Local magnetic structure determination using polarized neutron holography

Abstract

A unique and important property of the neutron is that it possesses magnetic moment. This property is widely used for determination of magnetic structure of crystalline samples observing the magnetic components of the diffraction peaks. Investigations of diffraction patterns give information only about the averaged structure of a crystal but for discovering of local spin arrangement around a specific (e.g., impurity) nucleus remains still a challenging problem. Neutron holography is a useful tool to investigate the local structure around a specific nucleus embedded in a crystal lattice. The method has been successfully applied experimentally in several cases using non-magnetic short range interaction of the neutron and the nucleus. A mathematical model of the hologram using interaction between magnetic moment of the atom and the neutron spin for polarized neutron holography is provided. Validity of a polarized neutron holographic experiment is demonstrated by applying the proposed method on model systems. V C 2015 AIP Publishing LLC. [http://dx.A common property of diffraction methods is that they measure the averaged structure of the entire sample and they provide limited information on the local structure around a specific nucleus, e.g., an impurity atom. Atomic resolution holography is a special method for direct imaging of the structure around a selected atom. Holograms with atomic resolution have been recorded applying various kinds of de Broglie waves, e.g., electrons, 1 X-rays, 2 or neutrons. 3-5 These methods always need an incorporated source or a detector of the radiation inside the sample, 6 thus two types of holography can be distinguished: inside source holography (ISH) and inside detector holography (IDH). In the following, we consider only the IDH case. In this case, a part of the incoming plane wave directly reaches the detector atom and other parts of plane wave are scattered on the neighbourhood of the detector atom before reaching it. The interference pattern is recorded in the position of the detector atom by emission of a characteristic radiation. The intensity of the radiation emitted by the detector atom is proportional to the intensity of the interference pattern at the position of detector nucleus. Interference pattern is scanned by changing the sample orientation.These properties mentioned above are independent from the type of used radiation. Neutron holography is useful because neutrons have some particular properties, such as interaction with the nucleus (especially with the hydrogen nucleus), high penetration depth, and possession of magnetic dipole moment, which make them unique probes for structural studies.Neutrons interact with the magnetic moment of atoms in a crystal through the neutron spin, allowing them to carry out magnetic neutron holography (MNH). This advantage has been mentioned in Refs. 7 and 8, but no detailed study about the expected hologram was given.Cadmium, boron, and gadolinium can be effectively used as inside detector nuclei because of their rather high absorp...

Imaging local magnetic structure by polarized neutron holography

“…It was suggested earlier that the local magnetic structure can be imaged in the bulk material using the scattering of polarized neutrons on the magnetic moment of unpaired electrons [16,17]. The magnetic interference pattern of neutrons was modelled by the present authors [18] for the first time. It was found that the widely used reconstruction procedure proposed by Barton [19] can be used only in a special configuration for the reconstruction of radial magnetic spin vector components lying along the line connecting the detector nucleus and the magnetic atom.…”

“…The selection of the optimal neutron wavelength involves the consideration of two processes [18]. The first is the oscillation of the cos(kr − kr) part in eq.…”

“…The reconstructed image of the basal plane perpendicular to the ] position can be reconstructed using the Barton method [18]. These magnetic moments remain reconstructible with the correlation method with improved resolution.…”

“…Detailed theoretical work [25,26] and successful experiments [9,11,12,27] were performed using the nuclear interaction between the neutron and the nucleus. The calculation of the magnetic hologram was published in a previous article [18] and now a short summary is provided. The non-spin-flip magnetic scattering amplitude on the spin moment of an atom [28] is…”

“…The Barton method can be used to reconstruct the radial component of the magnetic moments [18] in a particular experimental arrangement when the neutron spin points along the beam direction. The corresponding interference pattern is shown in fig.…”