Physics Colloquia - 2005

Friday, Feb 11, 2005, 3:00pm

Professor Adam Kaminski, Iowa State University
High Temperature Superconductivity - Insights From Angle Resolved Photoemission Spectroscopy
Location: Physics 135

High temperature superconductivity is one of the most difficult problems in modern condensed matter physics. It exists (as far as we know) only in one family of materials (called cuprates) that contain quasi 2D CuO layers. In addition to high temperature superconductivity, these materials display a wide range of fascinating properties that cannot be understood within the framework of traditional models. Angle Resolved Photoemission Spectroscopy (ARPES) is an excellent technique to study electronic structure and interactions in these materials. In this talk I will discuss key results and new developments in this field.

Thursday, March 3, 2005, 3:00pm

Professor Brian Greene, Columbia University
The State of String Theory
Location: Chemistry 190

I will review the state of string theory, emphasizing its achievements to date and the open challenges it still faces. While the talk will be at the level of a physics colloquium, a significant part of the discussion will be more widely accessible.

Friday, March 31, 2006, 3:00pm

Frans Pretorius
Location: Physics 135

Tuesday, April 12, 2005, 3:30pm

Dr. Sarah K. Patch, Applied Science Lab, GE Healthcare
Thermoacoustic Tomography -- Data Reconstruction
Location: Physics 135

Thermoacoustic tomography (TCT) is a hybrid imaging technique that has been proposed by Kruger, et. al. as an alternative to xray mammography. Radiofrequency (RF) energy is deposited into the breast tissue uniformly in space, but impulsively in time. This heats the tissue causing thermal expansion. Cancerous masses absorb more RF energy than healthy tissue, creating a pressure wave, which is detected by standard ultrasound transducers placed on the surface of a hemisphere surrounding the breast. Assuming constant sound speed, the data represent integrals of the tissue's RF absorptivity over sphere centered about the transducers. R_{TCT} f(t,ω) = int_{θ in S{2}} f(ω + t θ) d theta The inversion problem for TCT is therefore to recover the RF absorptivity from integrals over spheres centered on a hemisphere. We present an inversion formula for the complete data case, where integrals are measured for centers on the entire sphere: f(x) = - Δ_{x} left( frac{1}{2π} ∫_{o in S{2}}left| x - o right| R_{TCT}f(left| x - o right|, o) d o right) We derive consistency conditions upon TCT data and discuss their implications for reconstructing clinically realizable 1/2-scan data sets.

Friday, April 22, 2005, 3:00pm

Dustin Kreft, Undergraduate Physics Major at UWM
Scanning Tunneling Microscopy (STM)
Location: Physics 135

STM is an elegant way of measuring the electron density of states on a surface and creates an image from the densities to show such features as surface properties and imperfections. I will describe how an STM is used to probe the surfaces of nanostructures, and its importance in industry. STM has also been used to move atoms and arrange them in a specific pattern to create micro-electromechanical systems (MEMS); such applications of this are heat and pressure sensors. We will view the simple concepts of how the STM technique works, the Physics behind it, and some of its uses. Hope to see you there!

Monday, May 2, 2005, 3:30pm

Professor Peter Rez, Arizona State University
The Physics of Electron Beam Cancer Treatments
Location: Physics 135

X rays with energies between about 4 MeV and 15 MeV and electrons with energies between 6 MeV and 20 MeV are widely used for treatment of many cancers. Electron beams are becoming popular in a number of areas, especially for tumors close to the surface. The aim of any treatment is to deliver sufficient dose to "kill" the tumor, while sparing as much of the surrounding structures as possible, and making sure that critical doses are not exceeded in sensitive areas. Calculation of dose (energy deposited/unit mass) for any proposed treatment is an essential part of the planning process. The simple algorithms that relate dose in the patient to measurements in water phantoms work well for soft tissues. For inhomogeneous regions such as air cavities, tissue-bone interfaces and lung tissue unacceptable errors can result from simple models. For this reason Monte Carlo methods are now gaining popularity though it is still the case that Monte Carlo calculations are too slow for routine clinical application. I shall review the physics of electron beam scattering for light elements and show that many simplifying approximations can be made while still maintaining sufficient accuracy for treatment planning purposes.

