Summary and prospects in the field of magnetically doped semiconductors Tomasz Dietl Laboratory for Cryogenic and Spintronic Research, Institute of Physics, Polish Academy of Sciences Institute of Theoretical Physics, University of Warsaw, Poland WPI-AIMR Tohoku University, Sendai, Japan FunDMS see, A. Bonanni and T. Dietl, Chem. Soc. Rev. 39, 528 (2010) T. Dietl and H. Ohno, Rev. Mod. Phys. 86, 187 (2014)

Summary and prospects in the field of magnetically doped semiconductors Tomasz Dietl Laboratory for Cryogenic and Spintronic Research, Institute of Physics, Polish Academy of Sciences Institute of Theoretical Physics, University of Warsaw, Poland WPI-AIMR Tohoku University, Sendai, Japan FunDMS see, A. Bonanni and T. Dietl, Chem. Soc. Rev. 39, 528 (2010) T. Dietl and H. Ohno, Rev. Mod. Phys. 86, 187 (2014) Unanticipated richness of materials science challenges Test beds for spintronic functionalities

Magnetically doped semiconductors Accomplishments

Magnetically doped semiconductors Accomplishments Prospects, challenges, emerging fields, …

Magnetically doped semiconductors Accomplishments Prospects, challenges, emerging fields, … Role of nuclear methods (other talks, discussion, ) characterization, fabrication, …

Moessbauer isotopes

Moessbauer isotopes and more …. channeling

Outline Mamagnetically doped semiconductors summary, prospects, challenges, emerging fields, …

Outline Mamagnetically doped semiconductors summary, prospects, challenges, emerging fields, … dopants semiconductors magnetic interactions magnetic ground states functionalities

Outline Mamagnetically doped semiconductors summary, prospects, challenges, emerging fields, … dopants semiconductors magnetic interactions magnetic ground states functionalities The case study – magnetically-doped nitrides  Alberta Bonanni

Dilute magnetic semiconductors (DMSs) III-V II-VI Al P Cr Zn S Cr Ga As Mn Cd Se Mn In Sb Fe Hg Te Fe Galazka ‘77

Magnetic elements

Magnetic dopants Transition metals: open 3d shell but also 4d e.g. Ru Rare earth: 4f but also actinides: 5f, e.g. U Magnetically active defects and impurities d0 ferromagnetism p ferromagnetism Contamination

Magnetic dopants Transition metals: open 3d shell but also 4d e.g. Ru Rare earth: 4f but also actinides: 5f, e.g. U Magnetically active defects and impurities d0 ferromagnetism p ferromagnetism Contamination doping methods: also ion implantation, isotope transmutation, …

Single impurity limit

TM, RE doping – single impurity limit Questions answers depend on growth method/co-doping incorporation into the lattice – not always cation substitution energy levels electrical activity charge and spin state Jahn-Teller distortion hybridization with band states defect generation formation of complexes with defects/impurities …. T.D. (SST’2002)

Interstitial position e.g. part of Mn in MBE-(Ga,Mn)As) Mn interstitials: -- donors  compensate holes -- form AF pairs with MnGa  compensate spins K. M. Yu et al. (Berkeley, Notre-Dame, PRB’2012)

Antisite position e.g. part of Mn in Mn-implanted (Ga,Mn)N - channeling L.M.C. Pereira et al. (Leuven, Lisboa) PRB'12

Complexes e.g. Mn-Mgk complexes in (Ga,Mn)N:Mg T. Devillers et al. (Linz, Warsaw), Sci. Reports 2012

Contamination e.g. etched Si 300 K 300 K P. J. Grace et al. (TCD, Weizmann) Adv. Mat.’09

Contamination e.g. etched Si 300 K 300 K P. J. Grace et al. (TCD, Weizmann) Adv. Mat.’09

Contamination e.g. etched Si  Fe from glass 300 K 300 K P. J. Grace et al. (TCD, Weizmann) Adv. Mat.’09  Fe from glass Fe-containing nanoparticles main source of ferro contamination

Many impurities - DMS

Distribution of magnetic dopants Key insight d orbitals contribute to bonding  attractive force between TM cations (chemical interactions)  non-random distribution of TM ions at thermal equilibrium Exceptions (true DMSs) -- (II,Mn)VI -- growth far from thermal equilibrium, e.g., LT-MBE of (Ga,Mn)As Types of non-random distribution -- crystallographic phase separation (precipitation) -- chemical phase separation (spinodal decomposition)  locally high density of TM  condensed magnetic semiconductors (CMS)

