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.

Local Magnetic Moment Role of TM Impurities in DMS Material TM

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

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

Success and Failure of Ga 1-x Mn x As Mn substitutes Ga in zincblende structure –Structure is compatible with GaAs 2DEG T c is correlated with carrier density Ferromagnetic semiconductor with ordering temperature ~ 160 K Ku et al., APL (2003) Mn

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

Comparison of GaMnAs and GaMnN Total magnetic moment: 4 μ B Mn local moment of Mn > 4 μ B d 5 +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 GaAs:Mn Total magnetic moment: 4 μ B Mn local moment of Mn < 4 μ B d 4 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 GaN:Mn

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

 Planewave Pseudopotential Method: VASP  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 Methods

More-than Half filled Total and Local Magnetic Moments Less-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

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.

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

Up SpinDown SpinUp Spin t 2g egeg Filled ElectronUnfilled Electron Up SpinDown SpinUp Spin GaN:Mn(7)-half metal GaN:Co(9)-half metal Up SpinDown SpinUp Spin GaN:Ni(10)-insulator Up SpinDown SpinUp Spin GaN:Cu(11)-half metal Electron Occupation in GaN No Splitting of Valence p-band

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

Hamiltonian based on p-d Hybridization p-d hybridization results in a spin dependent coupling between the holes and the Mn ions. TM in GaNΔE valenc e (eV)N o β (eV) Local Moment(μ B ) Fe Co Ni Cu GaAs:Mn Cu showed larger value of N 0 ß that Co system  Cu doped system might be higher Curie temperature

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

Formation Energy of GaN:TM Element Total E GaN:TM Total E Pure TM Delta E (B-C) Difference in Formation E (eV) Fe Ni Cu Since the formation energy for Cu is larger than other transition elements, the control of doping level might be difficult.

Summary Co, Cu 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.