Friday, May 6, 2005, 3:00pm

Professor Aurel I. Popescu, University of Bucharest
Technical Performances of Living Organisms
Location: Physics 135

The living world is an exciting inexhaustible source of high performance solutions to the multitude of biological problems, which were attained as a result of the natural selection, during the millions and millions of years of evolution of life on Earth. In this talk I will present some examples of high performances of living beings, in the light of the universal principle of biological optimality, governing the realm of living matter. At the same time, the transfer of these optimal solutions, from living matter to techniques, is shortly discussed. This transfer is offering new and fertile perspectives to future technologies, which are claimed to be cheaper, more efficient and non pollutant.

Thursday, May 12, 2005, 3:00pm

Professor Ken D. Olum, Tufts University
Prospects for faster-than-light travel
Location: Physics 135

Is it possible to travel or to send a signal faster than the speed of light? Several ideas have been proposed. A signal "tunneling" through a barrier appears to arrive faster than the speed of light. Can information be sent rapidly through the barrier? Quantum mechanical particles can have correlations maintained over large distances. Can that effect be used to communicate instantaneously? Can one manipulate matter so that its gravitational effect will allow fast travel or communication? I will describe the status of these ideas and demonstrate some related phenomena (but not superluminal communication).

Friday, May 13, 2005, 3:00pm

Professor Shireen Adenwalla, University of Nebraska-Lincoln
Oscillatory Coupling of Magnetic Films Across an Antiferromagnetic Insulating Spacer Material
Location: Physics 135

The coupling of thin ferromagnetic (FM) films across spacer layers display a variety of behavior, the fundamental understanding of which has technological implications for the recording industry. FM films with metallic spacer materials display an oscillatory coupling, oscillating from ferromagnetically to antiferromagnetically coupled as the spacer film thickness is changed. The period of the coupling is related to the Fermi surface vectors of the spacer layer. The discovery of this coupling along with the accompanying giant magnetoresistance (GMR) led to the rapid development of GMR read heads, the device of choice in present day computers. If the metallic spacer layer is replaced by an insulator, the coupling decays monotonically with spacer thickness.

This talk addresses the coupling of two ferromagnetic thin films across an antiferromagnetic, insulating spacer layer, NiO. We measured oscillatory coupling across this insulating spacer layer, much to our surprise.[1] Subsequent measurements clearly indicate the role of the antiferromagnet as key to this oscillatory coupling. Our samples consist of ferromagnetic Co/Pt multilayers sandwiching the antiferromagnetic NiO. Detailed magnetization, magnetic x-ray scattering and magnetic imaging allow us to comprehensively build a picture of what is occurring. Element specific magnetization measurements reveal the magnetic behavior of the constituents viz. NiO and Co. The coupling may be explained by the canting of the antiferromagnetically aligned Ni spins which was theoretically predicted [2] and seen using x-ray magnetic circular dichroism (MCD) scans [3]. We have studied the element specific magnetization of Co and Ni as functions of field and temperature Element specific hysteresis loops showed identical behavior for both Co and Ni implying that the AFM NiO spins at the interface cant in the direction of the Co magnetization. The domain structure of the virgin samples indicated that weaker coupling produces larger domain sizes. Photo-emission electron microscopy (PEEM) images revealing the correlation between ferromagnetic domains in the Co and NiO layers. We will present our latest data as well as unanswered questions.

 [1] Phys. Rev. Lett. 91, 037207 (2003)
 [2] Phys. Rev. Lett. 92, 219703 (2004)
 [3] Z.Y. Liu, L. Gao, D. Keavney, S. Adenwalla Phys. Rev. B 70, 224423 (2004)

Thursday May 19, 2005, 2:00pm

Joshua Bostwick, Undergraduate Physics Major at UWM
Kane Dynamics
Location: EMS W220

For the most part, traditional dynamics deals with 18th century methods and their application to physically simple dynamical systems. At this time, an extensive knowledge of mathematics was needed to analyze these simple systems and thus more attention was focused on the "analytical mathematics of dynamics" than formulating the equations of motion. With the advent of modern computers all this has changed. Currently, the inability to formulate dynamical equations of motion can prove as large a hindrance, as solving these dynamical equations was formerly.

