II Jornada científica NanoFrontMag - 12 de junio de 2018 - IMDEA Nanociencia Cristina Bran Grupo GMM-CSIC

1. Magnetization Ratchet in Cylindrical Nanowires
Institute of Materials Science of Madrid, ICMM-CSIC
C. Bran, J. A. Fernandez-Roldan, E. M. Palmero, E. Berganza, J. Meier, E. Calle, M. Jaafar,
M. Foerster, L. Aballe, A. Fraile Rodriguez, A. Asenjo, R.P. del Real, O. Chubykalo-Fesenko and
M.Vazquez
cristina.bran@icmm.csic.es

2. 2D Magnetic nanowires => nanostrips
M. Kläui et al., Phys. Rev. Lett. 95, 026601 (2005)
DWs designed by: geometry, material..
DWs controlled by magnetic fields and electrical currents
B. Borie et al., Phys. Rev. Appl. 8,
044004 (2017)
A. Pushp et al. Nature Physics 9, 505(2013).
J.H. Franken at al., Nature Nanotechnology 7, 499 (2012)
cristina.bran@icmm.csic.es
- Pinning by notches in Py strips
- Specific chirality
DWs follow specific paths as function
of chirality
DWs manipulated by rotating magnetic fields
DWs energy engineered to favor a
unidirectional ratchet-like propagation

3. 3D cylindrical nanowires
N. Biziere et al, Nano Lett. 13, 2053(2013)
S. Da-Col et al., Phys. Rev. B 89, 180405(2014)
TDWBPDW
D. Reyes et al, Nano Lett. 16, 1230(2016)
cristina.bran@icmm.csic.es
A. Fernandez-Pacheco et al.,
Scientific Reports 3, 1492
(2013)
NWs in alumina membranes NW growth by FEBID
Advantages:
Tailored DWs
Stability
High velocities
Easy and cheap to fabricate
NW
shadow
C. Bran et al. Phys. Rev. B 96, 125415 (2017)

4. 3D cylindrical nanowires
z
y
x
Transverse Domain Wall
mz
-1
0
1
H
Vortex (Bloch Point) Domain Wall
Tail-to-tail Head-to-head
DWs determined by geometry and material
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5. Domain Wall (DW) manipulation
Full control over DW is required for
information storage technologies,
logic systems and sensors.
Magnetic Racetrack Memory
Stuart Parkin. Science 320 (2008)
Magnetic Logic Circuit
D. Allwood et al. Science 309 (2005)
MOTIVATION
DWs
Well defined
Full control
Evaluate the possibility to control DWs by means of a diameter-
modulated geometry and tailored anisotropy.
Objetive
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6. • Anodic Aluminum Oxide (AAO) template
• Mild and Hard Anodization (HA)+pulses
• rapid growth
• ordered pores with D=20-200 nm
0 1000 2000 3000 4000
-20
0
20
40
60
80
100
120
140
160
0 1000 2000 3000 4000
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
I(mA)
time (s)
0
30
60
90
120
150
V(V)
Voltage(V)
Time (s)
Type A
0 2000 4000 6000 8000
-20
0
20
40
60
80
100
120
140
160
2000 3000 4000 5000 6000 7000 8000
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
I(mA)
time (s)
-20
0
20
40
60
80
100
120
140
V(V)
(C)
(B)
Voltage(V)
Time (s)
(A)
Type B or C
Synthesis and preparation
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7. Type A: D=20-250nm, L1>20um
Type B: D1=130nm, D2=140nm, L1=4-800nm
L2=<50nm
Type C: D1=130nm, D2=100nm, L1=200-1000nm
L2=200-500nm
Synthesis and preparation
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8. 30 nm Cu30 nm Cu
FeCo=300-900 nm
30 nm Cu
Multisegmented nanowires
FMNM
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9. C. Bran et al, ACS Nano 2018
DOI: 10.1021/acsnano.8b02153
MOKE measurements
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Long.Kerr(normalized)
360 Oe
260 Oe
195 Oe
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Long.Kerr(normalized)
275 Oe
363 Oe
260 Oe
-400 -200 0 200 400
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Long.Kerr(normalized)
H (Oe)
365 Oe
265 Oe
Multisegmented nanowires
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10. XMCD-PEEM measurements
NW
shadow
DW M
NW
shadow
Magnetic field
Multisegmented nanowires

11. XMCD-PEEM measurements (in remanence)
XAS
Unidirectional Ratchet–like DW
propagation
H
Multisegmented nanowires
cristina.bran@icmm.csic.es
C. Bran et al, ACS Nano 2018
DOI: 10.1021/acsnano.8b02153

12. XMCD-PEEM measurements (in remanence)
XAS
Multisegmented nanowires
-900 -600 -300 0 300 600 900
-1.0
-0.5
0.0
0.5
1.0
M/Ms
Applied field (Oe)
H
cristina.bran@icmm.csic.es
C. Bran et al, ACS Nano 2018
DOI: 10.1021/acsnano.8b02153

13. H
Simulations: J.A. Fernandez-Roldan and O. Chubykalo-Fesenko
Multisegmented nanowires
200 250 300 350 400 450 500 550
30 Msat = 2.00 T;
Aex = 25.0e-12 J/m
Kc1 = 1.0e4 const. J/m3
grainsize := 5.0e-9 ;
UNITS: nm.
Length: 3210
Diameter: 80
FeCo
Cu
PARAMETERS (FeCo)
cristina.bran@icmm.csic.es
J. A. Fernandez-Roldan, R. Perez del Real, C. Bran, M. Vazquez and O. Chubykalo-Fesenko, Nanoscale, 2018
A.Vansteenkiste et al.,The design and verification of mumax3, AIP Advances 4, 107133 (2014).

14. -1200 -600 0 600 1200
-1,0
-0,5
0,0
0,5
1,0
-510 -425 -340
-1
0
1
m(a.u)
H(Oe)
m(a.u.)
H(Oe)
b
c
d
e
e) H = - 460 Oe
L
R
c) H = - 425 Oe
L
R
b) H = - 360 Oe
x
y
z
z
y
bc
d
e
L
R
d) H = - 445 Oe
Pinned
a
1
0
-1
mx
a) H = 0 Oe
x
y
z
z
y
H

15. 15
Total and internal magnetic energies in the NW as function of the longitudinal magnetization
The configurations b-d are dynamical and do not correspond to true minima of the total energy
In real experimental those configurations may be stabilized by the presence of defects.
Multisegmented nanowires-Micromagnetic simulations
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16.  Unidirectional and step-like propagation
 The reversal is often pinned at specific locations associated with Cu layers
 The reversal process starts in the shortest segment
 Micromagnetic simulations->complex process: sequential switching, formation of vortices
and skyrmion tube states
 Remagnetization ratchet is induced by the variable length of the segments
J. A. Fernandez-Roldan, R. Perez del Real, C. Bran, M. Vazquez and O. Chubykalo-Fesenko,
Nanoscale, 2018
C. Bran et al. ACS Nano 2018
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XMCD-PEEM capable to determine the magnetization distribution at the surface and inside the
NW
Conclusions