effect of graphene incorporation on spin dynamics of ...web.iitd.ac.in/~sujeetc/best poster rahul...
TRANSCRIPT
Rahul Gupta1*,Akash Kumar1, Saroj Dash2, Sujeet Chaudhary1 and Pranaba Kishor Muduli1
1Department of Physics, Indian Institute of Technology, Hauz Khas, New Delhi-110016, India 2Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden
*E-mail: [email protected]
Abstract:
We report on the ferromagnetic resonance (FMR) spectra of Permalloy (Py)/ Graphene (Gr) and pure Py thin films grown under identical conditions to study the phenomena
of spin pumping into Graphene. An enhancement of Gilbert damping constant is observed for Py/Gr bilayer structure. Using detailed thickness dependence study we show
an enhancement of spin mixing conductance of Ta/Py/Gr/SiO2/Si compared to Ta/Py/SiO2/Si, which can be attributed to spin pumping. This study is important for successful
integration of graphene with commonly used ferromagnetic materials for spintronics applications.
Introduction
Ferromagnetic Resonance
X-ray Reflectivity Raman Spectroscopy
Experimental set-up
Acknowledgement
I would like to acknowledge Nano Research Facility (NRF) and Central Research Facility (CRF), IIT Delhi and Thin Film Laboratory, IIT Delhi for facilities.
Conclusion References
0.5 1.0 1.5 2.0 2.5 3.010
-2
10-1
100
101
102
103
104
105
106
107 Ta/Py(10nm)/SiO
2/Si
Fitted
Ref
lect
ivit
y (
R)
2 (deg.)
Material
Used
Thickness
(nm)
Roughness
(nm)
SiO2 600000 0.4
Py 10 1. 4
Ta 0.6 0.7
Ta2O5 2.1 0.97 1500 2000 2500 3000
0
50
100
150
2002D = 2694.78 cm
-1 Gr/SiO
2
Fitted
Inte
nsi
ty
Raman Shift (cm-1
)
G = 1589.99 cm-1
0
40
80
0
40
80
1500 2000 2500 30000
40
80
p=2mTorrD
G 2D
=514nm
Inte
nsi
ty (
a.u.)
p=6mTorr
p=10mTorr
Raman Shift (cm-1)
J. Hirsch, Phys. Rev. Lett. 83, 1834 (1999).
A. Brataas, Y. V. Nazarov, and G. E. W. Bauer, Phys. Rev. Lett. 84, 2481 (2000).
Will Gannett et al., J. Appl. Phys. 117, 213907 (2015).
Wei Han et al., Nature Nanotechnology 9, 794-807 (2014).
A. K. Patra, S. Singh, B. Barin, Y. Lee, J.-H. Ahn, E. del Barco, E. R. Mucciolo, and
B. Özyilmaz, Appl. Phys. Lett. 101, 162407 (2012).
A large increase of Gilbert damping constant in Ta/Py/Gr/SiO2/Si as
compared to Ta/Py/SiO2/Si thin film was observed which signifies spin
pumping into graphene. The calculated value of spin mixing conductance
(g↑↓) of Ta/Py/Gr/SiO2/Si is found to be (2.621±0.001)⨯1018 m-2.
We also find that the quality of Py films on graphene and without graphene to
be very similar as determined from their material properties. This indicates
that CVD grown graphene can act a good material for spin pumping studies.
Here, we have prepared a
series of samples; bare Py
and Py/Gr by varying
thickness of
ferromagnetic films (Py)
on the SiO2/Si and
Gr/SiO2/Si substrates.
We grow Py thin films by
using DC-magnetron
sputtering at 2 mTorr
Argon working pressure.
A 2 nm of Tantalum (Ta)
capping layer is also
deposited for protection
of samples from
oxidation.
We have performed the FMR spectroscopy at room temperature for
excitation frequency of 4-12 GHz using a broad-band FMR set-up
as shown in above figure.
The FMR set up is based on the Co-planar waveguide (CPW).
The excitation of spin angular momentum can be measured by
FMR spectroscopy.
The commercial
graphene samples
used in this work
were prepared by
chemical vapour
deposition
[Graphenea, Spain].
The Raman Spectra of monolayer graphene is show that the G-peak (=1589.99 cm-1) and
2D-peak ( =2694.79 cm-1)is observed as cited in the literature.
The Raman spectra of Py deposit on the top of Graphene at different Argon working
pressure is shown in figure. The G-peak and 2D-peak still observed whereas an additional
peak, called Defect-peak (= 1351.54cm-1 ), is also observed. The intensity of D-peak
increases as the Argon working pressure decreases.
The X-ray reflectivity tells the thickness and
roughness of thin film.
Here, we have taken the XRR for the
Ta/Py/SiO2/Si sample. The table given below
tells thickness and roughness of thin films in
the bilayer structure.
