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The grain boundary diffusion (GBD) process is an effective process for enhancing the coercivity of Nd–Fe–B sintered magnets. When the GBD process is applied to a thick magnet, the magnet exhibits a coercivity distribution. Partial coercivity at the centre is the same as that of the original magnet, but the partial coercivity increases on going towards the magnet surface. In this paper, the effects of conditions of the GBD process on the characteristics of coercivity distributions were investigated. Surface coercivities increase with increasing amount of coatings, while diffusion depths are almost the same. The diffusion treatment temperature varied from 800 to 900 °C, and does not affect the coercivity distributions. A long-time diffusion treatment is effective in enhancing the inner coercivities, but a very long treatment causes a significant reduction in surface coercivity.

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Rare earth magnetsPermanent magnets have improved with regard to performance dramatically over the last fi ve decades and they have become essential in modern life and industry. Thus, our lives depend directly or indirectly on the function of permanent magnets.The permanent magnets, which are currently used in various kinds of industrial equipment, are approximately divided into two categories: the ferrite magnet and the rare earth magnet. Ferrite magnets are oxide magnets composed of mainly ferric oxide. Although they do not have excellent magnetic properties, they are produced in large quantities worldwide because of their low cost and consequently have good cost performance.In contrast, despite the relatively high cost, nowadays rare earth magnets are widely used in various high-performance devices due to their superior magnetic properties. The strength of rare earth magnets exceeds those of ferrite magnets by approximately 10-fold, but the price is also approximately 10-fold that of ferrite magnets. Accordingly, as far as the cost performance of the magnet itself is concerned, there is no meaningful difference between these two types of magnets. It is expected, however, that the overall performance of equipment, for example cost reduction by downsizing of the equipment or reduction of power consumption by improving of the energy effi ciency, can be improved. The rare earth magnets are indispensable in the design of products that realize miniaturization, high performance and energy saving. Nd magnetsRare earth magnets are divided into two categories, that is, the SmCo-type rare earth magnets and the NdFeB-type magnets (hereinafter referred to as Nd magnets). With regard to current production, more than 98% of the rare earth magnets are the Nd magnets; it can be said that a rare earth magnet is synonymous with an Nd magnet. In addition, there are two types of the Nd magnets: sintered magnets and bond Thematic ReviewRare Earth Magnets: Conservation of Energy and the Environment Takehisa M inowa Magnetic Materials Research Center, Shin-Etsu Chemical, Echizen, Fukui, Japan AbstractRare earth sintered magnets (Nd magnet) have been used in many applications such as computer and industrial equipment, automobile manufacturing and many others. They are highly effi cient and reduce energy consumption because of their superior magnetic properties. The element dysprosium (Dy) contained in the Nd magnet is important and indispensable. It improves the stability of the Nd magnet by enhancing the coercive force of its magnetic properties at high temperature. Dy is not so abundant. The rapid growth of the Nd magnet may result in Dy shortage. Exploration for new deposits of Dy is desired.