Structure and magnetic properties of Zr-doped nanocrystalline Sm2Fe15Ga2Cxribbons

The phase formation and magnetic properties of melt-spun Sm2Fe15Ga2Cx ribbo ns with a Zr addition of 1.5 at. % have been investigated. A metastable pha se with the disordered TbCu7-type structure is formed in the samples anneal ed at temperatures between 620 and 740 degrees C. Upon heating above 750 de grees C, a structural transformation from the hexagonal TbCu7- to the rhomb ohedral Th2Zn17-type structure occurs. It was found that the Zr addition im proves the thermal stability of the TbCu7 structure. Transmission electron microscopy observations show that the grain sizes in 1:7-type ribbons are m uch smaller than that in 2:17-type samples. The highest value of the maximu m energy product of 88.7 kJ/m(3) is obtained in a 1:7-type ribbon annealed at 740 degrees C for 15 min. The corresponding remanence and coercivity amo unts to 0.8 and 0.43 T, respectively. In contrast, coercivities higher than 0.8 T obtained in 2:17-type ribbons are accompanied by remanences lower th an 0.66 T. The 1:7-type ribbons with grain sizes in the range of 15-45 nm s how significant remanence enhancement which can be attributed to the exchan ge coupling between adjacent grains. (C) 1999 American Institute of Physics . [S0021-8979(99)02018-6].