Supplementary Information
In this Supplementary Information section we show in more detail the spin-valve giant
magnetoresistance (GMR) measurements on devices with a variety of organic
semiconductor (OSE) spacer thicknesses, in addition to those shown in Fig. 2a. We also
show a number of magnetoresistance (MR) measurements on several devices that were
fabricated specifically for the purpose of serving for control measurements in comparison
with the real spin-valve devices.
(1) GMR in various LSMO/Alq3/Co spin-valve devices
We have sequentially fabricated LSMO/Alq3/Co devices with various OSE spacer
thicknesses using the same LSMO piece, in order to get reliable results of the dependence
of the GMR value on the spacer thickness, d. For each new d we washed the LSMO thin
film from the previous device and reused it to evaporate the OSE spacer and Co electrode
for the new device. In this way a series of spin-valve devices with different d, which were
fabricated under the same conditions, and on the same bottom LSMO electrode, were
measured at 11 K. The GMR hysteresis curves (shown in Fig. S1) were taken with low
bias voltages where the GMR is maximized; the maximum obtained GMR values are
summarized in Fig. 2b in the text.
(2) I(V) and EL(V) responses of an ITO/Alq3/Co control device
To check whether the transport in spin-valve devices is dominated by pinholes, we have
fabricated a control device where the opaque LSMO bottom electrode was replaced by
the transparent ITO electrode, which is non-magnetic. The control device was fabricated
under the same conditions as the spin-valve devices, having an OSE spacer thickness d =
160 nm. The obtained I(V) response at low V was similar to that shown in Fig. 1d, and
the current is probably due to the hole injection from the ITO bottom electrode. The I(V)
response at high forward bias voltage V of up to 30 volt is shown in Fig. S2 inset. It has a
threshold voltage at about 26 V, where electrons are also injected into the OSE from the
top Co electrode. The threshold bias voltage for electron injection is higher than that for
hole injection due to the higher energy barrier for electron injection (see Fig. 1c). The
hole and electron injection into the OSE spacer can be inferred from the obtained
electroluminescence (EL) that was emitted at high applied bias voltage (Fig. S2). The
EL(V) response is very similar to the I(V) response, as shown in Fig. S2 inset; whereas
the external quantum efficiency shows saturation at a current, I  0.5 mA.
These results obtained on a control device prove that the transport in the fabricated
LSMO/Alq3/Co spin-valve devices is not dominated by pinholes under Co evaporation.
They also show that in principle both electrons and holes may be injected into the OSE
layer from the LSMO and Co electrodes at high bias voltages. Similar measurements on
organic light emitting devices involving LSMO as an anode were recently completed by
the Bologna groupS1. We note, however that a thicker evaporated Co layer destroys the
device I(V) response and leads to lack of EL emission.
In addition we also measured conductivity-detected magnetic resonance on the ITO
control device. As shown in Fig. S3, we obtain a spin ½ resonance at g  2. This shows
that spin ½ carriers are indeed injected into the OSE spacer, consistent with the
conclusion inferred above from the existence of EL emission in the device.
(3) MR measurements on control devices
To prove that the GMR response observed in LSMO/Alq3/Co devices originates from the
spin-valve effect rather than the metal electrodes or the OSE spacer itself, we prepared
several control devices and measured their MR response vs. the magnetic field, H.
We first measured the low temperature MR response of the bare metal films used for
fabricating the FM spin-valve device electrodes, namely Co (Fig. S4) and LSMO (Fig.
S5). As seen in Fig. S4 the MR response of a Co film is very low, of about 0.5%
measured with a signal to noise ratio of 1:1. This low signal originates from the
extremely low resistance of the Co film, which is about six orders of magnitude smaller
than the resistance of the spin-valve devices used in this work. The MR of LSMO is
relatively better-resolved (Fig. S5) but is still within 0.5% in the same small field range
as that in the spin-valve devices; also its resistance is about three orders of magnitude
smaller than that of the spin-valve devices. We also note that the MR responses of both
electrodes do not show measurable hysteresis with H, which is the characteristic
signature of a spin-valve device.
Next we checked the MR response of an ITO/Alq3/Co control device to check whether
the obtained GMR in the spin-valve devices originates from the OSE spacer itself. These
measurements are shown in Fig. S6. Again the MR response is very small, within a
fraction of 1 %, and in addition it does not show any hysteresis with H.
We therefore conclude that the spin-valve response obtained in our LSMO/Alq3/Co
devices originates from the device configuration itself, involving spin injecting and
transport in the OSE spacer, as is concluded in the text.
(4) ITO/parylene/Co control device
The final control device that we have fabricated and studied was an ITO/parylene/Co
device having a spacer thickness of 150 nm. Parylene is used for the insulating layer in
organic field effect transistorsS2 and thus its MR response is important to measure. If the
obtained spin-valve effect in LSMO/Alq3/Co devices were due to Co inclusion and
electron tunneling to the LSMO opposite electrode without involving the OSE spacer at
all, then similar effect would have to be measured with this control device, since the
pinholes and Co inclusions should also be present in this control devices to show similar
transport behaviors.
Fig. S7 shows the I(V) measurement on the ITO/parylene/Co control device. The
parylene film thickness is 150 nm. The Co layer is about 5 nm thick and shows welldefined hysteresis. However, the resistance of the device is over 60 Gs, many orders of
magnitude greater than that in the ITO/Alq3/Co or LSMO/Alq3/Co devices with similar
spacer thickness. This results shows that the transport properties of the LSMO/Alq3/Co
devices are not caused by Co inclusions or pinholes.
Figure Captions:
Fig. S1: GMR of LSMO/ Alq3/Co spin-valve devices of various spacer thicknesses, d,
measured at 11 K.
Fig. S2: Room temperature external quantum efficiency of a control light-emitting
ITO/Alq3/Co device with d = 160 nm. Both current-voltage, I(V), and
electroluminescence intensity, EL(V), responses of this device are shown in the
inset.
Fig. S3: The spin ½ resonance measured using the conductivity-detected magnetic
resonance technique on a control ITO/Alq3/Co device. A relatively strong
resonance at g  2 shows that spin ½ carriers are indeed injected into the OSE
spacer.
Fig. S4: The MR response of the bare Co electrode measured at bias voltage of 0.1 mV
and 11 K.
Fig. S5: The MR response of the bare LSMO electrode measured at bias voltage of 5 mV
and 11 K.
Fig. S6: The MR response of a control device ITO/Alq3/Co measured at bias voltage of
10 mV and 11 K.
Fig. S7: The I(V) of the ITO/parylene/ Co device measured at room temperature.
References
S1: Arisi, E. et al. Organic light emitting diodes with spin polarized electrodes. J. Appl.
Phys. 93, 7682-7683 (2003).
S2: Podzorov, V. et al. Field-effect transistors on rubrene single crystals with parylene
gate insulator. Appl. Phys. Lett. 82, 1739-1741 (2003).