Nano-crystallite Fe3C with giant magnetic coercivity in SiO2

⁵⁷Fe and ¹²C ions were implanted at room temperature into single crystal SiO₂ with energies yielding approximately the same calculated ranges. The energies were 60 and 20 keV, respectively for ⁵⁷Fe and ¹²C and their corresponding doses were 5 × 10¹⁶ and 2 × 10¹⁷ at/cm². The cementite Fe₃C was formed after annealing at 650°C with a size of about 7 nm. Magnetic coercive forces of 900 and 800 Oe were obtained at RT and 80 K, respectively. An explanation for such a strong coercivity is suggested.