Unconventional Carrier-Mediated Ferromagnetism above Room Temperature in Ion-Implanted (Ga, Mn)P:C

Ion implantation of Mn ions into hole-doped GaP has been used to induce ferromagnetic behavior above room temperature for optimized Mn concentrations near 3 at. %. The magnetism is suppressed when the Mn dose is increased or decreased away from the 3 at. % value, or when $n$-type GaP substrates are used. At low temperatures the saturated moment is on the order of 1 Bohr magneton, and the spin wave stiffness inferred from the Bloch-law $T^{3/2}$ dependence of the magnetization provides an estimate $T_c=385\mathrm{K}$ of the Curie temperature that exceeds the experimental value, $T_c=270\mathrm{K}$. The presence of ferromagnetic clusters and hysteresis to temperatures of at least 330 K is attributed to disorder and proximity to a metal-insulating transition.