Effect of Ga + irradiation on magnetic and magnetotransport properties in (Ga,Mn)As epilayers

We report on the magnetic and magnetotransport properties of ferromagnetic semiconductor (Ga,Mn)As modified by Ga+ ion irradiation using focused ion beam. A marked reduction in the conductivity and the Curie temperature is induced after the irradiation. Furthermore, an enhanced negative magnetoresistance and a change in the magnetization reversal process are also demonstrated at 4 K. Raman-scattering spectra indicate a decrease in the concentration of hole carriers after the irradiation, and a possible origin of the change in the magnetic properties is discussed.