Over the last few decades magnetism has seen an enormous expansion into a variety of different areas of research, notably the magnetism of several classes of novel materials that share with truly ferromagnetic materials only the presence of magnetic moments. Volume 21 of the "Handbook of Magnetic Materials", like the preceding volumes, has a dual purpose. With contributions from leading authorities in the field, it includes a variety of topics which are intended as self-contained introductions to a given area in the field of magnetism without requiring recourse to the published literature. It is also intended as a reference for scientists active in magnetism research, providing readers with novel trends and achievements in magnetism. Volume 21 comprises topical review articles covering Heusler compounds, quasicrystalline solids, bulk amorphous alloys and nanocrystalline soft-magnetic alloys. In each of these articles an extensive description is given in graphical as well as in tabular form, much emphasis being placed on the discussion of the experimental material within the framework of physics, chemistry and material science. It is composed of topical review articles written by leading authorities. It introduces given topics in the field of magnetism. It provides the reader with novel trends and achievements in magnetism.