The Effect of Heat Treatment to FePt/Fe₂O₃ and FePt/Cu Magnetic Performance

The effect of heat treatment to FePt/Fe₂O₃ and FePt/Cu magnetic performance was examined in this paper. To obtain desired phase transformations for high magnetic storage media, a self-assembled layer of FePt nanoparticles was placed between two layers of Fe₂O₃ nanoparticles using surfactants on Si and Cu substrates to minimize aggregation during heat treatment. To eliminate the surfactant, a sample made by simply mixing FePt and Cu nanoparticles in hexane was deposited on a Cu substrate. Vacuum furnace annealing at 600 °C (1 h) or laser heat treatment at 20, 40, 80 W at a speed of 1–1.5 m/s were carried out on the samples. The coercivity of FePt/Fe₂O₃-layered samples increased from 148 Oe to 366 Oe and 246 Oe for furnace annealed samples on Si and Cu substrates, respectively; while, it remained almost unchanged in laser heat-treated samples on Cu substrate and slightly higher magnetization at 40 W compared to 20 W laser heat treatment of samples on Si substrate. The FePt/Cu nanoparticles mixer layer on Cu substrate was subjected to laser heat treatment at 40 and 80 W. The coercivity at both laser powers did not show any significant change. During the 80 W laser heat treatment, most of the particles escaped from the surface indicating a high temperature process. The results indicate that the furnace annealing at 600 °C brings the desired magnetic phase transformation in all cases, while the laser heat treatment even at high power does not bring the phase transformation due to very short time period for processing.