Spin glass and noninteracting nanoparticle phenomenologies in the same alloy: Magnetic monitoring of the atomic diffusion processes and implications on the microstructure

The magnetic behavior of a unique sample of ${\mathrm{Cu}}_{97.5}{\mathrm{Co}}_{2.5}$ is shown to vary from spin-glass-like, in the as-spun state, towards that of a noninteracting nanoparticle ensemble after sequential annealing treatments. This result is explained by specifically considering the role of the remaining copper-cobalt solid solution regions. In particular a progressive cobalt depletion of the nanoparticle surroundings seems to affect the effectiveness of the Ruderman-Kittel-Kasuya-Yosida interaction mechanism between the Co-rich particles. The presented explanation may also be of help in understanding the magnetic properties of other metallic alloys much beyond the copper-cobalt case.