MOMENT Materials for Optical, Magnetic, and Energy Technologies - PowerPoint PPT Presentation

MOMENT Materials for Optical, Magnetic, and Energy Technologies Semiconducting and half metallic Heusler compounds for multifunctional applications Claudia Felser

JST-DFG 2009 Heusler Compounds as Multifunctional Materials 1905 • Magnetic material: Cu 2 MnAl 1983 • Halfmetallic ferromagnet: NiMnSb • Magneto-optical: PtMnSb • Magneto-mechanic: Ni 2 MnGa • Superconductor: Pd 2 YSn • Semiconductors: CoTiSb • Heavy fermion: Fe 2 VAl • Li-conductor: LiMnSb • Magneto-electronic: Co 2 FeSi 2001 • Thermo-electric: TiNiSn • Magneto-caloric: CoMnSb:Nb

JST-DFG 2009 • Concept • Semiconducting Half Heusler •Thermoelectric materials •Diluted Semiconductors • Half metallic Heusler compounds •High Curie temperatures •Ferrimagnets • High energy photoemission for Devices • Summary

JST-DFG 2009 • Concept • Semiconducting Half Heusler •Diluted Semiconductors •Thermoelectric materials • Half metallic Heusler compounds •High Curie temperatures •Ferrimagnets • High energy photoemission for Devices • Summary

JST-DFG 2009 Rational Design Half metallicity High density of states at E F Large MR at room temperature Intermag 2002: Co 2 Cr 0.4 Fe 0.6 Al CCFA • First TMR device (Inomata et al.) 19% at RT • TMR-device with MgO (Marukame et al. APL 90 (2007) 012508) ⇒ 109% TMR at RT 88 % spin polarisation at 4K • Point contact 80% MR (Coey et al.) Patent (Felser, Block, DE 101 08 760, H01 L43/08 ) Block, Felser, et al. J. Solid State Chem. 176 , 646 (2003)

JST-DFG 2009 Semiconducting Heuslers – Stuffed ZnS Synthesis XYZ X 2 YZ Si 2 Li 2 Cu Sb 2*1 + 11 + 5 = 18 Ga As Al Fe 2 V 3 + 5 = 8 2*8 + 5 + 3 = 24 Co Ti Sb additional t 2 -levels 9 + 4 + 5 = 18

JST-DFG 2009 Slater-Pauling Rule Magic valence electron number X 2 YZ 24 Valence electrons =^24 + sat. magnetization E F Co 2 FeAl 2*9 + 8 + 3 = 29 Ms = 5 μ B Kübler 1983 Galanakis et al., PRB 66 , 012406 (2002) B. Balke et al., Sci. Technol. Adv. Mater. 9 (2008) 014102.

JST-DFG 2009 • Concept • Semiconducting Half Heusler •Thermoelectric materials •Diluted Semiconductors • Halfmetallic Heusler compounds •High Curie temperatures •Ferrimagnets • High energy photoemission for Devices • Summary

JST-DFG 2009 Half Heusler: 18 valence-electrons Thermoelectrica 1,8 Typ Material Price in $/kg Bi 2 (Te 0.8 Se 0.2 ) 3 (metals ) 1,6 CoSb 3 V-VI Bi 2 Te 3 140 (Zr 0.5 Hf 0.5 ) 0.5 Ti 0.5 NiSn 0.998 Sb 0.002 1,4 IV-VI PbTe 99 Figure of merit Z T Si 0.8 Ge 0.2 Zn 4 Sb 3 Zn 4 Sb 3 4 1,2 (Hf 0.5 Zr 0.5 )NiSn (OFZ) Silicides p-MnS i1.73 24 Mg 2 Si 0.8 Sn 0.2 n-Mg 2 Si 0.4 Sn 0.6 18 1,0 Si 0.80 Ge 0.20 660 0,8 Si 0.94 Ge 0.06 270 Skutterutides CoSb 3 11 0,6 Half-Heusler TiNiSn 55 n/p-Clathrate Ba 8 Ga 16 Ge 30 1000 0,4 without Ba 0,2 Oxides p-NaCo 2 O 4 , 17 without Na, O 0,0 Zintl Phasen p-Yb 14 MnSb 11 92 0 200 400 600 800 1000 Th 3 P La 3-X Te 4 160 4 Temperature T K Information H. Böttcher R. Asahi et al. J. Phys.: Cond. Mat. 20 (2008) 64227 K. Miyamoto et al. Appl. Phys. Express 1 (2008) 081901 E. Toberer, Nature Mat. 7 (2008) 105 VK Zaitsev et al. PRB 74 (2006) 045207

