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Description:
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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 . |