Regensburg 2004 – scientific programme

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MA: Magnetismus

MA 31: Spinelektronik

MA 31.3: Talk

Friday, March 12, 2004, 11:15–11:30, H22

Exchange interactions and Curie temperatures in diluted magnetic semiconductors — •P. Dederichs¹, K. Sato¹, and H. Katayama-Yoshida² — ¹IFF,Forschungszentrum Jülich, D-52425 Jülich — ²ISIR, Osaka University, Ibaraki, Osaka 567-0047, Japan

The magnetic properties of diluted magnetic semiconductors are calculated within the framework of the KKR-CPA, using a mapping on a Heisenberg model. Effective exchange coupling constants are evaluated by embedding two impurities in the CPA medium. Curie temperatures (Tc) are estimated by the mean-field approximation (MFA), the random phase approximation (RPA) and by monte carlo methods. In MFA and RPA, Tc is proportional to the square root of Mn concentration c for (Ga, Mn)N, while in (Ga, Mn)Sb Tc is linear to c. Since the extended hole states mediate the ferromagnetism in (Ga,Mn)Sb (p-d) exchange), the interaction is long range leading to a flat spin wave dispersion. Thus, the MFA gives similar results as the RPA. In (Ga, Mn)N, due to the broadening of the impurity bands in the gap, the ferromagnetic state is stabilized by double exchange. Since the impurity states are well localized, the exchange interaction is short range leading to dispersive magnon bands and the MFA values deviate from the RPA values. However the reliability of both MFA and RPA are in this case questionable.