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2018.06.12 paolo perna imdea NanoFrontMag

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II Jornada científica NanoFrontMag - 12 de junio de 2018 - IMDEA Nanociencia
Paolo Perna
Grupo GNB-IMDEA

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2018.06.12 paolo perna imdea NanoFrontMag

  1. 1. 13/06/2018 P. Perna - 58th MMM Denver, CO 1 IIJornadacientíficadeNanoFrontMag Paolo Perna SpinOrbitronics Group @ IMDEA-Nanoscience, Madrid, Spain CM Project NANOFRONTMAG-CM EU FLAGERA SOgraph (MINECO PCIN-2015-111) H2020-FETOPEN ByAXON (2017-2022): Towards an active bypass for neural reconnection MINECO FIS2016-78591-C3-1-R SKYTRON FIS2015-67287-P LANTHACOOR FIS2013-40667-P FUNCGRAPHENE
  2. 2. 12/06/2018 2 Adapted from A. Soumyanarayanan, et al. Nature 539, 509 (2016) Spin-Orbitronics From PhD thesis, Paolo Perna, 2008 P. Perna
  3. 3. 12/06/2018 Creating a giant Spin Orbit Coupling in graphene Why Graphene ? Long spin diffusion length Long spin lifetime But … negligible SOC !!! Spintronics, Spin-Orbitronics devices Induce SOC in gr by metal intercalation, mol. functionalization, … F. Calleja et al. Nat. Phys. (2015) 11, 43 M. Garnica, et al. Nat. Phys. (2013) 9, 368 D. Maccariello et al. Chem. Mat. (2014) 26, 2883 Gr/Pb/Ir(111) Pb-intercalated Gr / Ir(111) by STM P. Perna
  4. 4. 12/06/2018 Creating a giant Spin Orbit Coupling in graphene Why Graphene ? Long spin diffusion length Long spin lifetime But … negligible SOC !!! Spintronics, Spin-Orbitronics devices Otrokov et al. 2D Mater. 5 (2018) 035029 Induce SOC in gr by metal intercalation, mol. functionalization, … Pb-intercalated Gr / Ir(111) by ARPES n-doped ED= -250 meV hν=21.2 eV Spin-split Graphene bands by a Giant Spin Orbit interaction induced by Pb atoms  Absence of FM  Growth of Graphene on single crystals surfaces P. Perna
  5. 5. P. Perna13/06/2018 • Choose of the suitable oxide substrate: MgO(111), STO(111), Al2O3(0001) • Sputtered Pt epitaxial buffers on insulating crystals @ 500 ºC • In-situ UHV CVD gr growth @ 750 ºC • Evaporation & Intercalation of Co @ RT • Monitoring by XPS and LEED at each stage • Avoiding Co/Pt intermixing NM1 FM NM2 Pt (111) on (111)-oxides Co layer (PMA) ML graphene (111)-oxide 70 eV (111)-oxide Pt (111) 100nm (111)-oxide Pt (111) 100nm Co layer (PMA) ML graphene (111)-oxide Pt (111) 100nm ML graphene (111)-oxide Pt (111) 100nm Co layer (PMA) Co intercalated graphene on Oxide
  6. 6. P. Perna High Resolution TEM & EELS • FCC Co • Pseudomorphic with Pt • No dislocations • Few stacking faults • No Co/Pt intermixing • Co fully strained in plane to match Pt • Effective protection of gr first STEM images acquired in gr-based magnetic heterostructures 13/06/2018 6 M. Varela, UCM 20nm 20nm 2nm 2nm F. Ajejas, PP et al. arXiv:1803.07443 (2018)
