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 * 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, ID2 Department of Chemistry, University of Idaho, Moscow, ID

Result and DiscussionGoal: 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.

0.00E+00 5.00E-01 1.00E+00 1.50E+000.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

f(x) = 0.0026189918 x − 0.00043022555

591 G

Voltage (V)

Curr

ent (

A)

0.00E

+00

2.00E

-01

4.00E

-01

6.00E

-01

8.00E

-01

1.00E

+00

1.20E

+000.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

f(x) = 0.00263919085 x − 0.00052109068

0 G

Voltage (V)

Curr

ent (

A)

0.00E

+00

2.00E

-01

4.00E

-01

6.00E

-01

8.00E

-01

1.00E

+00

1.20E

+000.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

f(x) = 0.00261003705 x − 0.00039038779

1048 G

Voltage (V)

Curr

ent (

A)

0.00E+00 5.00E-01 1.00E+00 1.50E+000.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

f(x) = 0.00262880285 x − 0.00031419605

2404 G

Voltage (V)

Curr

ent (

A)

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 pathwaysO magnetic field induced switching on of conductive pathways

X

XO

O

+V

-V

Schematic representation of random electrical junctions in a random arrayof 1-D nanostructures in the presence of magnetic fields

ACKNOWLEDGEMENTS• Ranger Adams for programming

support

0 500 1000 1500 2000 2500 3000 3500 4000322

323

324

325

326

327

328

329

Resistance

Magnetic Field (G)

Resis

tanc

e (o

hm)

0 500 1000 1500 2000 2500 3000 3500 4000352

354

356

358

360

362

364

366

Resistance

Magnetic Field (G)

Resis

tanc

e (o

hms)

0.00E+00 5.00E-01 1.00E+00

-5.00E-04

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

3.00E-030 G370 G751 G1134 G1516 G1895 G2271 G2638 G2970 G3250 G3480 G

Voltage (V)

Curr

ent (

A)