Visualization of magnetic domains and magnetization processes in bulk materials by neutron dark-field imaging

C. Grunzweig (Paul Scherrer Institut, Switzerland)

Magnetic domains and their substructures form the link between the basic physical properties of a magnetic material and its macroscopic characteristics. Today a range of experimental techniques exists for the observation of surface domains and for the investigation of domains in thin film samples, provided they are transparent for electrons or X-rays. Due to the limited penetration depth of the used radiation, the investigation of domain structures is restricted to the sample surface and to thin film samples. The investigation of magnetic domains in bulk ferromagnetic materials remains a significant challenge. Neutrons can easily penetrate centimeter thick metallic samples and interact through their spin directly with the local magnetization. Therefore researchers utilize this advantage to investigate domain structures in bulk materials.

Here we present a new method for the study of bulk ferromagnetic domain structures. This technique overcomes some of the drawbacks that challenge other neutron imaging methods, in Terms of exposure times and image quality. The technique is based on a neutron grating interferometer [1]. The field of view of the setup is 64 x 64 mm2 and the spatial resolution is about 100 µm. The image contrast relies on the effect that the spatial coherence of the neutron wave front can be changed through small-angle scattering of unpolarized neutrons at magnetic domain walls in the specimen [2]. The measured scattering image is termed `neutron dark-field image'' (nDFI).

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