  7. 7. 12/06/2018 7 288 287 286 285 284 283 282 281 raw data gr-Pt C-H HOPG gr-Pt Co-gr-Pt gr-Co ∆E ~ 0.5 eV C 1s B.E. (eV) Intensity(a.u) Pt (111) MgO (111) gr Co Pt (111) MgO (111) gr Co Pt (111) MgO (111) gr EF EF a1 a2 a3 b1 b2 b3 in-situ X-Ray Photoemission Spectroscopy (XPS) Electric field perpendicular to the interface BE=284.0 eV (C1s gr-Pt): sp2 hybridization C-C bonding on Pt(111) BE=284.5 eV (C1s gr-Co) Co-C bonding F. Ajejas, PP et al. arXiv:1803.07443 (2018) p-doped gr on Pt n-doped gr on Co P. Perna
  8. 8. 12/06/2018 88 -150 0 150 -150 0 150 -150 0 150 -150 0 150 -150 0 150 -150 0 150 µ0Hz (mT) Mz(PolarKerrInt.) 5 MLs 10 MLs 20 MLs gr / Co (t) / Pt(111) a1 a2 a3 a4 a5 a6 15 MLs 25 MLs 30 MLs -4 -2 0 2 4 -1 0 1 µ0Hin-plane (T) Min-plane/MS b HK 5 MLs 0 5 10 15 20 25 30 0.0 0.5 1.0 cMz,rem/MS tCo (MLs) gr/Co/t)/Pt(111) Pt/Co(t)/Pt Enhanced PMA for Co thickness up to 4 nm → Different Magnetization Reversal Mechanisms → Large PMA extended up to 20MLs Co (non-epitaxial samples spin-reorientation at 7 MLs) → on oxide substrates (avoid leakage current in devices) On Ir(111) single cristal spin reorientation at 13MLs On Pt(111) single cristal spin reorientation at 12MLs Yang et al. Nano Lett. 16 (2015) 145 Scie. Rep. 6 (2016) 24783 Stohr, JMMM 200 (1999) 470 HK = 2T ; Msat = 1.3 MA/m = 1.56 μB/atom  K0 = MSHK/2 = 1.3 MJ/m3 F. Ajejas, PP et al. arXiv:1803.07443 (2018)P. Perna
  9. 9. 0 2 4 6 8 770 780 790 800 810 -4 -3 -2 -1 0 1 XAS(a.u.) +6T pos. rem. XMCD(a.u.) E (eV) RT 0 2 4 6 8 770 780 790 800 810 -4 -3 -2 -1 0 1 XAS(n.u.)XMCD(a.u.) +6T E (eV) RT µ0H µ0H Giant orbital magnetic moment of fcc Co @ RT PMA = 0.16 meV/Co-atom ( 1.3 MJ/m3) Unusual large perp orbital moment @ RT PMA of Co(111) films sandwiched between gr and Pt(111) is due to the large anisotropy of the orbital moment. Enhancement of PMA due to hybridization between dyz and dz 2 orbitals with π state of gr as suggested by first principle simulation in Ir(111) single crystals Yang et al. Nano Lett. 16 (2015) 145 m┴ L/m┴ S = 0.15 >> m║ L/m║ S = 0.11 hcp Co bulk mbulk L/mbulk S = 0.10 SO anisotropy: ΔmL/nh = (m|| L - m┴ L)/nh If nh = 2.49  ΔmL/nh = 0.11 µB/atom (~0.16 meV/Co-atom) 12/06/2018 99 µ µ µ- µ µ µ µ- µ L3 L2 L3 L2 F. Ajejas, PP et al. arXiv:1803.07443 (2018)P. Perna
  10. 10. 12/06/2018 10 Interfacial Dzyaloshinskii-Moriya Interaction  DMI interaction is due to SOC  Induce canting in spins  Fixed chirality in domain wall  The stability of skyrmions depends on the competition between D and uniaxial anisotropy Fert et al. Nat. Nano 2010 −𝐽𝐽 ∑𝑖𝑖𝑗𝑗 𝑺𝑺𝑖𝑖 � 𝑺𝑺𝑗𝑗 − ∑𝑖𝑖𝑗𝑗 𝑫𝑫𝑖𝑖𝑖𝑖 � 𝑺𝑺𝑖𝑖 × 𝑺𝑺𝑗𝑗 Ultrathin FM (e.g. Co) with PMA + large SOC material (e.g. Pb, Pt) DMI is an antisymmetric indirect exchange between two spins coupled by the strong SOC