Current Nanospin related theory topics in Prague in collaboration with Texas and Warsaw based primarily on Nottingham and Hitachi experimental activities

Range of materials or model systems -2D models with simple Rashba spin-orbit coupled bands -Dilute-moment ferromagnetic semiconductors: still simple bands yet strongly exchange and SO split dilute moment – tunable, weak dipolar fields, smaller STT currentsAsGa Mn -Systems with complex bands but room T c : FeNi, CoFe, CoPt,….

Technical issues -Analytical calculations (Rashba model) k.p semiphenomenological modelling (typical for semiconductors) extensive library of home-made routines spd-tight-binding modelling (half way between phenomenological and ab initio) home-made codes Full ab initio heavy numerics (transition metals based structures) standard full-potential libraries, home-made relativistic ab-initio codes -Conclusions derived from bulk band structures total energy calculations, Boltzmann and Kubo transport equations Device specific modeling Landauer-Buttiker formalism

Extraordinary magnetoresistance (AHE/SHE, AMR, STT) B V I _ _ _ _ _ _ FLFL Ordinary magnetoresistance: response in normal metals to external magnetic field via classical Lorentz force Extraordinary magnetoresistance: response to internal magnetization in ferromagnets via quantum-relativistic spin-orbit coupling e.g. ordinary (quantum) Hall effect I _ F SO _ _ _ majority minority V e.g. anomalous Hall effect or anisotropic magnetoresistance

Intrinsic vs. extrinsic AHE in Rashba 2D systems semicalssical Boltzmann eq. intrinsic skew scatteringside jump group velocity distribution function quantum Kubo formula int.skew side jump sc. Solvable analytically

Proposed experimental setup skew scattering term: - absent in 2DEG for two-band occupation - absent in 2DHG for any band occupation extenting the study to: - 4-band spherical Kohn-Luttinger model - full 6(multi)-band model of DMSs - ab initio band structures of metals Rashba spherical K-L model so far microscopic calculations of intrinsic AHE only in these systems

Origin of non-crystalline and crystalline AMR in GaMnAs ~(k. s) 2 ~M x. s x SO-coupling – spherical model FM exchange spiitting hot spots for scattering of states moving  M  R(M  I)> R(M || I) Boltzmann eq. in relax. time approximation1 st order Born approximation 4-band spherical Kohn-Luttinger model kyky kxkx kxkx kxkx kyky kyky M M 1/  k (M)

M [110] current ) )   theory exp. spherical model: non-crystalline AMR only full 6-band Hamiltonian: non-crystalline and crystalline AMR - explains sign of non-crystalline AMR - consistent with experimentally seen increasing role of crystalline terms with increasing compensation - large AMR dominated by crystalline terms in ultrathin layers not explained by bulk theory M current ) 

Mn Ga As Mn Ferromagnetism mediated by As p-orbital-like band states: - basic SO coupling related symmetries similar to familiar GaAs, unchanged by Mn Ga - carriers with strong SO coupling and exchange splitting due to hybridization with Mn Ga d-orbitals pxpx pypy - straightforward means for relating intuitive physical pictures with microscopic calculations - compare with ferro metals: model of scattering of non-SO-coupled non-exchange-split s-state carriers to localized d-states  difficult to match with ab initio theories with mixed s-d carriers

Strain and doping-depent magnetocrystalline anisotropy macroscopic elastic theory simulations of strains GaMnAs microscopic magneto- crystalline anisotropies

New device functionalities and new opportunity for exploring the rich phenomenology of magnetocrystalline anisotropies in (Ga,Mn)As

Close relatives to GaMnAs with new degrees of freedom n-type DMSs, higher T c,… III = I + II  Ga = Li + Zn GaAs and LiZnAs are twin semiconductors Prediction that Mn-doped are also twin ferromagnetic semiconductors No limit for Mn-Zn (II-II) substitution Independent carrier doping by Li-Zn stoichiometry adjustment Limited confidence in ab initio calc. Reasonable confidence when comparing to GaMnAs bench-mark material

L As p-orb. Ga s-orb. As p-orb. EFEF Electron mediated Mn-Mn coupling in n-type Li(Zn,Mn)As similar to hole mediated coupling in p-type (Ga,Mn)As Tc~Tc~

Family of I-II-V hosts

- theoretical exploration of I-II-V’s  I-Mn-V’s  I-(II,Mn)V DMSs - MOCVD growth of the most promising theory candidates - MBE growth to achieve better stoichiometry control for the promising MOCVD materials

Mn I 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) Less interstitials in Ga(As,P) more interstitials in (Al,Ga)As

L As p-orb. Ga s-orb. As p-orb. EFEF n-type AlAs with int. Mn only Comparable T c to n-type hosts with substitutional Mn moments electrons can mediate FM coupling for both subst. and int. Mn