Selforganization of Co and Fe nanoparticles in annealing process and their magnetic properties

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The present study investigated the spontaneous formation of nano-scale cobalt and iron particles in copper matrices, using Lorentz microscopy, high-resolution TEM, EELS analysis and SQUID measurements.1) Spherical iron, cobalt and iron-cobalt particles are formed at the initial stages of the precipitation. Although the spherical cobalt particles are transformed into cubic particles, iron particles have a less tendency to evolve in the shape, during the annealing.2) Iron nano-particles also make a pair-wise couplings, but the couplings were more ambiguous than Co pairs. On the contrary, spherical iron-cobalt complex particles are arranged along <100> orientations of copper matrices.3) The specimens receiving a short annealing shows a cusp at 40K, but they have another cusp around at 120K.4) Lorentz microscopy shows that the magnetic moment of the particles are oriented to 100 of copper matrices. The magnitudes of the moments are increased with the sizes, but there seem a critical size switching from fcc to bcc in structure.