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Since the discovery of 2:14:1 permanent magnets (PMs) in the early 80’s, the nanocrystalline and nanocomposite RE-Fe-B PMs attracted extensive attention both from the academia and industry because of their enhanced magnetic performances and potential applications (Croat et al., 1984; Givord et al.., 1984; Hadjipanayis et al., 1984; Onodera et al., 1984; Yamauchi et al., 1985; Jha & Davies, 1989; Pinkerton, 1991; Hadjipanayis, 1999; Liu et al., 2008; Fukagawa et al., 2010). Whereas the enhanced remanence and energy product of nanocrystalline NdFe-B PMs result from the exchange coupling between magnetically hard grains (Manaf et al., 1993), for the nanocomposite PMs the superior magnetic properties are the result of the fine mixture of RE2Fe14B hard magnetic and Fe-based soft magnetic grains, which are exchange coupled (Kneller & Hawig, 1991). Typically, the exchange coupling in nanophase magnets tends to reduce the coercivity (Mendoza-Suarez et al., 2000) and the energy product decreases with the volume fraction of the magnetic phase, which are well-known challenges in the processing of PMs. The recent work proved the important role played by magnetostatic interactions in the increase of the nucleation and coercive field values of nanocomposite permanent magnets in the detriment of the exchange coupled interactions (Gabay et al., 2006; Marinescu et al., 2008). The properties of nanocomposite PMs are strongly influenced by a number of process parameters like the composition, preparation method, annealing conditions, distribution of soft and hard magnetic nanograins (Cui et al., 2005). The large values of the remanence are related to the strength of the exchange interactions between the soft and hard magnetic grains, thus the reduction of the grains below the size of the hard magnetic phase domain walls is essential, but they should not decrease below a critical value, dependent on the nanocomposite composition, which causes the reduction of the magnetocrystalline anisotropy of the hard magnetic phase and, consequently, the drastic decrease of the coercive field. Nanocomposite magnets are expected to have maximum energy products as high as 120 MGOe, when the soft and hard magnetic phases are arranged in the proper way and the exchange interactions optimized (Skomski & Coey, 1993). However, the theoretical value of the maximum energy product of NdFeB magnets is calculated to be 512 kJ/m3 (64 MGOe) (Sagawa et al., 1985). There are two principal manufacturing routes to prepare RE-TM-B nanocomposite PMs: (i) the classical powder metallurgy or sintered magnet process (Sagawa et al., 1984; Durst &

Spark Plasma Sintered NdFeB-based Nanocomposite Hard Magnets with Enhanced Magnetic Properties