Dr. Takele
Seda
Western Washington University - Department of Physics
Western Washington University - Department of Physics
Magntic-electronic
properties of iron oxides and hydroxides
1. Nano-magnetic materials produced by mechanochemical reaction of metals/metal oxides with hematite-Fe2O3.
2. Nano-ferrihydrites synthesiszed by different chemical routes
Facilities
The geology department has given us access to their x-ray diffractometer and vibrating sample magnetometer.
Iron is an element
of prime importance in the form of ferric and ferrous oxide/hydroxide
nanoparticles in
natural systems and technological applications.
Because, many iron
oxides are
magnetically ordered above 300K and can retain memory for millions of years, they constitute a unique archive of the history of their source, hence that of their environment.
Nanophase particles can be thermally unstable, hence their magnetic properties at low, high and ambient temperatures are clearly different. Because of such size-dependent properties,
these nanophase particles have influential roles in identifying environmental processes as they do in modern nanoscale technologies, as a result of the increasing role of the surface electron
spins with decreasing particle size.
magnetically ordered above 300K and can retain memory for millions of years, they constitute a unique archive of the history of their source, hence that of their environment.
Nanophase particles can be thermally unstable, hence their magnetic properties at low, high and ambient temperatures are clearly different. Because of such size-dependent properties,
these nanophase particles have influential roles in identifying environmental processes as they do in modern nanoscale technologies, as a result of the increasing role of the surface electron
spins with decreasing particle size.
Therefore,
it is of fundamental importance to understand the magnetic-electronic
properties of these materials and and their transformations from one
form to another on synthetic and
natural equivalent materials. Our current research is, therefore, focussed on the following projects.
natural equivalent materials. Our current research is, therefore, focussed on the following projects.
1. Nano-magnetic materials produced by mechanochemical reaction of metals/metal oxides with hematite-Fe2O3.
2. Nano-ferrihydrites synthesiszed by different chemical routes
Facilities
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The
physics department at Western Washington
University uses
a SPEX 8000 vibrating ball mill for mechanochemical reaction of
powders. Several vials can be chosen from depending on
application. A tungsten carbide vial as well as a zirconia
ceramic vial are currently on hand for wet or dry grinding/mixing. The mill is housed in a soft plastic glove box which holds an inert gas atmosphere with refrigeration. |
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Control
electronics and data acquision system for 57Fe
Mössbauer spectroscopy.
All the Mossbauer facilities used in our lab are equiped with drive
systems and control electronics from Wissel instruments (Germany) and
Canberra instruments. |
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Variable low temperature (300 - 5K ) 57Fe Mössbauer uses a closed cycle He-refrigerator from Janis company. The facility is crucial for determining the magnetic ordering temperatures of bulk materials below room temperature and identing phase compositions where spectral overlap makes the analysis at room temperature defficult. For nanophase materials, it is used to determine the blocking temperatures. |
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Variable high temp Mössbauer (300 -1300K). Most naturally occuring iron oxides have magnetic ordering temperatures (Niel for antiferromagnetic and curie for ferro/ferrimagnetic) above room temperature. Determining such ordering temperature requires Mossbauer measurements at higher temperatures. Also some natural minerals are compossed of different magnetic phases with overlapping Mossbauer spectra at room temperature. Separation of such phases is easier at higher temperatures as they have different magnetic ordering temperatures. |
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Conversion
electron Mössbauer (Room Temp): The most used
Mossbauer technique is the transmission geometry, where the spectrum is
recorded of the transmitted gamma-ray as a function of drive velocity.
The secondary radiactive process can be utilized for surface
investigations, in which the information depth depends on the nature of
the redorded radiation. The nuclear relaxation occurs by internal
conversion, which results in a cascade of different raduiations. These
re-imitted radiations include gamma-rays, x-rays or electrons.
A specially designed continous gas flow detector is required for the
detection of these radiations. In our lab we have a Rikon-5 dector
from Wissel that works for the detection of conversion electrons,
x-rays and gamma-ray by simply changes the mixture of the gas at room
temperature as the three radiations have diffent penetration depths in
materials.
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Scientific Technical services (SciTech), a service paid for by student tuition, grants use of their Vega TS-5136MM scanning electron microscope. |
The geology department has given us access to their x-ray diffractometer and vibrating sample magnetometer.