Summer Research 2010 Rohan Isaac Berea College Advisor…isaacro/research/Synthesis_of_Iron... ·...
Transcript of Summer Research 2010 Rohan Isaac Berea College Advisor…isaacro/research/Synthesis_of_Iron... ·...
What are half-metals?
Half metals are substances that act as a conductor to electrons of one spin while acting as a insulator to those with opposite spin.
Conduction electrons are 100% spin polarized
Application
In the emerging field of spintronics.
Use the spin of electrons along with the associated magnetic moment in solid state devices.
Can create completely spin polarized current.
Synthesis
Mix stoichiometric mixture of required materials till it becomes homogenous .
Heat it or ‘cook’ it at high temperature.
Under vacuum or flow of argon (inert gas) so that materials only react with each other and not with the air or any other materials.
Synthesis under vacuum
Place pulverized mixture in thin quartz tube.
Evacuate using strong vacuum pump
Seal by melting end with oxy-acetylene torch
Heat tube in a box furnace to desired temperature
Synthesis under argon flow
Place mixture in silica boat.
Place boat in the center of tube in tube furnace.
Connect one end of tube to argon source and the other to a gas bubbler and then to hood.
Start flow of argon till tube is full.
Turn on the furnace and heat substance.
Annealing
After cooking process, substances are rarely pure or uniform.
They contain multiple phases of the compound required.
So we re-pulverize the substance made and heat it above its recrystallization temperature for a longer period of time to purify it and make it homogenous.
X-ray diffraction
Beam of x-ray hits the material and diffracts into a number of specific directions
This diffraction is due to the crystal structure of the material and is like a unique fingerprint for each material
We can compare these results with a database of previously known crystals so we can find out what substance we have made.
Mössbauer spectroscopy
Use the radioactive decay of a cobalt (57Co) source(half-life of 271.74 days) to produce gamma rays.
The absorption graph of the material will show us the magnetic properties of the material.
A sextet will indicate a ferromagnetic substance while a doublet will indicate a diamagnetic one.
Vibrating Sample Magnetometer (VSM)
A magnetometer is a scientific instrument used to measure the strength and/or direction of a magnetic field.
We use the VSM in measuring magnetization versus temperature of the samples in search of critical temperatures.
Fe0.8Co0.2Si
Cooked it at 1100°C for 2 hours
Annealed it for 4 hours at 860°C
X-ray diffraction on result – not a clean graph – needed to anneal more
Annealed for 3 ½ hours at 1000°C
X-ray diffraction again – clean graph
Fe1.4Ge
`
6543210-1-2-3-4-5-6v (mm/s)
0.1
21
0.1
20
0.1
19
0.1
18
0.1
17
0.1
16
Inte
nsity (
10
6 c
ts)
Fe1.67Ge
Cooked for 1 day at 850°C
X-ray found Fe1.4Ge
Annealed at 950°C for 1 days.
X-ray found Fe1.4Ge
Annealed at 950°C for 2.5 day.
X-ray found Fe1.67Ge
FeGe
Attempt to balance the escape of a percentage of germanium by starting initially with more germanium than necessary, and anticipating that the same percent of germanium will escape under the same conditions.
Cook for 6 hours at 850°C
Anneal for 6 hours at 950°C
Other ideas
Making pellets of the mixtures
Overcompensating for one element
Attempting to synthesize FeSi0.5Ge0.5
Fe0.8Co0.2Ge and FeSn
Cooked and annealed at a range of temperatures between 400°C and 700°C
Conclusion
Successfully replicated creating half metal Fe0.8Co0.2Si
Multiple phases of FeGe
Heat treatment critical in determining phase
Difficult to obtain a stable sample of FeGe
Acknowledgements
Dr. Amer Lahamer - for his help and guidance through the entire summer of research.
Tommy Boykin and Tyler Vanover - students with who I worked over the summer and who helped make this a very pleasant experience.
URCPP program at Berea College, without whose funding none of this would be possible.
Dan Brewer for his technical help in the lab and Alice Hooker for assistance in gathering supplies.