1. Spintronics at Univ. L’Aquila Firstprinciples calculations: FLAPW, PWSCF, DMol 3 A. Continenza, S. Picozzi Northwestern Univ., USA (Y.J.Zhao, A.J.Freeman, T.Shishido ) Univ. Trieste (M. Peressi, A.De Bernardi )

2. Spintronics at Univ. L’Aquila Univ. Catania (F. Priolo et al. ) Experiments (growth + cha- racterization) Univ.Camerino (N.Pinto, F. Gunnella, M. De Crescenzi) F. D’Orazio, F. Lucari, M. Passacantando, P. Picozzi

3. Materials explored Heusler Alloys (Co 2 MnSi, Co 2 MnGe, Co 2 MnSn) Mn-doped II-IV-V 2 Mn: CdGeP 2 (i.e. Mn: CdGeP 2 ) Mn-doped I-III-VI 2 (i.e. Mn: CuGaS 2 Mn: CuGaS 2 ) Heusler/semiconductorInterfaces (I.e. Co 2 MnGe/GaAs, Co 2 MnGe/Ge) Mn-doped Si, Ge, SiGe alloys Mn, Cr and V-dopedBeTe

4. Spin injection at Co 2 MnGe/semiconductor interfaces: ab-initio study Focus on Half-metallicity of heusler compound: Effect of defects Effect of junction S. Picozzi et al. JAP 94, 4723 (2003); PRB 66,094421 (2002) ? ?

5. Co-antisite Co-Mn swap Mn-antisite 38.000.33Mn antisite 36.001.17Co-Mn swap 38.370.84Co antisite M tot (  B ) H f (eV)  Quite low formation Energies  Half-metallicity is kept (lost) with Mn (Co) antisites Ge Mn Co Defect effects

6. Interface effects perturbationsinterface  Strong perturbations induced by the interface Interface gap statesboth  Interface gap states present at both sides sides of the interface  Interface gap states  Interface gap states in the Heusler Heusler side: half-metallicity is locally lost ! locally lost !  States decay away from interface (3 to 5 layers): interface (3 to 5 layers): D(E F ) vs z at D(E F ) vs z at Co 2 MnGe GaAs [001]

7. Schottky barrier height: effect of the semiconductor 0.08 eV 0.5 eV <  B < 0.7 eV  B = E F - VBM semic “Ohmic”“Tunnel”Spin-injection process Almost ohmic for holes (E F close to VBM) Schottky (E F pinned in the gap) Type of contact GeGaAs Co2MnGe/GaAs Co2MnGe/Ge

8. Mn-doping in Ge and Si Mn Ge Spin density localized on Mn sites Induced negative mom. on nearest neighbor with evident p- character: AFM Mn- Ge coupling re- lated to Zener FM? Oscillatory trend for induced moment as a function of distance from Mn impurity

9. Trends with Mn concentration in Si, Ge: relevant properties  FA : Difference between FM and AFM total energy: FM favored Similar behavior for Si and Ge  FA Increases with Mn conc x: Consistent with expts Magnetic moments: MnGe keeps integer moment (equal to 3  B ) for all x MnSi show variations with x: larger p-d hybridization for Si Magnetism essentially of 3d origin

10. “Real atoms” Absolute magnetic moments Total magnetic moments Formation energies Virtual crystal Mn-doping in Si x Ge (1-x) cells (3.13% Mn)

11. Mn/Digital alloys The Mn-doped layers produce a potential well The depth of the potential well is affected by the Mn concentration: upon doubling of the concentration, the barrier doubles A potential barrier is also present for carriers in the Ge- region (not dependent on spin). Mn_ML 1 Ge spacer 3 Ge spacers Mn-doped planes

12. Carrier properties Charge on Ge Spin. Dens. on Ge

13. What can we do? First principles calculations of: Structural properties heats of formation phase stability defects energetics Electronic and magnetic properties magnetization magnetic alignment Carrier properties Carrier confinment, spin-polarization Magneto-optics related quantities (MOKE, XMCD) Conductivity tensor STM and Spin-Pol. STM maps