of a third atom Technological breakthroughs: - Stable @ RT (topological protected) - Size (~20-100 nm) - Short separations (large density) - Fast inform. transfer @ ~ current - ~ inform. transfer @ smaller current D. Maccariello et al. Nature Nanotech. (2018); DOI: 10.1038/s41565-017-0044-4 Skyrmions jc,sk ~ 106 Am-2 vsk ~ 10-4 ms-1 DWs jc,sk ~ 1011-1012 Am-2 vsk ~ 10-100 ms-1 Rohart et al PRB 88, (2013) 184422 Dzyaloshinskii, Sov. Union JETP, 5 (1957) 1259 Moriya, Phys. Rev. 120 (1960) 911 P. Perna
  11. 11. 12/06/2018 11 Sizeable effective DMI Deff = 0-DMI1 +DMI1 NM1 FM NM1 BLOCH type DWs Symmetric interfaces DMI2 DMI1 NM2 FM NM1 Deff ≠ 0 chiral NÉEL type DWs NM2 FM NM1 DMI1 DMI2 CCW CW NM1: Pt  NM2: Ir, Cu, Al, gr D1>D2 Asymmetric interfaces P. Perna F. Ajejas, et al., Appl. Phys. Lett. 111, 202402 (2017)
  12. 12. Néel-type Domain Walls (DWs) in gr/Co/Pt 12/06/2018 Measurements of the expansion of bubble domains F. Ajejas, PP et al. arXiv:1803.07443 (2018) 0 100 200 300 400 500 600 700 0 10 20 30 40 50 Pt/Co/Pt µ0Hz (mT) Velocity(m/s) 0 100 200 300 400 500 600 700 0 20 40 60 80 µ0Hz (mT) Velocity(m/s) gr / Co (5 MLs) / Pt(111) creep flow Speed increases linearly Zero DMI Deff = 0 BLOCH type DWs Speed saturates Existence of sizeable DMI Deff ≠ 0 NÉEL type DWs Hz Hz Hz P. Perna F. Ajejas, et al., Appl. Phys. Lett. 111, 202402 (2017)
  13. 13. 12/06/2018 13 Néel-type Domain Walls (DWs) & chirality Measurements of the expansion of bubble domains in presence of an in-plane magnetic field Hx dc Hz Hz Hz Hx dc Chiral Néel DWs Hx dc CCW CW Bloch DWs Hx dc P. Perna
  14. 14. P. Perna F. Ajejas, PP et al. arXiv:1803.07443 (2018)12/06/2018 14 gr/Co/Pt -Bx +BxBz -200 -100 0 100 200 0 20 40 60 80 100 µ0Hx (mT) Velocity(m/s) up/down down/up Bz = 465 mT Pt/Co/Pt -Bx +BxBz Bloch -200 -100 0 100 200 20 30 40 50 60 70 80 µ0Hx (mT) down/up up/down Velocity(m/sec) Bz = 300 mT Determination of DMI value: Minima correspond to the field necessary to compensate DMI Néel-type Domain Walls (DWs) & left handed chirality Measurements of the expansion of bubble domains in presence of an in-plane magnetic field F. Ajejas, et al., APL 111, 202402 (2017)
  15. 15. 12/06/2018 15 gr/Co/Pt -Bx +BxBz -200 -100 0 100 200 0 20 40 60 80 100 µ0Hx (mT) Velocity(m/s) up/down down/up Bz = 465 mT Néel-type Domain Walls (DWs) & left handed chirality Measurements of the expansion of bubble domains in presence of an in-plane magnetic field Asymmetric expansion of DWs Neél DWs with left-handed (CCW) chirality DMI gr/Co OPPOSITE to Co/Pt F. Ajejas, PP et al. arXiv:1803.07443 (2018) Néel-type DWs with CCW chirality P. Perna 𝑫𝑫𝒆𝒆𝒆𝒆𝒆𝒆 = 0.6 ± 𝟎𝟎. 𝟐𝟐 𝒎𝒎𝒎𝒎 𝒎𝒎𝟐𝟐 𝑫𝑫𝑪𝑪𝑪𝑪/𝑷𝑷𝑷𝑷 = 1. 𝟒𝟒 ± 𝟎𝟎. 𝟐𝟐 𝒎𝒎𝒎𝒎 𝒎𝒎𝟐𝟐 ∗ 𝑫𝑫𝒈𝒈𝒈𝒈/𝑪𝑪𝑪𝑪 = 0. 𝟖𝟖 ± 𝟎𝟎. 𝟐𝟐 𝒎𝒎𝒎𝒎 𝒎𝒎𝟐𝟐 ~ 𝟎𝟎. 𝟔𝟔 𝒎𝒎𝒎𝒎𝒎𝒎 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂 * F. Ajejas, et al., APL 111, 202402 (2017)
