Chemistry Reference
In-Depth Information
where
T
is time, Τ
sf
is the spin coherent time and
D
is a diffusion constant, the
spin diffusion constant
D
(=2.1 × 10
-2
m
2
/s), spin flip length Λ
sf
(=1.6 Μm),
spin coherent time Τ
sf
(=120 ps), and spin polarization
P
(=0.09) was
estimated, although it should be noted that this is an approximate estimation
because the Eq. (2) is the only existing expression for the estimation of spin
transport properties in the case of the Hanle type spin precession. The
observed spin coherence is almost same as that reported in SLG [11], and
how to enhance the coherence is the next important milestone.
Finally, a prototypical graphene spin transistor operation using SLG is
introduced. So far, there were several reports on gate-voltage-induced
modulation of spin voltages in SLG spin valves [11, 12]. According to a
theory [19], non-local spin voltage exhibits the following relationships with
conductivity of a nonmagnetic channel as the contact between ferro- and
non- magnets changes:
for an Ohmic contact,
2
2
P
R
L
F
−
1
(~ Σ
N
)
∆
V
=
(
)
R
⋅
[sinh(
)]
⋅
I
,
(3)
NON LOCAL
-
F
INJECT
2
2
(1
−
P
)
R
Λ
N
SF
for a tunneling contact
2
∆
V
1
P
Λ
L
SF
= ∆
R
=
exp(
−
).
(4)
NON LOCAL
-
I
2
Σ
A
Λ
N
SF
When we look back a previous study [11], the gate-voltage dependence of
the spin voltage in SLG spin valves with Al-O tunneling barriers exhibited
an opposite dependence as the theory predicts, namely, the spin voltage was
the smallest at the Dirac point where the conductivity of the SLG was the
minimum although the Al-O tunneling barrier was inserted between Co and
SLG. In the other study, the spin voltage had no obvious gate voltage
dependence. In this sense, it can be said that there is much room for
investigation of gate-voltage dependence of spin signals in SLG spin valves.
We have designed our SLG spin valves as they have no tunneling barriers,
and examined whether the spin voltages are proportional or inversely
proportional. Figure 6 (Left) shows the FET characteristics of our SLG, and
the Dirac point was at the gate voltage of ~5 V. The suppression of the
