Magnetic properties and ordering in C-coated FexCo1-x, alloy nanocrystals

被引:81
作者
Turgut, Z [1 ]
Scott, JH [1 ]
Huang, MQ [1 ]
Majetich, SA [1 ]
McHenry, ME [1 ]
机构
[1] Carnegie Mellon Univ, Dept Mat Sci & Engn, Pittsburgh, PA 15213 USA
关键词
D O I
10.1063/1.367922
中图分类号
O59 [应用物理学];
学科分类号
摘要
C-coated FexCo1-x (x = 0.50, 0.45, 0.30, 0.35, 0.30, 0.25) nanoparticles were produced using a rf plasma torch. The only C source was acetylene used as a carrier gas. Structural determination by x-ray diffraction indicated a single disordered bcc alpha-FeCo phase along with graphitic C for all compositions. A Scherrer analysis of the peak widths revealed particles to have an average diameter of 50 nm. A broad log-normal size distribution was found from transmission electron microscopy observations. Magnetic hysteresis loops have been measured to temperatures exceeding 1050 K and revealed relatively high room temperature coercivities (200-400 Oe), with a strong compositional variation similar to that observed in bulk alloys. Larger coercivities are consistent with particles near the monodomain size for these alloys. The temperature dependence of the magnetization revealed the effects of atomic ordering. The variation of the saturation magnetization as a function of temperature showed a discontinuity near the bulk order-disorder (alpha-alpha') transformation temperature, as well as loss of magnetization at the alpha --> gamma structural phase transition temperature. Other features of M(T) near 500-550 degrees C are consistent with prior observations of a "550 degrees C structural anomaly" which has been observed in bulk alloys with less than perfect order. (C) 1998 American Institute of Physics. [S0021-8979(98)28711-1].
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页码:6468 / 6470
页数:3
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