There exist multiple classical methods for deriving the dynamical equations of motion, such as vector approaches like Newton-Euler, and the scalar-variational approach of Lagrange. At times, these methods require large amounts of time and labor, without a significant reduction in the compactness of the equations of motion or numerical efficiency. Kane's method has the benefit of producing non-constrained systems of 1st order ODE's(Ordinary Differential Equations) for constrained systems, while both the Newton-Euler and Lagrange approaches yield 2nd order DAE's(Differential Algebraic Equations). Furthermore, Kane's method has the added benefit of dealing directly with non-holonomic (motion) constraints, without having to introduce and subsequently eliminate Lagrange multipliers.

This talk will introduce Kane's method in comparison with the methods of Newton-Euler and Lagrange through an example. We will see first hand the benefits associated with Kane's method.

Friday, May 20, 2005, 3:00pm

Professor Vladislav Yakovlev, University of Wisconsin-Milwaukee
Nanoscopic Optical Imaging in Vivo: From Science Fiction to Reality
Location: Physics 135

Friday, May 27, 2005, 3:00pm

Professor Alpan Raval, Claremont Graduate University
Problems and Insights in Network Biology
Location: Physics 135

Following the completion of the sequencing of whole genomes of various organisms, a flurry of experimental activity in biology has focused on different aspects of genome annotation, including the mapping of the network of inter-gene interactions of various types at the whole genome scale. This data can be viewed as information that is, in a sense, orthogonal to information present in the genomic DNA sequence alone. Important biological questions pertaining to evolutionary mechanisms and prediction of biological function can now be readdressed in the light of the new interaction data. This talk is divided in two parts. In the first part, I will discuss mathematical models of biological network evolution and their implications for evolutionary memory. In the second part, I will discuss how topological properties of interaction networks may be used to elucidate and perhaps predict biological function, and present recent results from the analysis of topological properties of various types of inter-gene interaction networks.

Thursday, June 16, 2005, 3:00pm

Professor Stephanie H. Curnoe, Dept. of Physics & Oceanography, Memorial University of Newfoundland
Recent Advances in Heavy Fermion Superconductivity
Location: Physics 135

I will discuss general properties of unconventional superconductivity in the context of two recently discovered heavy fermion superconductors (HFSC), PrOs4Sb12 and CePt3Si. PrOs4Sb12, the first Pr-based HFSC and the first HFSC among the family of filled kutterudite compounds, displays multiple superconducting phases, possibly described by a single, multi-component order parameter. The pairing mechanism is suspected to be neither phonons nor spin fluctuations, but rather quadrupolar (orbital) fluctuations. CePt3Si is an HFSC that lacks inversion symmetry, hence defying the usual classification in terms of singlet and triplet states. I will begin with an overview of experimental results. I will explain the role of group theory, especially representations, in the Landau symmetry analysis. Some technical details concerning gap function symmetry and phase diagrams will be given.

Friday, July 1, 2005, 3:00pm

Professor Sudeshna Banerjee, Tata Institute of Fundamental Research, India
Quest for the Invisible
Location: Physics 135

How does one look for very, very small particles invisible to the naked eye ??? Smash nuclei with enormous force and then use huge instruments to magnify the particles created in these collisions, so that the event becomes visible to us.

The field of Experimental High Energy Physics uses these huge machines and complicated techniques to look for tiny particles which are the basic building blocks of matter. A flavour of the machinery and the basic techniques used to identify such particles will be given in this talk.

One such particle is the heaviest sub-nuclear particle, the top quark. This quark was first seen at the Tevatron collider at Fermilab in 1994. But, till now only a few hundred of these quarks have been seen. Why is it so difficult to see this quark and other similar particles experimentally? This talk will explain some of the handicaps scientists face in their quest.

Web links for interesting information:
Accelerators at FermiLab
Collider Experiments at FermiLab
Compact Muon Solenoid at CERN

Friday, July 22, 2005, 3:00pm

Daniel R. Giese, Graduate Student, University of Wisconsin-Milwaukee
Methods of MgO(110) Surface Ordering
Location: Physics 135

The relative stability of the crystallographic faces of oxide surfaces is an intriguing new area of study. While the polar MgO(111) face, with its bulk-like surface composed of sheets of like anions or cations, is studied in terms of the polarity, these same arguments have traditionally been used to explain and predict neutral MgO(110) faceting. In a series of experiments the relative stability of the MgO(110) surface is explored. Previous faceting experiments are repeated to determine the origin of faceting, and the effect of temperature on faceting. In the process we observed an MgO(110) c(2x2) reconstruction, the first such discovery. The further observation, in profile, of the neutral MgO(001) and (110), and the polar MgO(111), allows the comparison of such surfaces after high temperature annealing.

