Magnetic and Microstructural Aspects of the Bulk Metallic Glassy Materials Nd 60 Fe 30 Al 10
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Magnetic and Microstructural Aspects of the Bulk Metallic Glassy Materials Nd60Fe30Al10 N. H. Dan, N. X. Phuc, V. H. Ky, N. M. Hong Institute of Materials Science, NCST, Hoang Quoc Viet Str., Hanoi, Vietnam N. Chau, N. H. Luong, C. X. Huu Center for Materials Science, Department of Physics, Hanoi National University, Nguyen Trai Str., Hanoi, Vietnam. R. W. McCallum, M. J. Kramer, A. S. O’Connor, K. W. Dennis Ames Laboratory, USDOE and Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011, USA L. H. Lewis Materials and Chemical Sciences Division, Energy Sciences and Technology Dept., Brookhaven National Laboratory, Upton, New York 11973-5000, USA L. D. Tung International Training Institute for Materials Science, 1 Dai Co Viet Str., Hanoi, Vietnam
ABSTRACT The ferromagnetic bulk metallic glass (BMG) Nd60Fe30Al10 system exhibits extremely large coercivities at low temperature and moderate coercivities near room temperature. The magnetic hardness, as best evidenced by the onset of magnetic irreversibility, was studied in bulk suctioncast and melt-spun alloys with the nominal composition Nd60Fe30Al10. Systematic x-ray diffraction studies of the degree of crystallinity performed as a function of position within the bulk suction-cast samples is found to correlate with the variation in the room-temperature magnetic hysteresis character. X-ray diffraction data clearly shows the presence of both crystallites and amorphous material on the samples’ outmost surfaces; the amorphous phase content increases with distance into the cast sample. These results underscore the importance of solidification conditions and attendant nanophase selection, on the resultant magnetic properties of this class of alloys. INTRODUCTION The ferromagnetic bulk metallic glass composition RE60Fe30Al10 (RE=Nd or Pr) has generated considerable interest of both applied and fundamental nature by virtue of its appreciable coercivity at room temperature [1]. The presence and magnitude of this reported coercivity, up to 0.4 T at room temperature, is an apparent contradiction to the conventional understanding of the relationship between nanostructure and coercivity in nominally amorphous materials. An additional challenge associated with study of this class of materials is the difficulty of reproducing the results reported in various laboratories around the world [2-6]. This latter challenge indicates that the material preparation conditions, such as the purity of the starting materials, the prealloy state [7] and the solidification condition, all influence the U2.6.1
resultant magnetic properties. To further clarify the relationship between microstructure and magnetic properties in this class of materials, systematic studies of the position-dependent degree of crystallinity with the suction-cast rods were correlated with the room-temperature magnetic response. The considerable variation in magnetic response with degree of crystallinity underscores the importance of solidification conditions, and attendant nanophase selection
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