Fe/Bi Te /Fe Tunneling ₂ ₃Magneto-Resistance with topological insulator barrierVallery Salomon and Dereje Seifu, Department of Physics, Morgan State University, Baltimore, MD 21251

ABSTRACTThin film tri-layer structure Fe/Bi2Te3/Fe was synthesized using magnetron DC / RF sputtering. This sample was synthesized at a substrate temperature of 100C. It was studied using in-house built magneto-optic Kerr effect (MOKE) instrument. The operating principles of MOKE consist of measuring changes in polarization of light reflected from a magnetic sample. The bulk magnetization was measured using vibrating sample magnetometer (VSM). Tunnel magneto-resistance (TMR) effect occurs in a structure that is composed of two conductors separated by a thin insulator of the order of few nanometers, the insulator barrier in this case is a well known topological insulator, Bi2Te3. In this structure, electrons tunnel from one of the conductors to the other through the insulating barrier. This is a forbidden process in classical physics, tunnel magneto-resistance is a purely quantum mechanical effect which is key in developing magnetoresistive random access memory (MRAM), magnetic sensors, and novel logic devices.

Sample Synthesis• A DC / RF magnetron sputtering system was used to synthesize

multi-layered thin film of Fe/Bi2/Te3/Fe on MgO(100).• Fe films with thickness 50 nm were deposited at 100 degrees• A 5 nm layer of Bi2/Te3 was deposited at RT.

Magneto-Optic Kerr Effect (MOKE) Schematic

Electronic Component of MOKE1.Computer display of hysteresis

loop during measurement.

2.PEM-100 Controller-photo elastic modulator (PEM) modulates the polarization of the laser light passing through the PEM optical head by50kH

3. SRS Preamplifier-converts current signal from the photo diode to voltage Signal and feeds it to the Lock-in-Amplifier

4.SRS Lock-in amplifier (LIA) – is used to increase signal to noise ratio

5.BOP Power supply-Supplies current to the electromagnet in response to a signal from LIA’s auxiliary output.

6.Computer system interfaced with electronic parts of MOKE.

Optical Part of MOKEWavelength and 5mW output power

8. Polarizer-linearly polarize light and allows linearly polarized light at 45 from the vertical to pass through

2b. PEM Optical head-modulates the polarization of the laser light passing through. It is connected to the lock-in amplifier reference input so only the modulated light forms the signal.

9. Electromagnet-The sample is placed in a varying magnetic field at the center of the electromagnet

10. Sample holder-used to hold the sample in place and rotates in a plane perpendicular to the direction of the light

11. Analyzer-crossed with the polarizer minimizing light passing through it so that to only let through the part of light whose polarization is rotated due to reflection from a ferromagnetic sample in an external magnetic field.

12. Photo diode- collects light waves and converts it to a current signal which is fed to the pre-amplifier, which then converts the current signal to a voltage signal which is then fed to the Lock-in amplifier

MOKE

MOKE (Azimuthal Plot)

100

200

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90

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180 0

MOKE Angle vs Hc

Angle

Hc

Hc (Oe) vs Angle using MOKE

0 50 100 150 200 250 300 350 400255

260

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285

Angle vs Hc (Oe)

Angle

Hc (O

e)

VSM of Fe/Bi2Te3/Fe on MgO(100) grown at T=100C

-1.50E+03 -1.00E+03 -5.00E+02 0.00E+00 5.00E+02 1.00E+03 1.50E+03

-0.0025

-0.002

-0.0015

-0.001

-0.0005

0

0.0005

0.001

0.0015

0.002

0.0025

90 Degrees45 Degrees0 Degrees

Applied Field (Oe)

Mag

netiz

ation

(em

u)

Hysteresis at Various Low Temperature Measurements

-2.00E+03 -1.50E+03 -1.00E+03 -5.00E+02 0.00E+00 5.00E+02 1.00E+03 1.50E+03 2.00E+03

-2.50E-03

-2.00E-03

-1.50E-03

-1.00E-03

-5.00E-04

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

-192.16 C-153.41-93.33 C300k

Hc (Oe)

M (e

mu)

Variation of Hc, Ms, & Mr using VSM

0 10 20 30 40 50 60 70 80 90 1000

50

100

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0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

Hc(Oe)Ms(emu)Mr(emu)

Angle

Hc (O

e)

Conclusion• From VSM data, at 45 degrees the coercive field was

maximum, at value 243.9 Oe.• The Mr and Ms values were maximum at 0 degrees.• The Azimuthal graph of MOKE shows that the material does

not have substantial anisotropy.• In MOKE the difference between the maximum and minimum

Hc values is 15 Oe, measured using longitudinal MOKE.• The difference between the surface coercive field measured

using MOKE and bulk coercive field measure using MOKE is found to be 38 Oe.

• In the near future AFM / MFM and MR measurements will be performed on this system.

Acknowledgements

We would like to acknowledge support by ARL W911NF-12-2-0041 and

by NSF MRI -DMR-1337339.

Thank you