JST-DFG 2009 Half Heusler for Thermoelectrics 40 (a) VFeSb TiCoSb YNiSb 30 Survey on HiTT –Materials 20 −1 ) 10 −1 cell 0 DOS (states eV 40 (b) TiCoSb VCoSn NbCoSn 30 20 (Zr 0.5 Hf 0.5 )Ti 0.5 NiSn 0.998 Sb 0.002 -1 ] 0 10 Seebeck coefficient S (T) [ μ VK TiCo 0.93+x Sb -100 TiCoSb 0.95 Bi 0.05 0 −6 −4 −2 0 2 4 6 -200 energy (eV) -300 α : Seebeck coeffizient α 2 σ -400 = σ : Electrical conductivity ZT T -500 λ λ : Thermo conductivity -600 T: Temperatur (K) 0 100 200 300 400 500 600 700 800 Temperature T [K] Kandpal et al. J. Phys. D 39 (2006) 776 Balke et al. PRB 77 , 045209 (2008)

JST-DFG 2009 Thermoelectrica (Zr 0.5 ;Hf 0.5 )Ti 0.5 NiSn 0.998 Sb 0.002 10 TiCo 0.93+x Sb Thermal conductivity κ (T) Resistivity R (T) [ μΩ m] TiCo 0.4 Ni 0.6 Sb 0.4 Sn 0.6 8 1000 (Zr 0.5 Hf 0.5 ) 0.5 TiNiSn 0.998 Sb 0.002 TiCoSb 6 TiNi 0.9 Co 0.1 Sn 0.9 Sb 0.1 -1 ] -1 K TiCo 0.93+x Sb 100 4 [Wm 2 10 0 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 Temperature T [K] Temperature T [K] Improvement of the thermal conductivity 40000 (220) Substrate Substrate 35000 Melt Spinning 30000 Ball milling – Spark Plasma TiNiSn on Al 2 O 3 Int. (cps) 25000 Multilayer 20000 measured data 35000 Lorentz fit 30000 15000 25000 Int. (cps) Nanoparticles 20000 FW HM: ~0.86 15000 10000 10000 Rattlers such as Lithium-Ions 5000 5000 0 19 20 21 22 23 24 ω (°) 0 30 40 50 60 70 80 90 2 θ (°) Barth et al., in preparation (2009)

JST-DFG 2009 First Heusler Nanoparticles: Co 2 FeGa 100 nm 50 nm 10nm 10 nm Basnit et al. J. Phys. D, (2009) accepted

JST-DFG 2009 For Spin Injection XMCD-Investigation on Fe Kroth et al. APL 89 202509 (2006 ) Balke et al. PRB 77 , 045209 (2008)

JST-DFG 2009 Design of Diluted Semiconductors Sb As Mn Si Ti Fe/Mn Ga Co

JST-DFG 2009 • Concept • Semiconducting Half Heusler •Diluted Semiconductors •Thermoelectric materials • Half metallic Heusler compounds •High Curie temperatures •Ferrimagnets • High energy photoemission for Devices • Summary

JST-DFG 2009 Tunneljunction 600 500 400 TMR [%] 300 200 100 0 0 50 100 150 200 250 300 Temperature [K] Co 2 MnSi Al 2 O 3 Co 2 MnSi TMR ratio = 67%@RT, 580%@2K Large temperature dependence of TMR ratio should be solved. et al. APL 89 (2006) 052508 Sakuraba Sakuraba et al. APL 88 (2006) 192508

JST-DFG 2009 Hal f m et al l i c f er r om agnet s - f or Tunnel m agnet or esi st ance TM R - f or CPP G M R W hat do we need? Hi gh Cur i e Tem per at ur e O r der ed L2 1 st r uct ur e G ood i nt er f aces Adj ust ed E F : m i ddl e of t he gap no m agnons Desi gned el ect r oni c st r uct ur e

JST-DFG 2009 High Curie Temperatures Expected Curie temperature for Co 2 : > 1000K FeSi Fecher, J. Appl. Phys. 99 (2006) 08J106 Kübler et al., Phys. Rev. B 76 (2007) 024414

