This dissertation focuses on three separate studies. First, magnetization of the Mn12-
acetate was studied by low temperature hysteresis loops and DC magnetization data on
magnetically aligned Mn12-acetate micro-crystals. Secondly, Mn12-acetate thin films
were fabricated and characterized by AFM and STM. Finally, magnetization of the film
material was also studied.
Enhanced alignment of Mn12-acetate micro-crystals as compared to prior studies was
verified by observation of several sharp steps in low temperature hysteresis loops. It was
found that ~ 0.5 T is sufficient to orient the micro-crystals in an organic solvent to a
degree comparable to a single crystal. The degree of the alignment was controlled by
varying the magnetic field at room temperature and during the cooling process.
Subsequently, low temperature hysteresis loops and DC magnetizations were measured
for each prepared orientation state of a sample. The high temperature magnetic
anisotropy responsible for the alignment could not be measured, possibly due to its small
magnitude. Mn12-acetate was deposited onto Si/SiO2 by a solution evaporation method. Atomic
force microscopy studies revealed that 2 nm thick films of molecular level smoothness
were formed. Mn12-acetate was also deposited onto a Highly Ordered Pyrolytic Graphite
(HOPG) surface for scanning tunneling microscopy (STM) studies. A self-assembled
triangular lattice was observed in the Mn12-acetate thin films by STM at room
temperature under ambient conditions. These STM images show typical center to center
intermolecular separations of about 6.3 nm and height corrugation of less than 0.5 nm.
Magnetization measurements were not successful in Mn12-acetate thin films due to
the small amount of material in the film and the large background signal from the
substrate. Therefore, a sample for the magnetization measurements, called “film
material”, was made by evaporating a dilute solution of Mn12-acetate powder in
acetonitrile. Significant changes in magnetic properties of the film material were
observed from magnetization measurements. The blocking temperature of the film
material was found to increase to TB > 10 K at low magnetic fields.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2574 |
| Date | 15 May 2009 |
| Creators | Seo, Dongmin |
| Contributors | Teizer, Winfried |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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