The nature and origin of ferromagnetism in magnetic semiconductors is investigated by means of highly precise electronic and magnetic property calculations on MnxGe1-x as a function of the location of Mn sites in a large supercell. Surprisingly, the coupling is not always ferromagnetic (FM), even for large Mn-Mn distances. The exchange interaction between Mn ions oscillates as a function of the distance between them and obeys the Ruderman-Kittel-Kasuya-Yosida analytic formula. The estimated Curie temperature is in good agreement with recent experiments, and the estimated effective magnetic moment is about 1.7 µB/Mn, in excellent agreement with the experimental values, (1.4–1.9) µB/Mn.

Ferromagnetism in Ⅰ-Ⅲ-Ⅵ2 chalcopyrite semiconductors is predicted to arise from holes provided by Mn doping in the illustrative case of CuGaSe2. The first-princi plescalculations within the generalized gradientapproximation to density functional theory demonstrate that Mn substitutes for Ga sites in CuGaSe2 with a formation energy that is～0.25 eV lower than that for Cu sites. Ferromagnetic CuGa1-xMnxSe2 is found to be a half-metallic material with a magnetic moment of 4 µB per Mn for x≥0.25, and its estimated Curie temperature is more than 110 K. We suggest that higher Curie temperatures may be achieved for this new class of ferromagnetic semiconductors based on Mn-doped Ⅰ-Ⅲ-Ⅵ2 chalcopyrites by employing other materials with a smaller lattice constant such as CuGaSe2 and CuAlSe2.

Recently reported room-temperature ferromagnetic（FM）semiconductors Cd1-xMnxGeP2 and Zn1-xMnxGeP2 point to a possible important role of Ⅱ-Ⅳ-Ⅴ2 chalcopyrite semiconductors in “spintronic” studies. Here, structural, electronic, and magnetic properties of （i） Mn-doped II-Ge-VI2 (Ⅱ= Zn or Cd and V=P or As）chalcopyrites and（ii）the role of S as impurity in Cd1-xMnxGeP2 are studied by first-principles density functional calculations. We find that the total energy of the antiferromagnetic（AFM）state is lower than the corresponding FM state for all systems with Mn composition x=0.25, 0.50, and 1.0. This prediction is in agreement with a recent experimental finding that Zn1-xMnxGeP2 experiences a FM to AFM transition for T less than 47 K. Furthermore, a possible transition to the half-metallic FM phase is predicted in Cd1-xMnxGeP2 due to the electrons introduced by n-type S doping, which indicates the importance of carriers for FM coupling in magnetic semiconductors. As expected, the total magnetic moment for the FM phase is reduced by one mB with each S substituting P.

Ga1-xMnxAs and related semiconductors are under intense investigation for the purpose of understandingthe ferromagnetism in these materials, pursuing higher TC, and, finally, for realizing semiconductor electronic devices that use both charge and spin. In this work, the electronic and magnetic structures of Ga1-xMnxAs (x＝3.125%, 6.25%, 12.5%, 25.0%, 50.0%） are studied by first-principles full-potential linearized augmented plane wave calculations with the generalized-gradient approximation. The ferromagnetic state is lower in energy than the paramagnetic and antiferromagnetic states. It is confirmed that Mn atoms stay magnetic with well localized magnetic moments. The calculated band structure shows that Mn doping also forms defect bands, and makes（Ga,Mn）As p-type conducting by providing holes. Furthermore, an s-d population inversion is found in the Mn electronic configuration, which results from the strong Mn p-d mixing. The induced As moments are substantial（about 20.15µB per Mn atom, and almost independent of x)—in accord with a recent observed negative As magnetic circular dichroism signal.

The recently reported room-temperature ferromagnetism in Cd1-xMnxGeP2 was investigated for x＝1.0,0.5, and 0.25 by the local density first-principles full-potential linearized augmented plane wave（FLAPW）and DMOL3 methods within both local-density approximation（LDA）and generalized gradient approximation (GGA). We find that the total energy of the antiferromagnetic（AFM）state is lower than the corresponding ferromagnetic (FM) state for all x studied. The GGA gives a better description of magnetic properties than LDA mainly due to its better prediction of structure, particularly for high Mn concentrations. The total spin moment of Cd1-xMnxGeP2 is～5.0µB per Mn atom. The FM alignment between Mn and Pincreases the total energy of the Mn-Mn FM coupling and makes the AFM ordering preferable.