Microstructural characterisation of the mechanically alloyed Cu88Fe12 and Cu72Co28 compounds and of the ball milled Cu80(Fe0.3Co0.7)20 pseudo-alloy

The effects of milling intensity and post-annealing on the microstructure of the compound Cu-80(Fe0.3Co0.7)(20) have been studied. This material exhibits giant magnetoresistance (GMR) properties, which depend strongly on the size of the magnetic particles and the distance between them. It has been prepared from mechanically alloyed solid solutions of Cu88Fe12 and Cu72Co28 powders. The powders have been characterised using thermal analysis and electron microprobe analysis. Neutron powder diffraction has been used to follow the crystallite size and the cell parameter of the Cu matrix and of the magnetic particles. Small Angle Neutron Scattering (SANS) experiments performed under saturating magnetic field allowed the characterisation of the magnetic particles. The magnetic properties of the particles have been studied through magnetisation measurements using a SQUID magnetometer. Preliminary results showed that for the binary compounds, after milling at 303K, a spin glass-like behaviour was superimposed on a small ferromagnetic signal. This proves that nearly all the iron and cobalt atoms form a solid solution with copper. The ferromagnetic volume fraction of the ternary compound is very small after milling (0,1%). It reaches 10% after annealing at 773K for 4h. This is lower than the expected precipitated volume fraction (20%). It does not seem to depend on the milling intensity.