SYNTHESIS OF IRON-GERMANIUM

Summer Research 2010Rohan Isaac Berea CollegeAdvisor: Dr. Amer Lahamer

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.

Tests

X-ray diffraction

Mössbauer spectroscopy

Vibrating Sample Magnetometer

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.

Mössbauer spectrometer

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.

Vibrating Sample Magnetometer

Compounds to synthesize

Fe1-xCoxZWhere Z is Si, Ge or Sn

Samples made

Fe0.8Co0.2Si

Fe1.4Ge

Fe1.67Ge

FeGe2

FeGe

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

Fe0.8Co0.2Si

Position [°2Theta]

20 30 40 50 60 70 80

Counts

0

500

1000

1500

rohan1.rd

Fe0.8Co0.2Si

Position [°2Theta]

20 30 40 50 60 70 80

Counts

0

1000

2000

rohan2.rd

After Annealing

Fe0.8Co0.2Si

Position [°2Theta]

20 30 40 50 60 70 80

Peak List

86-0794

38-1397

Fe1.4Ge

Cooked 850°C for 6 hours

Annealed at 950°C for 6 hours

X-ray revealed Fe1.4Ge

Fe1.4Ge: x-ray

`

Position [°2Theta]

20 30 40 50 60 70 80

Counts

0

500

1000

1500

rohan4.rd

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)

Fe1.4Ge

`

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

Fe1.67Ge

Position [°2Theta]

20 30 40 50 60 70 80

Counts

0

1000

2000

rohan8.rd

Fe1.67Ge

FeGe2

Cook for 1 day hours at 700°C

X-ray found FeGe2 and Fe2Ge

FeGe2

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

°

FeGe

Position [°2Theta]

20 30 40 50 60 70 80

Counts

0

500

1000

1500

rohan10.rd

FeGe

Position [°2Theta]

20 30 40 50 60 70 80

Peak List

17-0228

FeGe

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.