Ferromagnetic ordering in (Ga,Mn)As related zincblende semiconductors Tomáš Jungwirth Institute of Physics ASCR František Máca, Jan Mašek, Jan Kučera Josef Kudrnovský, Alexander Shick Karel Výborný, Jan Zemen, Vít Novák, Miroslav Cukr, Kamil Olejník, et al. University of Nottingham Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, Devin Giddings et al. Hitachi Cambridge Polish Acad. of Sci. UT & Texas A&M Univ. Wuerzburg Jorg Wunderlich Tomasz Dietl Allan MacDonald Laurenc Molenkamp David Williams, et al. Mike Sawicki Jairo Sinova Charles Gould, et al. in collaboration with

Huge hysteretic low-field MR Sign & magnitude tunable by small gate valtages Spintronic transistor Current driven magnetization reversal Parkin, US Patent (2004) Magnetic race track memory Yamanouchi et al., Nature (2004) 2 orders of magnitude lower critical currents in dilute moment (Ga,Mn)As than in conventional metal FMs Sinova, Jungwirth et al., PRB (2004) Spintronics in (Ga,Mn)As dilute moment ferromagnetic semiconductor Wunderlich, et al., PRL (2006)

OUTLINE OUTLINE 1. Mn-doped GaAs material 1. Mn-doped GaAs material - only a factor of 2 short room-T otherwise outstanding properties 2. Mn-doped (Al,Ga)As and Ga(As,P) 2. Mn-doped (Al,Ga)As and Ga(As,P) - useful materials to compare with and Ga(As,P) could lead to higher T c 3. Mn-doped LiZnAs 3. Mn-doped LiZnAs - still very closely related to (Ga,Mn)As and might heal its key problems

(Ga,Mn)As material Mn As Ga 5 d-electrons with L=0  S=5/2 local moment moderately shallow acceptor (110 meV)  hole Ohno, Dietl et al. (1998,2000); Jungwirth, Sinova, Mašek, Kučera, MacDonald, Rev. Mod. Phys. (2006), - Mn local moments too dilute (near-neghbors cople AF) - Holes do not polarize in pure GaAs - Hole mediated Mn-Mn FM coupling

Universal scaling of (T c / Mn-moment) vs. (hole / Mn-moment) hole density / Mn-moment density theoryexpectations experiment Robust mean-field-like ferromagnet Jungwirth, Wang, et al. PRB (2005)

Magnetism in systems with coupled dilute moments and delocalized band electrons (Ga,Mn)As coupling strength / Fermi energy band-electron density / local-moment density

Jungwirth, Wang, et al. PRB (2005) Covalent SCs do not like doping  self-compensation by interstitial Mn Interstitial Mn Int is detrimental to magnetic order charge and moment compensation defect Yu et al., PRB ’02; Blinowski PRB ‘03; Mašek, Máca PRB '03 Mn sub Mn Int Mn sub As Ga Mn Int + - Can be annealed out T c 95K in as-grown (9% Mn) to 173 in annealed (6% Mn sub ) but Mn Ga < nominal Mn More Mn - interstitial incorporation theory & exp.

- Effective concentration of uncompensated Mn Ga moments has to increase beyond 6% of the current record T c =173K sample. A factor of 2 need (12% Mn is still a DMS). - Low solubility of group-II Mn in III-V-host GaAs makes growth difficult Low-temperature MBE More Mn - problem with solubility

A startegy: Find DMS system as closely related to (Ga,Mn)As as possible to with larger hole-Mn spin-spin interaction lower tendency to self-compensation by Mn int larger Mn solubility independent control of local-moment and carrier doping (p- & n-type)

conc. of wide gap component 0 1 lattice constant (A) (Al,Ga)As Ga(As,P) (Al,Ga)As & Ga(As,P) hosts d5d5 d5d5 local moment - hole spin-spin coupling J pd S. s Mn d - As(P) p overlapMn d level - valence band splitting GaAs & (Al,Ga)As (Al,Ga)As & Ga(As,P)GaAs Ga(As,P) Mn As Ga

Smaller lattice const. more important for enhancing p-d coupling than larger gap  Mixing P in GaAs more favorable for increasing mean-field T c than Al Up to a factor of ~1.5 T c enhancement p-d coupling and T c in mixed (Al,Ga)As and Ga(As,P) Mašek, et al. preprint (2006) Microscopic TBA/CPA or LDA+U/CPA (Al,Ga)As Ga(As,P) 10% Mn 5% Mn theory

