Spin Dependent Transport Properties of Magnetic Nanostructures

1. Spin Dependent Transport Properties of Magnetic Nanostructures Amédée d’Aboville, with Dr. J. Philip, Dr. S. Kang, J. Battogtokh

2. Outline • Introduction to Nanostructures • Magnetic Nanostructures • Growth • Properties • Device fabrication • Device characterization

3. What is Nano? • SI unit of length = 1m • Other units are the millimeter: 1x 10-3 m micrometer : 1 x 10-6 m nanometer : 1 x 10-9 m 1 meter = 1 billion nanometers • The width of a hair is about 50 000 nm • Nanostructures have at least one dimension less than 100nm

4. What is Nanotechnology? • Nanotechnology is the manipulation, fabrication, and characterization of nanostructures

5. What are the Applications of Nanotechnology? • Better food packaging • Stronger, lighter materials • Optical Computing • Better Displays • Sunscreen • Quantum Computing • Spin-dependent electronics

6. Galfenol • Galfenol is a Gallium Iron compound with a specific stoichiometric composition (Ga0.2Fe0.8) • Galfenol is ferromagnetic, and has a Curie Temperature of 1000 K • There are also a range of interesting properties (ie. Magnetostriction).

7. Nanowire Growth: Electro-Spinning • A syringe is filled with a solution of correct stochiometric compositions • A high potential is applied between the tip of the needle and the collector • Nanowires spin out of the syringe

9. Optical Microscope picture of Electro-spun GaFe NW mm

10. Sample Preparation: Sonication • Nanowires are separated from the substrate by placing in an ultrasonic bath • The Nanowires are left in an IPA solution

11. Preparation • Coordinates of the NW are obtained using an SEM • Electrodes designed are designed using a Computer Aided Design program • The CAD file is fed into a computer • The computer controls a finely focused electron beam

12. Lithography • A sample is coated with electron sensitive resist material, similar to photographic film • A computer controlled Electron Beam exposes certain parts of the resist • The exposed sections change molecular weight and can be dissolved in a particular solvent Resist Nanowire Si Wafer

13. Ultra-High Vacuum Deposition • State of the art technique to deposit high quality material • High vacuum can be achieved ( up to 10-10 torr) • Ti and Cu electrodes are deposited in thin sheets ( 5nm and 100nm, respectively)

14. Metallization and liftoff • Electrodes are deposited with the Ultra High Vacuum Deposition system • The sheet of resist is removed with acetone, leaving only the metal in the exposed parts Resist Nanowire Si Wafer

15. Galfenol Nanowire with Ti and Cu electrodes(500x)

16. Spin Dependent Transport Properties • Placing Galfenol NW in an external field can orient its electron spin in the desired direction • The NW resistance changes with the orientation of its electrons relative to the current

17. Property Measurements • We apply a voltage and measure the resultant drain to source current Nanowire acts as a channel Drain Source Wafer acts as gate

18. Expected Results • There is a thin sheet of oxide on top of the nanowire which acts as an insulator • The electrons get through the sheet by quantum tunneling • The oxide is a Quantum Tunneling Barrier GaFe Oxide Drain Source Nanowire Wafer

19. Measured properties

20. Conclusion • We have grown Galfenol NW • Analyzed their structure • Built devices out of single NWs • Measured these device properties • Analyzed these device measurements