Richard Feynman is the
inspiration behind the new burgeoning field of Nanotechnology. In a
historic talk "There is plenty of room at
the bottom..." at Caltech in 1959, he challenged scientists to enter a new
field of physics that he predicted will be the answer to future technological
needs. The transcript of his talk is available at this link .
Feynman's visions and dreams have just started becoming reality in the past
few years....
Nanotechnology has opened up exciting possibilities where one can think of
manipulating the basic properties of materials. For example, in magnetic
materials, fundamental properties like the coercivity,
saturation magnetization etc. can be tailored in engineered nanostructured
materials by controlling the grain size to be in the 10 to 100 nm range.
We are investigating the magnetic and electromagnetic response in a number of nanostructured materials and thin films. Our goals are to better understand the structure-property correlation, magnetism, novel electronic phenomena and the high-frequency properties. We use a suite of electrical and magnetic measurements in our laboratory to probe these important issues. These studies could lead to application of these novel materials in advanced electromagnetic and so-called “spintronic” devices. We have active collaborations with research groups at USF and several other academic/industrial labs all over the world.
Research nuggets from the Materials Physics group @ USF: [Oct 2005]
·
DC and AC
magnetization, resistivity and magnetotransport
in bulk, thin film, single crystals and nanostructured
materials are routinely studied in our lab using a commercial Physical Property
Measurement System (PPMS) from Quantum Design with a temperature range of 2
– 300K and field range 0 – 7 Tesla.
·
In addition to
the measurement capabilities of the commercial PPMS, we have developed
home-made experimental set-ups that have been integrated with the PPMS:
o
RF susceptibility
in magnetic materials
o
Point contact Andreev Reflection and Tunneling spectroscopy
These experiments have yielded numerous results that
have been presented at conferences and also published in peer-reviewed
journals. Our unique experimental capabilities have continued to attract
several research collaborators who provide novel materials for our research.
·
A signature
experiment pioneered in our lab is measuring the transverse susceptibility over
a wide range in field and temperature using a novel RF resonant technique based
on a tunnel-diode oscillator. Over the past few years, we have published over 40
papers and demonstrated the effectiveness of this method to study the magnetic
anisotropy, interactions and relaxation phenomena in nanostructured
materials.
·
We have expanded
our research activities to include film growth and nanoparticle
synthesis using soft chemical methods based on Langmuir-Blodgett
and spin coating. While we continue to obtain materials for our research from
collaborators, we now have the capability to synthesize and process our own
materials. We routinely synthesize various metal oxide nanoparticles
in the size range of 5 to 20 nm using chemical methods. More recently, in
collaboration with Dr. Matthews at USF, we have built a CVD reactor to grown
carbon nanotubes from nanoparticle
catalysts.
·
Our current
interests include exploring surface anisotropy and contact-induced
ferromagnetism in carbon nanotubes. In a related
project, we are studying the viability of energy conversion and power
generation in hydrodynamically pumped ferrofluids through microchannel
arrays of nanotubes. This work is being funded by a
grant from DARPA/ARO
·
In a grant
supported by NSF, we are studying magnetocaloric
effect (MCE) in various magnetic nanoparticle
assemblies. Our goal is to explore the entropy change across the well known
blocking transition from the superparamagnetic to
frozen short range spin-ordered state observed in monodisperse
and polydisperse nanoparticles.
Can one actually use the MCE itself for practical cooling applications? It
appears that many of the promising large MCE materials have nanoscale
clusters. Moreover, the blocking temperature can be increased in nanoparticle systems by controlling the particle size
distribution as well as the inter-particle dipolar interactions mediated via
surfactant coatings.
·
It is important
to process nanoparticles with interesting physical
properties into functional structures for device applications. Recognizing this
need, we are working on synthesizing polymer nanocomposites
with magnetic nanoparticles doped in them using
several routes. We have successfully demonstrated uniform dispersion of the nanoparticles in polystyrene, PMMA, Polypyrrole.
The magnetic properties can be tailored systematically by varying the wt%
loading of nanoparticles into the polymer matrix. Recently,
we have grown spin-coated polymer nanocomposite bilayers with embedded nanoparticles
that exhibit superparamagnetism. Polymer films with superparamagnetic characteristics are expected to be very
useful for flexible RF electronics applications. This work will appear in a
forthcoming issue of Advanced Functional MaterialsThis
work is being funded by NSF-ECS division through a GOALI grant.
· We are interested in magneto-electric effect and multiferroic coupling in nanostructured and multilayered oxide structures. Using RF susceptibility and other experiments, we are exploring the coupling between elastic, magnetic and ferroelectric properties in CrO2/Cr2O3 heterostructures and other materials.
·
We have
successfully, for the first time, demonstrated growth of high quality composite
thin films as well as multilayer structures of Barium Hexaferrites
and Barium Strontium Titanates using magnetron
sputtering and PLD. These two oxides have excellent microwave properties and
our goal is to obtain materials with tunable electromagnetic response. This
system also has the potential for exhibiting multiferroic
coupling. We have been supported by a grant from DARPA/ARO for this work on
tunable oxides.
·
We have developed
a customized microwave probe station integrated to fit between the pole pieces
of a 0.8 T electromagnet. An 8753 VNA is used to measure the complex impedance
up to 6 GHz. This set-up is being calibrated and tested and will be used to
characterize the frequency response in magnetodielectric
films, multiferroic materials as well as nanoparticle arrays on substrates.
If you have any questions and want to know more about our research, please contact Dr. Hariharan Srikanth