Application of the geometrical model to description of the remanence enhancement in hard magnetic RE-M nanocomposites
Waldemar Kaszuwara Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa
Annals 3 No. 7, 2003 pages 159-164
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abstract A simple geometrical model which describes enhanced remanence in nanocrystalline magnetic materials in terms of their phase constitution has been formulated. It has been assumed that in isotropic material, the remanence value which can be calculated on a basis of the Stoner-Wohlfarth model for the non interacting single domain particles, some proportion of its volume attains the properties characteristic of an anisotropic material. The magnetically aligned material ranges in the vicinity of magnetically hard crystallites, easy magnetisation axes of which are oriented parallel to the external magnetic field. The length of these exchange interactions L can be expressed by L = (A/K1)1/2 (where A - exchange constant, K1- first anisotropy constant). Contribution of this aligned material to the total remanence value of the magnet is equal to the product of its volume fraction and saturation magnetisation. The dependence of the remanence value on the rare earth content, which can be calculated on a basis of this model, exhibits three distinct parts origin of which has been explained. The calculated values of the remanence are in good agreement with the experimental data for Nd-Fe-B and Sm-Fe-N magnets prepared by mechanical alloying. Key words: hard magnetic nanocomposites, Nd-Fe-B permanent magnets