Neutron Decoherence Imaging for Visualizing Bulk Magnetic Domain Structures

Here we introduce a novel neutron imaging method, which is based on the effect that the spatial coherence of the neutron wave front can be changed through small-angle scattering of neutrons at magnetic domain walls in the specimen. We show that the technique can be used to visualize internal bulk magnetic domain structures that are difficult to access by other techniques. The method is transferable to a wide variety of specimens, extendable to three dimensions, and well suited for investigating materials under the influence of external parameters, as, e.g., external magnetic field, temperature, or pressure.

Figure 1

Neutron grating interferometer. (a) Setup with a source grating $G0$, a phase grating $G1$, and an analyzer absorption grating $G2$. (b) Through the Talbot effect a linear periodic fringe pattern is created behind $G1$ in the plane of $G2$. (c) Intensity modulation detected in a detector pixel when one of the gratings is scanned along $x_g$.

Figure 2

Results obtained for a (100)-oriented FeSi test sample. (a) Conventional neutron transmission image (normalized to the empty beam). (b) Intensity oscillations for two detector pixels extracted from a series of eight images taken at different values of $x_g$. (c) Neutron decoherence image (DCI) of the same sample (normalized visibility, see text). (d) Corresponding magneto-optical Kerr effect (MOKE) image of a section of the disc, showing the surface domain structure.

Figure 3

Neutron decoherence images of the (100)-oriented FeSi single-crystal disc as a function of a horizontally applied external magnetic field. See also Ref. 24 for an animated series of the magnetization process.

Figure 4

Small-angle neutron scattering results of the (100)—oriented FeSi single-crystal disc. (a) Scattering pattern without an external magnetic field (logarithmic color scale). (b) Scattering pattern with a horizontally applied external magnetic field of $B=60\mathrm{mT}$ (logarithmic color scale). (c) Profiles through the scattering patterns without and with the external magnetic field as a function of the scattering angle $2\theta$.