MAGNETIC EVIDENCE FOR STRUCTURAL-PHASE TRANSFORMATIONS IN FE-CO ALLOYNANOCRYSTALS PRODUCED BY A CARBON-ARC

In previously reported work FexCo1-x[C] (x=0.0, 0.2, 0.4, 0.5, 0.6, an d 0.8 nominally) nanoparticles were prepared by a Kratschmer-Huffman c arbon-arc method. Fe0.5Co0.5[C] exhibited the largest magnetizations h eretofore observed in similarly produced nanoparticles. Here we presen t a more detailed study of the magnetic properties of Fe0.5Co0.5[C] na nocrystals. Magnetic hysteresis loops have been measured to temperatur es exceeding 1050 K. This is attributed to rotational processes in mon odomain particles and is shown to be sensitive to ordering of the part icles. Low-field thermomagnetic data clearly show features which we at tribute to the alpha-->alpha' disorder-order and alpha-->gamma phase t ransformations, respectively. (C) 1997 American Institute of Physics.