  16. 16. n-doped graphene Origin of the unusual (large) DMI at gr/Co SOC-DMI at Co/Pt interface Three-sites model (Fert-Levy) based on HM impurities in Co layer Rashba-DMI mechanisms at gr/Co (existence of sizeable electric field) F. Ajejas, PP et al. arXiv:1803.07443 (2018) Nano Letters (2018) 12/06/2018 Fert A. & Levy P. M., Role of Anisotropic Exchange Interactions in Determining the Properties of Spin-Glasses, Phys. Rev. Lett. 44, 1538–1541 (1980). Kundu A. and Zhang S., Dzyaloshinskii-Moriya interaction mediated by spin-polarized band with Rashba spin-orbit coupling, Phys. Rev. B 92, 094434 (2015) F. Ajejas, PP et al. arXiv:1803.07443 (2018)P. Perna
  17. 17. 12/06/2018 Conclusions (1) EU FLAGERA SOgraph (MINECO PCIN-2015-111) MINECO FIS2016-78591-C3-1-R SKYTRON MAT2012-39308 MORGASPIN FIS2013-40667-P FUNCGRAPHENE FIS2015-67287-P LANTHACOOR CM Project NANOFRONTMAG-CM → High quality Gr-based epitaxial stacks on oxides (resembling single crystals) → Enhanced PMA, extended up to 20MLs Co → FCC structure of Co, pseudomorphic with Pt → Unexpected giant DMI with left-handed chirality at gr/Co interface → Rashba-DMI at gr/Co OPPOSITE to SOC-induced Co/Pt → Chiral Spin texture stable at RT and protected by gr n-doped graphene Partners: A. Fert, V. Cros @ CNRS-THALES N. Jaouen @ SOLEIL K. Zvezdin @ IPM P. Perna
  18. 18. 12/06/2018 19 Adapted from A. Soumyanarayanan, et al. Nature 539, 509 (2016) From PhD thesis, Paolo Perna, 2008 Spin-Orbitronics P. Perna
  19. 19. 12/06/2018 20 Magnetic Anisotropy dictates both magnetic (reversal) & transport (MR) behaviors AMR∝ cos2 θ Anisotropic Magnetoresistance (AMR) caused by the Spin-Orbit (SO) interaction that induces the mixing of spin-up and spin-down states. It depends on the relative orientation between the magnetization vector M and the injected current J, giving rise to a magnetization-direction dependent scattering rate. θ = <J,M> αH= 0º e.a. M(n.u.) µ0H (mT) Anisotropic Magnetoresistance (AMR) h.a. αH= 90º FM Uniaxial FM FM: Below Tc spins are aligned parallel Grown under H (or @ oblique incidence) KU MR(n.u.) µ0H (mT) J µ0H P. Perna PP et al. APL 104, 202407 (2014) Rev. Sci. Instrum. 85, 053904 (2014) PRB 86, 024421 (2012) PRB 92, 220422(R) (2015)
  20. 20. 12/06/2018 22 MR response in La0.7Sr0.3MnO3 Four-fold (bulk) magneto-crystalline anisotropy Isotropic behavior @ RT @ LT -4 -3 -2 -1 0 1 2 3 4 µ0H (mT) [R(H)-R0]/R0(%) CMR + AMR @ RT CMR dominates over AMR at RT < 0.05% P. Perna
  21. 21. 12/06/2018 23 6° (a) 2° (b) [010] [100] 0° (c) 200nm Enhancing AMR by tuning magnetic anisotropy P. Perna et al. Adv. Funct. Mater. 2017, 1700664 anisotropy P. Perna
