1. SEM Morphology
• A SEM micrograph of the GUITAR covered
nanosprings is shown in figure 1.
• For coating GUITAR two different method
used, (b,d) at 700℃ without N2
• (a,c) at 800 ℃ under N2 purge
• The diameter of carbon coated on nanosprings
is almost 800 nm.
• The length of the nanosprings is about 1-2 mm.
We report on the initial studies of the
manifestation of magnetoresistance of a
3D network of intertwined 1D
nanostructures – nanosprings. The
network consists of silica nanosprings
coated with a conductive carbon coating
(Graphitic University of Idaho from Tar
–GUITAR), both of which were
developed at the University of Idaho.
The nanosprings are initially grown on a
quartz substrate and subsequently
coated with GUITAR.
Goal
• Investigate the morphology of
nanosprings coated with GUITAR
• The effect of the conductive pathway
in magnetoresistance in 3D network
• The influence of the magnetic field
on the current.
• The relationship between magnetic
field and resistance
Sample Preparation
• The nanosprings samples were produced in a
custom built CVD system. The nanosprings were
grown on a quartz substrate.
• The GUITAR deposition was carried out in a tube
furnace for one hour at 800 oC.
Background
• Magnetoresistance material has high magnetic and
electrical properties; therefore it has great potential
as next generation magnetic field sensing devices.
• The magnetoresistance effect depends on both the
strength of the magnetic field and the relative
direction of the magnetic field with respect to the
current, where changes the resistance with applied
various magnetic field.
• The signal response of a device, or material, is
often characterized by the percentage
magnetoresistance, the variation of resistance (R)
of a material as a function of an external magnetic
field (B) described by: R=F(B)
• where ∆R is the change in resistance in an applied
field and R is the resistance in the absence of an
applied field MR=
ΔR
𝑅
* 100%
• The stochastic nature of the conductive pathways
will manifest in magnetoresistance
ABSTRACT
Experimental Design
• (I1) the current was measured two
electrical probes with a one-
centimeter separation.
• The magnetic field was applied
perpendicular to the plane
containing the two electrodes.
• By applying and increasing
magnetic field through the
nanosprings sample, (I2) is
changing.
• Data was obtained for applied
voltages from 0-1 V.
Magnetoresistance in a 3D network of 1D nanostructure
Negar Rajabi1, Cassandra Clark1, Peter Wojcik1, Frank Cheng2, and David McIlroy1
1 Department of Physics, University of Idaho, Moscow, ID
2 Department of Chemistry, University of Idaho, Moscow, ID
Result and Discussion
Goal: Show the relationship between resistance
and magnetic field
• The effect of magnetic fields on resistance
• Applying a magnetic field can increase the
resistance of a material, since the magnetic
force on the moving change will tend to
increase the number of collisions between
charges.
• Figure 2 and 3, the resistance is fluctuated
because of the fact that as the magnetic field is
changing the current is changing its route
through the nanosprings in the sample.
• The magnetoresistance of the 3D Guitar-
nanosprings network was measured at field
strengths from 0-300 G, where the current was
measured two electrical probes with a one
centimeter separation.
• The magnetoresistance exhibited semi-chaotic
changes as a function of magnetic field strength
and has been attributed to magnetic-induced
random transition of new current pathways
with the lowest resistance.
• the overall trend of the magnetoresistance
increased with field strength and reached a
maximum of 3% at 3000 G.
Current-Voltage
Characteristics
• The influence of the external magnetic
field on the current voltage (I-V)
characteristic shown in figure 4.
• The current increases along with the
increase in the voltage.
• (I-V) linear graph is obtained when
magnetic field is perpendicular to I.
• No obvious conductance change is
observed with various magnetic fields.
• The resistance calculated from Ohm’s
Law by R = V / I
• According to the figures, the resistance
is around 2×10^(-3) Ohm from 0-1 V
Conclusions and Future Work
• A 3D network of conductive nanosprings
exhibits negative and positive
magnetoresistance. Note, Au thin films were
used as controls and did not exhibit
magnetoresistance for the magnetic field
strengths used in this study.
• The I-V curves exhibit excellent linearity, i.e.
resistance, for a constant magnetic field, which
eliminates the possibility that conduction
channels are being permanently broken. It also
demonstrates that the magnetoresistance is
independent of the driving current.
• The magnetoresistance is attributed to the 3D
morphology of the nanospring network, where
the magnetic field can open and close
conductive pathways via the Lorentz force.
• The magnetoresistance can likely be enhanced
by constricting the dimensions of the network.
• Sample sizes will be reduced to gradually
narrower strips to minimized the possible
current pathways.
y = 0.0026190x - 0.0004302
0.00E+00
5.00E-04
1.00E-03
1.50E-03
2.00E-03
2.50E-03
0.00E+00 2.00E-01 4.00E-01 6.00E-01 8.00E-01 1.00E+001.20E+00
Current(A)
Voltage (V)
591 G
y = 0.0026392x - 0.0005211
0.00E+00
5.00E-04
1.00E-03
1.50E-03
2.00E-03
2.50E-03
0.00E+00 2.00E-01 4.00E-01 6.00E-01 8.00E-01 1.00E+00 1.20E+00
Current(A)
Voltage (V)
0 G
y = 0.0026100x - 0.0003904
0.00E+00
5.00E-04
1.00E-03
1.50E-03
2.00E-03
2.50E-03
0.00E+00 2.00E-01 4.00E-01 6.00E-01 8.00E-01 1.00E+00 1.20E+00
Current(A)
Voltage (V)
1048 G
y = 0.0026288x - 0.0003142
0.00E+00
5.00E-04
1.00E-03
1.50E-03
2.00E-03
2.50E-03
0.00E+002.00E-01 4.00E-01 6.00E-01 8.00E-011.00E+001.20E+00
Current(A)
Voltage (V)
2404 G
The diameter of GUITAR coated nanosprings are (a)
1-2μm, (b) ~1 mm, (c) ~800 nm and (d) > 2mm.
a b
c d
X magnetic field induced switching off of conductive pathways
O magnetic field induced switching on of conductive pathways
X
X
O
O
+V
-V
Schematic representation of random electrical junctions in a random array
of 1-D nanostructures in the presence of magnetic fields
ACKNOWLEDGEMENTS
• Ranger Adams for programming
support
323.5
324
324.5
325
325.5
326
326.5
327
327.5
328
328.5
0 500 1000 1500 2000 2500 3000 3500 4000
Resistance(ohm)
Magnetic Field (G)
Resistance
356
357
358
359
360
361
362
363
364
365
0 500 1000 1500 2000 2500 3000 3500 4000
Resistance(ohms)
Magnetic Field (G)
Resistance
-5.00E-04
0.00E+00
5.00E-04
1.00E-03
1.50E-03
2.00E-03
2.50E-03
3.00E-03
0.00E+00 2.00E-01 4.00E-01 6.00E-01 8.00E-01 1.00E+00
Current(A)
Voltage (V)
0 G
370 G
751 G
1134 G
1516 G
1895 G
2271 G
2638 G
2970 G
3250 G
3480 G