Magnet materials, rare-earth compounds

Rare earth ions have been paid much attention to for their partieular optical properties and magnetic properties. Rare earth compound have been widely used as laser materials, lumineseent materials, coloring agents of ceramics or glass and so on l The optical materials doped erbium ion have been widely investigated for this ion has abundant energy levels. The energy levels and... 

It is quite natural that not all authors and not all papers could be included in this review due to the limited amount of space and capability of the author. But since this article is not the only review and probably not the last one on this topic the problems and materials will always be illuminated from different points of view. With respect to magnetic semiconductors we want to recall that non-rare earth compounds like the Cr spinels (Haas, 1970) offer similar effects as the Eu chalcogenides. Also the group of the RE-pnictides may become ferromagnetic semiconductors with increasing purity and perfection of the samples, but at the moment their conduction mechanism is still in discussion (see also F. Hulliger, vol. 4, ch. 33 of this Handbook). 

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