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Mean Field Analysis of Exchange Coupling in Amorphous REFe₂-B (RE = Dy, Sm) Alloy Ribbons
이정미(J. M. Lee),정재국(J. K. Jung),임상호(S. H. Lim) 한국자기학회 2001 韓國磁氣學會誌 Vol.11 No.3
Experimental magnetization-temperature curves for melt-spun ribbons of amorphous alloys (Dy_(0.33)Fe_(0.67))_(1-x)Bx (x=O, 0.05, 0.1, and 0.15) and (Sm_(0.33)Fe_(0.67))_(1-x)Bx (x=O, 0.01, 0.02, and 0.03) (in atomic fraction) are fitted with theoretical equations based on the mean field theory in order to calculate exchange couplings between constituent elements as a function of the B content. In the case of the DyFe₂-B system, the sign of the exchange coupling between Dy and Fe is negative, indicating that the magnetization direction of Dy is anti parallel to that of Fe. The sign of the other two couplings are positive indicating a parallel alignment. The exchange coupling between Fe ions are greatest, while that between Dy ions is negligible. In the case of the SmFe₂-B alloys, the sign of all the couplings are positive, indicating ferromagnetic coupling between the spins. The exchange couplings between Fe ions, and Fe and Sm are comparable to each other, but they are much greater than that between Sm ions. The high exchange coupling between Fe and Sm, which is considered to occur indirectly, is rather unexpected, but it is considered to be unique characteristics of amorphous Sm-Fe alloys. In both alloy systems, the exchange coupling between Fe ions increases with increasing B content, and this may be explained by the increase of the Fe-Fe separation with increasing B content. The exchange coupling between Fe and RE also increases with increasing B content. As the B content increases, the magnetization decreases over the whole temperature range, and the Curie temperature also decreases.