained by a nondispersive arrangement of the monochromator and the interferometer crystals. This also allows to obtain completely polarised beams using permanent magnetic prism deflection. An additional third analyzer axis permits novel postselection experiments concerning momentum distribution and polarisation analysis of the interfering beams. Several types of large perfect crystal interferometers are available for different applications. The system can be configured as an advanced high-resolution Bonse–Hart small angle scattering camera. The results of various test measurements concerning intensities, interference contrast, long-term stability, the accessible wavelength range and the basic features as a SANS camera will be presented. Various proposals for experiments will be discussed as well.

The recently proposed neutron magnetic tomography, an extension of the three-dimensional neutron depolarization technique, is considered. The new method allows visualization of magnetic domains within bulk materials. In concept it is similar to X-ray tomography but the analysis is much more involved because of the tensorial character of neutron spin rotations. An improved iterative numerical procedure is presented which fully accounts for the non-Abelian properties of the spin rotation. The method is applied successfully to the reconstruction of domain structures from simulated data of schematic examples. The experimental feasibility is discussed.

A miniature sample rotation device has been realized that fits into a cryostat of only 20 mm diameter and allows to perform a new procedure of aligning the anisotropy axis of uniaxially anisotropic ferromagnets precisely along the neutron beam, so as to derive the relevant domain structure parameters from the observed neutron depolarization. Test measurements on NdFeB samples of known orientation of anisotropy show the feasibility of this new method.

The recently proposed implementation of the tensorial magnetic tomography concept into perfect crystal neutron interferometry is considered. The mathematical relations between the observables of neutron interference and standard depolarization experiments are given.

Neutron magnetic tomography, the recently proposed extension of the neutron depolarisation technique, is considered. The available numerical methods for the analysis of the data are reviewed and the possibility of visualising the magnetic structure within bulk materials is demonstrated by specific examples. Various ways to implement the method experimentally are presented. Estimates of the feasibility in terms of required measuring time indicate that visualisation is within experimental reach with modern neutron optical devices.