Nanocrystals e.g., annealed (Ga,Mn)As Hexagonal MnAs nanocrystals in GaAs Cubic (Mn,Ga)As nanocrystals in GaAs M. Moreno et al. (Berlin) JAP’02

Nanocolumns wz-(Al,Cr)N zb-(Zn,Cr)Te (Ge,Mn) TEM/EDS TEM/EELS 25nm N. Yotaro, et al. (Tsukuba, Warsaw) MRS Proc.’09 L. Gu et al. (Arizona) JMMM’06 (Ge,Mn) TEM/EELS M. Jamet et al. (Grenoble) Nature Mat. ’06 cf. D. Bougear et al.. (WSI Garching)

Controlling TM distribution TM distribution depends more on growth/processing than on TM/host combination Aggregation can be enhanced by -- high growth temperature -- slow growth rate Can be affected by changing valence of TM ions -- co-doping -- electrical/optical carrier injection during growth

Effect of doping on spinodal decomposition TM charge state is controlled by co-doping with shallow impurities. Because of Coulomb repulsion spinodal decomposition is blocked if TM is charged Cr+2 EF ZnTe Cr+3 ZnTe:N T.D., Nature Mat.’06 L.-H. Ye et al. (NWU) PRB’06

Effect of co-doping on magnetism [I] ~ 2 x 1018 cm-3 Cr2+ Te-rich growth Cr2+/Cr3+ [N] ~ 3 x1020 cm-3 Cr3+ S. Kuroda … T.D. (Tsukuba, Warsaw) Nature Mat., ’07

Effect of co-doping on Cr distribution I-doped 50nm Optimized TEM/EDS Inhomogeneous S. Kuroda ... T.D. (Tsukuba, Warsaw) Nature Mat., ’07

Effect of co-doping on Cr distribution I-doped N-doped 50nm Optimized N-doped TEM/EDS Inhomogeneous Homogeneous S. Kuroda … T.D. (Tsukuba, Warsaw) Nature Mat., ’07

Magnetic interactions between localized spins Dominant interaction in non-metals -- superexchange TM cation TM cation anion Always present: usually antiferromagnetic, e.g. Mn2+ [reduces M(T,H)] DMS – random antiferromagnets spin-glass freezing at low T

Zn1-xCoxO – inverse magnetic susceptibility grown by ALD at 160oC x = 42% M. Sawicki et al. [Warsaw] PRB’2013 antiferromagnetic superexchange

Zn1-xCoxO – spin-glass freezing M. Sawicki et al. [Warsaw] PRB’2013

Effects of TM spins on band states sp-d exchange interaction in DMSs H = - Isp-dsS -- spin disorder scattering -- formation of magnetic polarons -- giant spin splitting of bands proportional to magnetization of localized spins

Giant splitting of exciton states ~ M(T,H) E ~ M ~ BS(H) c.b. v.b. geff > 102 J. Gaj et al., R. Planel,.. A. Twardowski et al. G. Bastard, … -- p-d: Ipd  No  - 1.0 eV large p-d hybridization and large intra-site Hubbard U => kinetic p-d exchange -- s-d: Isd  No  0.2 eV no s-d hybridization => potential s-d exchange

Ferromagnetic superexchange TM cation TM cation anion usually antiferromagnetic, e.g. Mn2+ [reduces M(T,H)] sometimes ferromagnetic [enhances M(T,H)] eg. (Ga,Mn)N with Mn3+, TC up to 12 K  ferromagnetic Mott-Hubbard insulator cf. Alberta Bonanni

RKKY and Bloembergen-Rowland mechanism spin polarisation of carriers spin polarisation of valence electrons  Dominates in topological insulators 4th order process in hybridisation <k|H |d>

Zener/RKKY model of ferromagnetism Competition between entropy, AF interactions, and lowering of carrier enrgy owing to spin-splitting Curie temperature TC = TCW = TF – TAF superexchange TF = S(S+1)xeffNo(s)(EF)I2/12 (s)(EF) ~ m*kFd-2 (if no spin-orbit coupling, parabolic band) => TC ~ 50 times greater for the holes large m* large Ip-d T.D. et al. PRB’97,’01,‘02, Science ’00