JST-DFG 2009 Co 2 FeSi Hyperfeinfeld (T) Magnetic Moment per unit cell m [ μ B ] 59 Co Spin-Echo Intensity (arb. units) 6 5K 6 8 10 12 14 16 18 20 22 24 26 28 300K 4 775K 2 0 1.0% -2 0.5% 0.0% -4 -0.5% -1.0% -6 -2.0k 0.0 2.0k -3 -2 -1 0 1 2 3 6 A/m] Magnetic Field H [10 120 140 160 180 Frequency (MHz) 60 -1 ] Magnetic moment in saturation: 2 kg σ ( T ) 1/ χ ( T ) 800 5.97 μ B ± 0.1 μ B at 5K Specific Magnetization σ [Am 50 Θ = 1150 ± 50 K T C = 1100 ± 20 K Inverse Susceptibility 1/χ 40 600 Extrapolation to 0K :Slater-Pauling rule: 6 μ B 30 μ 0 H = 0.1T 400 m = 47 μ g Curie Temperature 1120 K 20 T C 200 10 0 0 . 700 800 900 1000 1100 1200 1300 Wurmehl, et al ., APL 88 (2006) 032502 Temperature T [K] Wurmehl, et al ., Phys. Rev. B 72 (2005) 184434

JST-DFG 2009 Heusler in Spintronic Devices: TMR 2 MU28225A470L300-5m223 10 x 10 µm Co 2 FeSi 1-x Al x IrMn 223% 10 CoFe(1) 200 (a) 500 Majority 5 300 K CFAS (5) Resistance ( Ω ) 0 150 TMR ( % ) MgO(2) 400 5 Minority 10 100 CFAS (30) -1 ] 10 300 (b) Spin resolved density of states ρ ( E ) [eV 5 50 0 200 5 0 10 -1000 -500 0 500 1000 10 Field (Oe) (c) 5 TMR: 223%, 300K, A470°C, Rs: 1.74e+02 Ω, RA: 1.74e+04 Ω⋅ µm 2 0 2 MU28-2-25A470L007-2m423 10 x 10 µm 5 10 1000 423% 400 10 (d) 5 7 K 800 300 Resistance ( Ω ) 0 TMR ( % ) 5 600 200 10 10 (e) 5 400 100 0 5 200 0 10 -1000 -500 0 500 1000 -10 -5 0 Field (Oe) Energy E − ε F [eV] 2 TMR: 423.40%, 7K, A470°C, Rs: 1.91e+02 Ω, RA: 1.91e+04 Ω⋅ µm Fecher, Felser J. Phys. D 40 1582 (2007) N. Tezuka et al.,Jpn. J. Appl. Phys. 46 , L454 (2007)

JST-DFG 2009 Heusler in Spintronic Devices: CPP-GMR Courtesy of Koki Takanashi, Sendai CoFeB/MgO ‐ MTJ Half ‐ metal + MgO MTJ CoFeB/MgO ‐ MTJ CPP ‐ GMR with half ‐ metal Challenge: fitting spacer Inomata et al. to be published Interlayer exchange coupling!

JST-DFG 2009 Fer r i m agnet s Appl i cat i on: Spi nt or que Com pensat ed f er r i m agnet ? no net m agnet i zat i on t wo m agnet i c subl at t i ces wi t h com pensat i ng m om ent s W ar r en E. Pi cket t Phys. Rev. B 57 ( 1998) 10613.

JST-DFG 2009 Spin transfer switching Sloczewski 1996 m 1 m 2 J ≈ 100 MA/cm 2 1 – e J ≈ ― α M s H U d ħ g of α reduction & M S Courtesy after Shigemi Mizukami

JST-DFG 2009 Halfmetallic Ferrimagnet Kübler’s Rule Slater Pauling Rule Mn 2 MnGa Two magnetic sublattice 0 μ B •24 Valence electrons – μ B •Mn 3+ at octahedral site – 4 •Mn compensates ⇒ Compensated ferrimagnet Wurmehl, et al. J. Phys. Cond. Mat . 18 (2006) 6171 Balke et al. APL 90 (2007) 152504

JST-DFG 2009 Compensated Ferrimagnet: Heusler Mn 2 MnGa Low Moment – High Curie Temperature: low current for spinswitch Tetragonal distorted Heusler: Mn 3+ Jahn Teller Ion Compensated ferrimagnet: 1 μ B Theoretical Spinpolarisation: 88% Curie temperature: 730 K Balke et al. APL 90 (2007) 152504 Winterlik et al. Phys. Rev. B 77 (2008) 054406

JST-DFG 2009 Heusler and relates Structures X 2 MnZ XMnMnZ XCrCrZ