Supplementary Information.
I. Rubrene nanowire array embedded in AAO (anodic aluminum oxide) template.
As shown in the cross-sectional Field Emission Scanning Electron Microscopic (FESEM)
image in Figure 1 of the main text, rubrene nanowires are very uniform and they completely fill
the nanopores hosted in the AAO template. To confirm the uniformity of the nanowires at the
pore bottom, we have exposed the nanowire tips from the backside of the AAO template
(Figure S1, below). The detailed steps for obtaining this image have been described in our
previous work1. Briefly, the nanopores were filled with rubrene using a centrifugation assisted
organic nanowire growth technique1 and the top surface of the template was coated with a
sacrificial organic. Next, the aluminum substrate was etched away in a saturated mercuric
chloride solution. Finally, the barrier layer at the back surface of the template is etched slightly
in 5% phosphoric acid to expose the nanowire tips. As seen from Figure S1, the tips have been
exposed over large area, which confirms uniform filling even at the pore bottom.
Figure S1. Rubrene nanowire tips exposed from the backside of the AAO template.
II. Coercive field of Cobalt (Co) nanowires.
The coercive field of Co nanowires decreases with increasing temperature. Figure S2 shows the
temperature dependence of the coercive field of Co nanowires as determined from the
magnetoresistance measurements (Figure 2, main text). Previous studies on transition metal
nanowires have demonstrated a linear decrease of coercivity with temperature2. The extrapolation
from Figure S2 yields a
Figure S2. Coercive field of Co nanowire as a function of temperature.
coercive field value of 689 G at 295K. We have performed vibrating sample magnetometer (VSM)
measurements at room temperature on Co nanowires (embedded in AAO) of similar geometry as in
the actual spin valve device. From this measurement we obtain a coercive field value of 680 G
(Figure S3), which is in good agreement with the extrapolated value obtained from Figure S2.
Figure S3. Room temperature magnetization curve of Co nanowires embedded in AAO. The Co
nanowires have same dimensions as the Co contacts in actual spin valve devices.
III. Coercive field of Nickel (Ni) thin film.
We have performed room temperature VSM (Vibrating Sample Magnetometry) measurement on Ni
thin film (Figure S4). The coercive field in this plot is ~ 170 G, which is slightly smaller than the
low-temperature coercive field values (~ 180 G) obtained from the magnetoresistance
measurements (Figure 2, main article). We note that compared to Co nanowires, the coercive field
of top e-beam evaporated Ni thin film has very weak dependence on temperature.
Figure S4. Room temperature magnetization curve of electron-beam evaporated Ni thin film.
1
K. Alam, A.P. Singh, R. Starko-Bowes, S.C. Bodepudi, and S. Pramanik, Advanced Functional
Materials 22, 3298 (2012).
2
J. Sarkar, G. Khan, and A. Basumallick, Bulletin of Materials Science 30, 271 (2007).