The local structure is a term in nuclear spectroscopy that refers to the structure of the nearest neighbours around an atom in crystals and molecules. E.g. in crystals the atoms order in regularly on wide ranges to form even gigantic highly ordered crystals. However, crystals in reality are never perfect and have impurities or defects, which means, that a foreign atom resides on a lattice site or inbetween lattice sites. These small defects and impurities cannot be seen by methods such as X-ray diffraction or neutron diffraction, because these methods average in their nature of measurement over a large number of atoms and thus are insensitive to effects in local structure. Methods in nuclear spectroscopy use specific nuclei as probe. The nucleus of an atom is about 10,000 to 150,000 times smaller than the atom itself. It experiences the electric fields created by the atom's electrons that sourround the nucleus. In addition, the electric fields created by neighbouring atoms also influence the fields the nucleus experience. The interactions between the nucleus and these fields is called hyperfine interactions that influence the nucleus' properties. The nucleus therefore becomes very senstive to small changes in its hyperfine structure, that can be measured by methods of nuclear spectroscopy, such as e.g. nuclear magnetic resonance, Mössbauer spectroscopy, and perturbed angular correlation. With the same methods, the localmagnetic fields in a crystal structure can also be probed and provide a magnetic local structure. This is of great importance for the understanding of defects in magnetic materials, which have wide range of applications such as modern magnetic materials or the giant magnetoresistance effect, that is used in materials in the reader heads of harddrives. Research of the local structure of materials have become an important tool for the understanding of properties especially in functional materials, such as used in electronics, chips, batteries, semiconductors, or solar cells. Many of those materials are defect materials and their specific properties are controlled by defects.
