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MA: Magnetismus

MA 31: Spinelektronik

MA 31.5: Talk

Friday, March 12, 2004, 11:45–12:00, H22

Which Mn is ferromagnetic in Ga_1−xMn_xAs? — •O. Rader¹, K. Fauth², G. Schott², G. Schmidt², L. Molenkamp², G. Schütz³, F. Kronast¹, and W. Gudat^1,4 — ¹BESSY, 12489 Berlin — ²Physikalisches Institut, Universität Würzburg, 97074 Würzburg — ³MPI für Metallforschung, 70569 Stuttgart — ⁴Institut für Physik, Universität Potsdam, 14415 Potsdam

The origin of ferromagnetism in the diluted magnetic semiconductor Ga_1−xMn_xAs is a matter of controversy. In spite of important contributions from electron spectroscopy, understanding the electronic structure has been hampered by an indistinguishability of Mn atoms. We combine sensitivity to atomic number, chemical shifts, and to magnetic order in a field-dependent (0-2.4 T) magnetic circular x-ray dichroism study at the Mn L-edge and observe three constituents of distinct magnetic behavior. We find that ferromagnetic Mn deviates more strongly from a 3d⁵ configuration than assumed previously, that superparamagnetic clusters of 20µ_B are formed, and that interstitial Mn, previously considered the key to highest T_C’s, does not contribute to the ferromagnetism.