Microstructure and properties of giant magnetoresistive granular Au80Co20 alloys

The relationship between microstructure and giant magnetoresistance (GMR) o f granular Au80Co20 was investigated. Two different processing routes were explored. With the melt spinning technique the microstructure appeared to b e so coarse that it was not expected to exhibit any substantial GMR effect. On the other hand, with the procedure of solid-solution annealing and wate r quenching afterwards, a suitable nanostructure was prepared that showed a GMR of 29% at 10 K and 50 kOe. Subsequent annealing causes coarsening of C o particles. In additional spinodal decomposition occurred for a certain te mperature range and a loss of coherency of the Co particles with respect to the Au was observed with high-resolution transmission energy microscopy. A t magnetic fields above similar to 20 kOe, all annealed alloys showed a sat urating magnetization, whereas the resistance is still steadily decreasing, challenging the presumed mathematical relationship between GMR and overall magnetization. (C) 2001 American Institute of Physics.