No reduction of Mn int in (Al,Ga)As Mixing P in GaAs more favorable for suppressing Mn int formation Mn int formation in mixed (Al,Ga)As and Ga(As,P) higher in (Al,Ga)As and Ga(As,P) than in GaAs smaller interstitial space only in Ga(As,P) theory

d4d4 d Weak hybrid. Delocalized holes long-range coupl. Strong hybrid. Impurity-band holes short-range coupl. d 5  d 4 no holes InSb, InAs, GaAsT c : 7  173 K (GaN ?) GaP T c : 65 K Similar hole localization tendencies in (Al,Ga)As and Ga(As,P) Scarpulla, et al. PRL (2005) d5d5 Limits to carrier-mediated ferromagnetism in (Mn,III)V

III = I + II  Ga = Li + Zn GaAs and LiZnAs are twin SC Wei, Zunger '86; Bacewicz, Ciszek '88; Kuriyama, et al. '87,'94; Wood, Strohmayer '05 Masek, et al. preprint (2006) LDA+U sais that Mn-doped are also twin DMSs

Additional interstitial Li in Ga tetrahedral position - donors n-type Li(Zn,Mn)As No solubility limit for group-II Mn substituting for group-II Zn theory

L As p-orb. Ga s-orb. As p-orb. EFEF Comparable T c 's at comparable Mn and carrier doping and Li(Mn,Zn)As lifts all the limitations of Mn solubility, correlated local-moment and carrier densities, and p-type only in (Ga,Mn)As Electron mediated Mn-Mn coupling n-type Li(Zn,Mn)As - similar to hole mediated coupling in p-type (Ga,Mn)As

Conclusions Conclusions 1. Relatevily small technological investment in Mn-doped (Al,Ga)As 1. Relatevily small technological investment in Mn-doped (Al,Ga)As - useful info about trends in III-V's and for Ga(As,P) 2. More tech. difficult Mn-doped Ga(As,P) 2. More tech. difficult Mn-doped Ga(As,P) - could lead to higher T c 3. Adventureous Mn-doped LiZnAs 3. Adventureous Mn-doped LiZnAs - might heal key problems in (Ga,Mn)As & n-type FS

T c linear in Mn Ga local moment concentration Falls rapidly with decreasing hole density in more than 50% compensated samples Nearly independent of hole density for compensation < 50%. Intrinsic properties of Ga 1-x Mn x As As Ga Mn super-exchange (anti-ferro) kinetic exchange (RKKY) hole density (nm -3 )hole density / Mn density room-T c for x=10% Effective kinetic-exchange Hamiltonian, microscopic TBA or LDA+U

Extrinsic effects - covalent SC do not like doping  self-compensation by interstitial Mn Interstitial Mn I is detrimental to magnetic order:  compensating double-donor – reduces carrier density  attracted to substitutional Mn Ga acceptor and couples antiferromagnetically to Mn Ga even at low compensation Yu et al., PRB ’02; Blinowski PRB ‘03; Mašek, Máca PRB '03 Mn Ga As Ga Mn I + -

T c in as-grown and annealed samples Tc=173K 8% Mn Open symbols as-grown. Closed symbols annealed Total Mn doping (%)

Mn Ga As Ga Mn I + - Linear increase of T c with effective Mn moment doping T c increases with Mn eff when compensation is less than ~40%. No saturation of T c at high Mn concentrations Closed symbols are annealed samples High compensation Mn eff = Mn Ga -Mn I Effective Mn doping (%)

(III,Mn)V materials: Microscopic picture of Mn-hole coupling in (Ga,Mn)As L Mn Ga AsAs Ga s-orb. As p-orb. 1 Mn 0.1eV acceptor many Mn d5 d5  d5 d5  As 4p - Mn 3d hybridization   GaAs Mn

Mn d  level Mn d  level EdEd EdEd |V pd | 2 ~ a lc -7 Hole - local moment Kondo coupling: Mixed (Al,Ga)As and Ga(As,P) hosts 1/|E d  | + 1/|E d  | ~ const. = Mean-field Curie temperature: 4% in GaP and AlAs 50% in GaP