High heat generation ability in AC magnetic field of nano-sized superparamagnetic Y_3Fe_5O_(12) ferrite powder prepared by physical bead milling

摘要

Nano-sized superparamagnetic Y_3Fe_5O_(12) ferrite having a high heat generation ability in an AC magnetic field was prepared by physical bead milling. The highest heat ability in the AC magnetic field was for the fine Y_3Fe_5O_(12) powder with a 16-nm crystallite size (the samples were milled for 4 h using 0.1 mmφ beads). The main reason for the high heat generation property of the milled samples was ascribed to an increase in the Neel relaxation of the superparamagnetic material. For the samples milled for 4 h using 0.1 mmφ beads, the heat generation ability (W·g~(-1)) was estimated using a 3.58 × 10~(-4)·f·H~2 frequency (f/kHz) and the magnetic field (H/kA·m~(-1)), which is the highest reported value of superparamagnetic materials. Furthermore, Y_3Fe_5O_(12) microspheres having a 20-32 μm diameter range were prepared by a spray dryer using the bead-milled nano-sized particles.