Room temperature L1₀ phase transformation in binary CoPt nanostructures prepared by focused-electron-beam-induced deposition.

CoPt-C binary alloys have been fabricated by focused-electron-beam-induced deposition by the simultaneous use of Co₂(CO)₈ and (CH₃)₃CH₃C₅H₄Pt as precursor gases. The alloys are made of CoPt nanoparticles embedded in a carbonaceous matrix. TEM investigations show that as-grown samples are in an amorphous phase. By means of a room temperature low-energy electron irradiation treatment the CoPt nanoparticles transform into face-centered tetragonal L1₀ nanocrystallites. In parallel, the system undergoes a transition from a superparamagnetic to a ferromagnetic state at room temperature. By variation of the post-growth irradiation dose the electrical and magneto-transport properties of the alloy can be continuously tuned.