  22. 22. 12/06/2018 24 i) sign of the ΔR depends on the J direction ii) CMR does not depend neither to J nor the H direction LSMO : Max MR change ~ 0.25% CMR ~ 0.04% @ 20mT AMR vs. CMR P. Perna et al. Adv. Funct. Mater. 2017, 1700664 P. Perna
  23. 23. P. Perna12/06/2018 25 Magnetization Reversal vs. AMR in uniaxial LSMO P. Perna et al. Adv. Funct. Mater. 2017, 1700664
  24. 24. 12/06/2018 26 Getting large AMR in LSMO by nanoengineering of the interface Vicinal surfaces Simultaneous MR-H and M-H measurements Large AMR vs. CMR in on-purpose designed LSMO surfaces Switchable MR for RT devices !!! (not achievable with CMR) P. Perna et al. Adv. Funct. Mater. 2017, 1700664 SrTiO3 (001) PP et al. JAP 110, 013919 (2011) PP et al. JAP 109, 07B107 (2011) PP et al. New J. Phys. 12, 103033 (2010) D. Dadil, PP et al. JAP 112, 013906 (2012) PP et al., PRB 86, 024421 (2012) PP et al., APL 104, 202407 (2014) PP et al., PRB 92 (22), 220422 (2015) P. Perna
  25. 25. Magnetic anisotropy determines the magnetization reversals and MR The simultaneous M-H and MR-H measurements allow for correlating magnetization reversals & MR responses for any field values and directions. 27 Set the desired magnetic anisotropy by employing vicinal surfaces for the LSMO growth Large AMR vs. CMR in on-purpose designed LSMO surfaces P. Perna et al. Adv. Funct. Mater. 2017, 1700664 Switchable MR for RT devices !!! (not achievable with CMR) Conclusions (2) This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 737116 (ByAXON). J90º µ0H (mT) J0º [R(H)-R(0)]/R(0) Norm.Magn. M|| M⊥ µ0H (mT) P. Perna12/06/2018
  26. 26. paolo.perna@imdea.org 28 F. Ajejas, A. Gudín, J.M. Diaz, L. De Melo Costa, P. Olleros, A. Anadon, R. Guerrero, J. Camarero, R. Miranda IMDEA Nanociencia, Madrid, Spain. DFMC, Instituto “Nicolás Cabrera” & IFIMAC, UAM, Madrid, Spain. M.A. Niño, F. Calleja, A. Vazquez de Parga, L. Chirolli, T. González, L. Pérez, J. Pedrosa IMDEA Nanociencia, Madrid, Spain. S. Pizzini, J. Vogel Université Grenoble Alpes, CNRS, Institut Néel, Grenoble, France. M. Valvidares, P. Gargiani ALBA SYNCHROTRON LIGHT SOURCE, Barcelona, Spain. M. Cabero, M. Varela, J. Santamaria UCM, GFMC, DFM, IMA & IP, Madrid, Spain. V. Cros, N. Reyren, D. Maccariello, A. Fert CNRS-THALES, Palaiseau, France. N. Jaouen SOLEIL Synchorotron, Palaiseau, France. K. Zvezdin IPM, Italy L. Méchin, S. Flament CNRS-GREYC & ENSICAEN, Caen, France. K. Guslienko Ikerbasque, University of the Basque Country, UPV/EHU O. Oksana Chubykalo-Fesenko ICMM-CSIC, Madrid, Spain Acknowledgements CM Project NANOFRONTMAG-CM EU FLAGERA SOgraph (MINECO PCIN-2015-111) H2020-FETOPEN ByAXON (2017-2022): Towards an active bypass for neural reconnection MINECO FIS2016-78591-C3-1-R SKYTRON FIS2015-67287-P LANTHACOOR FIS2013-40667-P FUNCGRAPHENE Thank you for the attention !! 12/06/2018

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