Making DMS ferromagnetic – p-type doping holes mediate ferro coupling in DMS source of holes in Mn-based DMSs, x < 10%: Mn itself III-V (In,Mn)As; (Ga,Mn)As H. Ohno et al. [IBM, Tohoku] PRL’92, APL’96 (Sb,Mn)2Te3; (Bi,Mn)2Te3 Choi et al. [Ulsan] pps(b)’04 TC up to 190 K TC up to 20 K

Making DMS ferromagnetic – p-type doping valence band holes mediate ferro coupling in p-type DMS source of holes in Mn-based DMSs, x < 10%: Mn itself III-V (In,Mn)As; (Ga,Mn)As H. Ohno et al. [IBM, Tohoku] PRL’92, APL’96 (Sb,Mn)2Te3; (Bi,Mn)2Te3 Choi et al. [Ulsan] pps(b)’04 acceptor impurities (Cd,Mn)Te:N, (Zn,Mn)Te:P TD, Cibert et al. [Grenoble, Warsaw] PRB’97, PRL’97, PRL’03 (K,Ba)(Zn,Mn)2As2 et al. [Beijing, Columbia U.] Nat. Commun.’13 TC up to 190 K TC up to 20 K TC up to 5 K TC up to 180 K

Making DMS ferromagnetic – p-type doping valence band holes mediate ferro coupling in p-type DMS source of holes in Mn-based DMSs, x < 10%: Mn itself III-V (In,Mn)As; (Ga,Mn)As H. Ohno et al. [IBM, Tohoku] PRL’92, APL’96 (Sb,Mn)2Te3; (Bi,Mn)2Te3 Choi et al. [Ulsan] pps(b)’04 acceptor impurities (Cd,Mn)Te:N, (Zn,Mn)Te:P TD, Cibert et al. [Grenoble, Warsaw] PRB’97, PRL’97, PRL’03 (K,Ba)(Zn,Mn)2As2 et al. [Beijing, Columbia U.] Nat. Commun.’13 cation vacancies IV-VI, [I-II]-V (Pb,Sn,Mn)Te T. Story et al. [Warsaw] PRL’86 (Ge,Mn)Te Y. Fukuma et al. [Yamaguchi] APL’08 [Li(Zn,Mn)]As Z. Deng et al. [Beijing, Columbia,Tokyo, Vancouver] Nature Comm.’11 TC up to 190 K TC up to 20 K TC up to 5 K TC up to 50 K TC up to 10 K TC up to 180 K

TC in p-type (III,Mn)V p-d Zener model/expl. T.D. et al., Science’00 InSb: T. Jungwirth et al., PRB’02 Berkeley Prague/Nottingham/Beijing Kanagawa Tohoku Notre Dame

High TC ferromagnetic semiconductors

wz-c-(Ga,Mn)N, (Ga,Fe)N, (In,Mn)N, (Al,Mn)N, (Ga,Cr)N, (Al,Cr)N DMS, DMO, and non-magnetic materials showing spontaneous magnetization at 300 K wz-c-(Ga,Mn)N, (Ga,Fe)N, (In,Mn)N, (Al,Mn)N, (Ga,Cr)N, (Al,Cr)N (Ga,Mn)As, (In,Mn)As, (Ga,Mn)Sb, (Ga,Mn)P:C (Zn,Mn)O, (Zn,Ni)O, (Zn,Co)O, (Zn,V)O, (Zn,Fe,Cu)O, (Zn,Cu)O (Zn,Cr)Te (Ti,Co)O2, (Ti,V)O2, (Ti,Cr)O2, (Sn,Co)O2, (Sn,Fe)O2, (Hf,Co)O2 (Cd,Ge,Mn)P2, (Zn,Ge,Mn)P2, (Cd,Ge,Mn)As2, (Zn,Sn,Mn)As2 (Ge,Mn), (Ge,Cr), (Ge,Mn,Fe), (Si,Fe), (Si,Mn), (SiC,Fe) (La,Ca)B6, CaB2C2, C, C60, HfO2, ZnO, GaN:Gd, GaN:Eu... holes unnecessary TM ions unnecessary confirmed by ab initio works in many cases properties strongly dependent on the growth conditions

