Electron Irradiation Induced Modification of Ferromagnetism in (Ga,Mn)As*

The ferromagnetism properties of diluted magnetic semiconductor (Ga,Mn)As firstly improved by energetic electron irradiation, through a sequence of irradiation doses. We did a systematic study of magnetization as a function of temperature and additional magnetic field. SQUID measurements demonstrate the T$_{\mathrm{c}}$ of all (Ga,Mn)As film increased from 40K to 60K after irradiation. At the same time, electron irradiation improved the crystal quality and electric properties. The irradiation process decreases the resistance by a factor of 1/2 in the range of 10K to 50K, and transforms (Ga,Mn)As samples from insulator behavior to metallic behavior. SIMS and transport measurements confirm that the rearrangement of Mn interstitials plays a key role in the improvement of ferromagnetism properties. We infer that electron irradiation paves a new path to room-temperature ferromagnetism of (Ga,Mn)As.