Kittle Formula Line width FWHM
4 6 8 10 12
1.5
2.0
2.5
3.0
3.5
4.0
4.5
H
(m
T)
frequency (GHz)
Ta/Py(10nm)/Gr/SiO2/Si
100 110 120 130 140
Ta/Py(10nm)/Gr/SiO2/Si
Ta/Py(10nm)/SiO2/Si
FM
R S
ig.
(a.u
.)
Field oH (mT)
Model Derivative_FMR (User)
Equation2*A*dH^2*(x-Hr)/(dH^2+(x-Hr)^2)^2+S*(dH^2
-(x-Hr)^2)/(dH^2+(x-Hr)^2)^2+m*x+c
Reduced
Chi-Sqr
166.57081
Adj. R-Square 0.99944
Value Standard Error
FMR Signal
with
Hr 1178.44211 0.12476
dH 36.16466 0.12889
A -58605.98552 318.77723
S -1.54831E6 13930.26903
m 0.03072 0.01478
c 24.25084 17.28415
Model Derivative_FMR (User)
Equation2*A*dH^2*(x-Hr)/(dH^2+(x-Hr)^2)^2+S*(dH^2
-(x-Hr)^2)/(dH^2+(x-Hr)^2)^2+m*x+c
Reduced
Chi-Sqr
595.33569
Adj. R-Square 0.99629
Value Standard Error
FMR Signal
without
Hr 1154.31923 0.27473
dH 30.96489 0.27966
A -48522.18297 428.07507
S -260987.9608
8
21978.39939
m 0.00557 0.02719
c 55.11754 31.81767
Hr = (117.84 0.012) mT
Hr = (115.43 0.027) mT
f = 10 GHz
( )
( )
Ta/Py(10nm)/SiO2/Si
4
6
8
10
12
0 30 60 90 120 150 180
freq
uen
cy
(G
Hz)
Ta/Py(10nm)/Gr/SiO2/Si
Meff
= (66.965 0.057) mT
Meff
= (69.589 0.038) mT
Hr (mT)
Ta/Py(10nm)/SiO2/Si
0.05 0.10 0.15 0.20 0.25 0.30 0.3540
45
50
55
60
65
70
75 Ta/Py(t)/Gr/SiO
2/Si
Ta/Py(t)/SiO2/Si
Mef
f (m
T)
1/tPy
(nm-1
)
Ms = 77.5 0.8 mT
Ms = 79.2 0.6 mT
0.05 0.10 0.15 0.20 0.25 0.30 0.35
8
12
16
20
24Ta/Py(t)/Gr/SiO
2/Si
Ta/Py(t)/SiO2/Si
Dam
pin
g C
ons.
(10
-3)
1/tPy
(nm-1
)
g = (2.621 0.001)1018
m-2
g = (1.19 0.0002)1018
m-2
2 4 6 8 10 12 14 16-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
H
o (m
T)
tPy
(nm)
Ta/Py(t)/Gr/SiO2/Si
Ta/Py(t)/SiO2/Si
Heff
-M×H
D
M
Magnetization damping term
Dissipation of angular momentum
Transferred to conduction electrons
Generation of spin current
*Landau-Lifshitz-Gilbert equation
The damping of magnetization term is introduced by Gilbert*
When FM/NM interface is formed electrons
losses it’s spin angular momentum via s-d
interaction, known as spin pumping.
Spin pumping generates spin current though
FM/NM interface.
Spin mixing conductance
DC-magnetron Sputtering System Ferromagnetic Resonance
𝑓 = 𝛾
2𝜋[(𝐻𝑟 + 𝐻𝑘)(𝐻𝑟 + 𝐻𝑘 + 4𝜋𝑀𝑒𝑓𝑓)] ∆𝐻 =
4𝜋𝛼
𝛾𝑓 + ∆𝐻0
∆𝛼 = 𝑔𝜇𝐵
𝑔↑↓
4𝜋𝑀𝑠
1
𝑡𝐹𝑀
Where,
𝑔↑↓ = Spin Mixing Conductance
Using Line-width and Kittle formula given above, we have fitted the data and get
the Gilbert damping constant & effective magnetization.
The FMR absorption spectra for Py sample with graphene is fitted with the
derivative of Lorentzian function to determine FMR linewidth (∆𝐻) and resonance
field (𝐻𝑟).
𝑑𝑀
𝑑𝑡= −𝛾𝜇0𝑀 × 𝐻𝑒𝑓𝑓 −
𝛾𝛼
𝑀 [𝑀 × (𝑀 × 𝐻𝑒𝑓𝑓)]
𝐽𝑠𝑝𝑢𝑚𝑝
= ℏ
4𝜋𝑔↑↓[𝑀 ×
𝑑𝑀
𝑑𝑡]
Effect of Graphene Incorporation on Spin Dynamics of Permalloy Thin Film