Functionalities

Magnetically-doped semiconductors - functionalities Localized gap states cf. Hannes Raebiger – ab initio -- carrier trapping (TM gap levels, Zhang-Rice polarons)  semi-insulating substrates GaAs:Cr, InP:Fe, GaN:Fe, …

Magnetically-doped semiconductors - functionalities Localized gap states -- carrier trapping (TM gap levels, Zhang-Rice polarons)  semi-insulating substrates GaAs:Cr, InP:Fe, GaN:Fe, … -- intra-center optical transitions  LEDs ZnSe:Mn  broad band optically pumped lasers oxides: TM, ZnSe:Cr, ... S. Mirov et al.. Laser & Photon. Rev. 4, No. 1, 21–41 (2010) Challenge: electrically pumped broadband lasers

Optical insulators of DMS absorption (+) > (-)  magnetic circular dichroism  large Faraday rotation optical isolators: J. Gaj, M. Nawrocki, R. Gałązka SSC’78 laser (Cd,Mn)Te magnet fiber F = /4 spintronic device Challenge: optical isolators of ferromagnetic semiconductors

Functionalities of ferromagnetic insulators Spin filtering tunneling barriers Spin current leads via magnons Split topological surface and edge states ….

Functionalities of hole-mediated ferromagnets Controlling magnetization direction by an electric field low-power magnetization switching Chiba et al. [Tohoku, Warsaw] Nature’08

Functionalities of hole-mediated ferromagnets Controlling magnetization direction by an electric field physics: repopulation of v.b. subbands affects holes’ L and via s.o. s low-power magnetization switching D. Chiba et al. [Tohoku, Warsaw] Nature’09

Uniaxial in-plane magnetic anisotropy – p-d Zener modeling J. Zemen et al. [Prague] PRB'09, Birowska et al. [Warsaw] PRL’12 W. Stefanowicz et al. [Warsaw, Regensburg] PRB‘10

Summary Three families of ferromagnetic DMSs -- high temperature ferro DMSs, DMOs, TC up to 900 K -- dilute ferromagnetic insulators, TC up to 15 K superexchange -- carrier-mediated ferromagnetic DMSs, TC up to 190 K p-d Zener model

Outlook Unanticipated richness of materials science challenges Test beds for spintronic functionalities

Outlook Unanticipated richness of materials science challenges Test beds for spintronic functionalities Challenge: understanding and functionalizing high TC in semiconductors aggregation of TM ions? d0 ferromagnetism? contamination? ….

Outlook Challenge: how to go to 300 K with proven functionalities Unanticipated richness of materials science challenges Test beds for spintronic functionalities Challenge: how to go to 300 K with proven functionalities

Y. Siota et al. [Osaka, Tohoku] Nature Mater.2012 Outlook Unanticipated richness of materials science challenges Test beds for spintronic functionalities Challenge: how to go to 300 K with proven functionalities increasing TM/hole concentrations [e.g. (Si,Mn)] ferrimagnetic oxide spinels, TC up to 800 K ferromagnetic metals, TC up to 1200 K condensed magnetic semiconductors -- exploiting attractive forces between TM cations antiferromagnetic spintronics  no cross-talking between bits  can be switched by electric current cf. Andrei Zenkevich Y. Siota et al. [Osaka, Tohoku] Nature Mater.2012

Magnetoresistance hysteresis n-Zn1-xMnxO:Al, x = 0.03 D 50mK 60mK 75mK 100mK 125mK 150mK 200mK TC = 160 mK Rxx () D (mT) Magnetic field (T) Temperature (K) M. Sawicki, ..., M. Kawasaki, T.D., ICPS’00

Replacing lithography by self-assembling top-down  bottom up nanocomposites assembled with atomic precision

Nanospintronics Nanoelectronics = manipulation with charges and currents at nanoscale Nanospintronics = manipulations with magnetisation and spin currents at nanoscale

Universal memory – STT MRAM scalable nonvolatile > 10 yr fast ~ ns endurable 1015 radiation hardness Will replace HD and SSD (flash)?

Low-power logic-in-memory CoFeB Ru MgO ferromagnetic MTJ semiconductor CMOS 4 MTJs + 32 MOSs Adder: power consumption reduced 4 times S. Matsunaga et al. (Tohoku) APEX’08