New permanent magnets

Permanent magnets play an important role and are widely spread in daily-lif e applications. Due to their very low costs, large availability of the row materials and their high chemical stability, hard ferrites are still domina nt in the permanent magnet market although their relatively poor magnetic p roperties are a distinct disadvantage. Today's high-performance magnets are mostly made from Nd2Fe14B. The aim of research is to combine the large spo ntaneous magnetization of 3d metals with strong. anisotropy fields known fr om rare-earth transition-metal compounds and, at the same time, to maintain a high value of the Curie temperature. However, the number of iron-rich ra re-earth intermetallics is very limited and, consequently, not much success can be noted in this field for the last 10 years. One alternative concept is to use magnetic fields trapped in type II superconductors where much hig her fields can be achieved compared to conventional rare-earth magnets. Ver y recently, we obtained a trapped field as high as 14.4 T in a melt-texture d YBCO bulk sample of a few centimeters in diameter. This is the highest va lue ever achieved in a bulk superconductor. The trapped field of a supercon ductor is not governed by the Laplace equation and, therefore, levitation w orks without any additional (active) stabilization. The disadvantage of the se magnets is their low working temperature (of liquid nitrogen and below). (C) 2001 Elsevier Science B.V. All rights reserved.