Daresbury Laboratory Ferromagnetism of Transition Metal doped TiN S.C. Lee 1,2, K.R. Lee 1, K.H. Lee 1, Z. Szotek 2, W. Temmerman 2 1 Future Technology Research Division, Korea Institute of Sci. Tech. 2 Band Theory Group, Daresbury Laboratory 20 September 2005 Ψ k 2005, Schwäbisch Gmünd

Daresbury Laboratory Spintronics D. Awschalom et al, Scientific American (2002) Magnetic Tunneling JunctionSpin Field Effect Transistor Spin dependent tunneling Magnetic RAM Semiconductor based device Next generation of spintronics Control of Spin and Charge of Electrons Simultaneously

Daresbury Laboratory G. Schmidt et al., PRB (2000) Spin Injection from FM Metal to SC FM Metal PM SC Spin Injection

Daresbury Laboratory Proposed Solutions Novel Materials - Diluted magnetic semiconductors (DMSs) : σ sc /σ fm ~ 1 Fielderling et al., Nature (1999); Ohno et al. Nature (1999) - Half metallic ferromagnets : β ~ 1 - Or, something else? Interface Manipulation - Tunneling barrier at the FM/SC interaction - Intrinsic Schottky barrier - Spin-dependent interface resistance

Daresbury Laboratory 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

Daresbury Laboratory Crystal structure: Rocksalt structure Average resistivity: 100~1000  cm  Semi-metal Well known for a diffusion barrier in semiconductor industries Conducting Nitride: TiN

Daresbury Laboratory Charateristics of TiN (1) Resistivity of TiN is compatible to that of SCs  100 ~ 1000  cm  Highly doped SC: ~ 1000  cm pd-hybridized electrons contribute to electric conduction Ti d-state N p-state Total DOS

Daresbury Laboratory Characteristics of TiN (2) TiN can make a sharp interface with semiconductor TiN/SC interface can form an Ohmic contact TiN is widely used in SC industries as a diffusion barrier Ruterana et al. MRS Symp. Proc. F99W11.75 (1999)

Daresbury Laboratory Self Interaction Correction-Local Spin Density SIC-LSD The LSDA and GGA are not exact for one electron systems - Self interaction energy is not zero in LSD - Self interaction Correction (Perdew and Zunger, 1981) Orbital dependent potential differentiates between localized and delocalized electrons Gain in band formation vs. gain in localization (SIC energy) Study of various localization/delocalization configurations Global energy minimum determines ground state configuration

Daresbury Laboratory Calculation Details SIC-LSD implemented in TB-LMTO method Self interaction correction for transition metals 16 atoms supercell with rocksalt structure TM substitutes Ti site. ASA radii: TM and Ti =2.62 a.u., N=2.34 a.u. Partial waves: -TM & Ti: 4s, 4p and 3d as low waves - N: 2s, 2p as low waves and 3d as intermediate wave 124 atoms screening clusters Transition metals: V, Cr, Mn, Fe, Co, Ni and Cu

Daresbury Laboratory Electron Configuration & Ionicity of Ti 7 TM 1 N 8 ElementsUp SpinDown SpinIonicity V --PM Cr ↑ ↑ ↑ (t 2g )-+3 Mn ↑ ↑ ↑ ↑ ↑-+2 Fe ↑ ↑ ↑ ↑ ↑-+3 Co ↑ ↑ ↑ ↑ ↑↓ (1 t 2g )+3 Ni ↑ ↑ ↑ ↑ ↑↓ ↓ ↓ (t 2g )+2 Cu ↑ ↑ ↑ ↑ ↑↓ ↓ ↓ ↓(t 2g +1 e g )+2 N valence =Z-N core - N SIC(LOC)

Daresbury Laboratory Total Magnetic Moments Magnetic Moments of TM doped TiN CrMn CoFe NiCu Local Magnetic Moments

Daresbury Laboratory Spin Polarization at E F Spin Polarization of TM doped TiN

Daresbury Laboratory CrMn CoFe NiCu TM doped TiN: DOS

Daresbury Laboratory Conclusion TM Doped TiN PM SC Transition metal doped TiNs show local magnetic moments. Among various transition metals, Cu doped TiN seems to be a promising candidate for spin injector. Other materials specific properties such as N vacancies and larger unit cells should be studied. TiN Ga N