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Diluted Magnetic Semiconductors

Diluted Magnetic Semiconductors. Diluted Magnetic Semoconductor (DMS) A ferromagnetic material that can be made by doping of impurities, especially transition metal elements, into a semiconductor host.

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Diluted Magnetic Semiconductors

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  1. Diluted Magnetic Semiconductors • Diluted Magnetic Semoconductor (DMS) • A ferromagnetic material that can be made by doping of impurities, especially transition metal elements, into a semiconductor host. • Conducting spin polarized carriers of DMS exhibit similar characters those of host semiconductors. • Compatible with current semiconductor industry.

  2. TM TM Role of TM Impurities in DMS Material • Local Magnetic Moment

  3. Role of TM Impurities in DMS Material • Splitting Valence Band Spin Polarized Carrier Finally Used for Spin Manipulation

  4. TM TM Which Impurity is Possible for DMS? Local Moments and Splitting Valence Bands Simultaneously

  5. Success and Failure of Ga1-xMnxAs • Mn substitutes Ga in zincblende structure • Structure is compatible with GaAs 2DEG • Tc is correlated with carrier density • Ferromagnetic semiconductor with ordering temperature ~ 160 K Mn Ku et al., APL 82 2302 (2003)

  6. Density of States of GaMnAs Total DOS and Mn d state*10 As state Delocalized Carrier due to p-d Exchange Interaction Localized Moment due to Mn

  7. Comparison of GaMnAs and GaMnN GaN:Mn GaAs:Mn • Total magnetic moment: 4 μB • Mn local moment of Mn < 4 μB • d4 configuration • Fermi level on the narrow impurity band • No spin split of valence band • Not strong p-d hybridization. • Very strong d character of holes • Much higher value of exchange constant • Double exchange mechanism • Total magnetic moment: 4 μB • Mn local moment of Mn > 4 μB • d5+h configuration • Fermi level under VBM • Spin split of valence band • Strong p-d hybridization • Strong d character of holes • -4.5 eV of exchange constant • Hole mediated mechanism

  8. Structure of 64-Atom GaN Transition Metal 5th Nitrogen 1st NN Nitrogen 4th Nitrogen 3rd NN Nitrogen 2nd NN Nitrogen

  9. Methods • Planewave Pseudopotential Method: VASP.4.6.21 • XC functional: GGA(PW91) • Cutoff energy of Planewave: 800 eV • 4X4X4 k point mesh with MP • Electronic Relaxation: Davidson followed by RMM-DIIS • Structure Relaxation: Conjugate Gradient • Force Convergence Criterion: 0.01 eV/A • Gaussian Smearing with 0.1 eV for lm-DOS • Treatment of Ga 3d state • Semicore treatment for GaN • Core treatment for GaAs

  10. Total and Local Magnetic Moments Less-Than Half filled More-than Half filled Magnetic moments of V, Cr, and Mn doped systems are concentrated on TM ion itself. On the contrary, magnetic moments of Fe, Co, Ni, and Cu are rather long-ranged. Localization of magnetic moments on the TM ion is not appropriate for successful DMS materials since delocalized spin polarized carrier is important for spin manipulation

  11. Induced Magentic Moments of Nitrogen For V, Cr, and Mn induced magnetic moments of N with the distance from the TM ion are much smaller than those of Fe, Co, Ni, and Cu. This also suggest that the V, Cr, Mn are not a candidate for DMS application. Materials having long-ranged interaction such as Fe, Co, Ni, and Cu passed the first test for DMS application.

  12. Partial DOSs having More-Than Half Filled States GaCoN: Half Metal GaFeN: Magnetic Insulator GaCuN: Half Metal GaNiN: Magnetic Insulator

  13. Electron Occupation in GaN No Splitting of Valence p-band GaN:Co(9)-half metal GaN:Mn(7)-half metal Up Spin Up Spin Up Spin Down Spin Up Spin Up Spin Up Spin Down Spin t2g eg GaN:Ni(10)-insulator GaN:Cu(11)-half metal Up Spin Up Spin Up Spin Down Spin Up Spin Up Spin Up Spin Down Spin Filled Electron Unfilled Electron

  14. Interaction Range of Transition Metals in GaN V, Cr, Mn From the viewpoint of valence band splitting and half metallicity, Co and Cu doped GaN are most probable candidates Fe, Co, Ni, Cu

  15. Hamiltonian based on p-d Hybridization p-d hybridization results in a spin dependent coupling between the holes and the Mn ions. Cu showed larger value of N0ß that Co system  Cu doped system might be higher Curie temperature

  16. Formation Energy of GaN:TM Transition Metal Ga GaN GaN:TM Reactant Product

  17. Formation Energy of GaN:TM Since the formation energy for Cu is larger than other transition elements, the control of doping level might be difficult.

  18. Co, Cu Co, Cu Summary Cu doped GaN is predicted to be the most probable candidate for DMS application among 3d transition elements because the system induces long range splitting of valence band and higher p-d hybridization.

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