Nano-scale precipitates formed in Cu-Co based alloys and their magnetic properties.

The microstructural evolutions of nano-scale magnetic Co particles formed in Cu-Co base alloys have been investigated on isothermal annealing at 973 K, using transmission electron microscopy (TEM). After the solution treatment and short annealing, nano-scale magnetic particles appeared randomly in the Cu-rich matrix. With increasing the isothermal annealing time, however, pairs and sometimes more than two of Co precipitates were linearly arranged along <100> directions in Cu-Co alloys. On the other hand, such linear arrangements of precipitates were extended in Cu-Ni-Co alloys. Co precipitates were cubic in the coherent stage and octahedral in incoherent stage of precipitation in binary alloys, while the precipitates rendered rectangular shapes even in the incoherent stage in Cu-Ni-Co. The magnetic properties of the specimens have also been measured at the similar conditions, with the superconducting quantum interference device (SQUID) magnetometer. The present study revealed that coersive forces of the specimens were correlated with the microstructural evolution occurring during the isothermal annealing.