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 (MR) 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. 
H. Kato, K. Hamaya, Y. Kitamoto, T. Taniyama, and H. Munekata