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

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. P. Perna12/06/2018 25
Magnetization Reversal vs. AMR in uniaxial LSMO
P. Perna et al. Adv. Funct. Mater. 2017, 1700664

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. 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. 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