Friday, August 26, 2005, 3:00pm

Professor Boldizsar Janko, University of Notre Dame
Manipulation of Spin and Charge in Magnetic Semiconductor Hybrids
Location: Physics 135

Magnetic semiconductors are known to exhibit giant Zeeman response with effective gyromagnetic ratios of order 100-1000. This property can be used to create spin-polarized charge textures with a highly inhomogeneous external magnetic field. I will discuss several hybrid systems in which the external magnetic field is supplied by either nanomagnets or superconducting vortices. In particular, I will show how recent progress in superconducting vortex manipulation can be used to manipulate spin and charge textures in magnetic semiconductors.

Friday, September 2, 2005, 3:00pm

Professor Myron B. Salamon, Dept. of Physics, University of Illinois at Urbana-Champaign
A Penetrating Analysis of Unusual Superconductors
Location: Physics 135

The discovery of new superconducting materials, including but not limited to the cuprates, has brought the realization that superconductivity comes in more flavors than originally contemplated by Bardeen, Cooper, and Schrieffer. A fundamental property of all superconductors is their ability to screen out magnetic fields except over a narrow region at the surface characterized by the penetration depth. This talk will discuss the nature of the penetration depth and demonstrate how its behavior can assist in identifying the nature of superconductivity in new materials. Among the examples to be described are materials that exhibit so-called triplet superconductivity.

Friday, September 9, 2005, 3:00pm

Professor Leslie (Lei) Ying, University of Wisconsin-Milwaukee
Parallel Magnetic Resonance Imaging
Location: Physics 135

Magnetic Resonance Imaging (MRI) has developed into a premier biomedical imaging modality by virtue of its ability to reveal the structure, metabolism, and function of internal tissues/organs of humans or any biological objects. However, MRI is known to have low imaging speeds, which has limited its practical application where imaging speed is an important issue, such as the case in cardiac imaging, dynamic contrast-enhanced cancer imaging, and functional neuroimaging. Parallel MRI using phased array coils has emerged as a promising technique to reduce scan time, thereby improve imaging speeds. There are still challenges to achieve high acceleration factors with large arrays. In this talk, I will present some state-of-the-art techniques as well as some new data acquisition and processing techniques developed in our group to address these challenges.

Friday, September 16, 2005, 3:00pm

Professor Abhay V. Ashtekar, Penn State University
Quantum Nature of the Big Bang
Location: Physics 135

According to general relativity, space-time ends at singularities and classical physics just stops. In particular, the big bang is regarded as The Beginning. However, general relativity is incomplete because it ignores quantum effects. Through simple models, I will illustrate how the quantum nature of space-time geometry sheds entirely new light on the nature of the big bang. Quantum physics does not stop there. Quantum geometry in the deep Planck regime can serve as a bridge to another, vast classical space-time. Abhay Ashtekar is Director of the Institute for Gravitational Physics and Geometry, and Eberly Professor of Physics at Penn State.

Friday, September 23, 2005, 3:00pm

Professor Brian McNamara, Ohio University
Outbursts from Supermassive Black Holes in Clusters of Galaxies and the Problem of Galaxy Formation
Location: Physics 135

The nuclei of giant galaxies located at the centers of galaxy clusters harbor billion solar mass black holes. These black holes and their host galaxies grow by accreting gas. The gravitational binding energy released by the inflowing gas regulates the growth of the black holes and the giant galaxies that harbor them. This situation mirrors the more general problem of baryon cooling and galaxy formation in the Universe.

Friday, September 30, 2005, 3:00pm

Professor Ying Liu, Pennsylvania State University
Odd-parity superconductivity in Sr2RuO4
Location: Physics 135

There exist two types of superconductors, the even- and the odd-parity ones, based on the pairing symmetry. In the past several years we have pursued phase-sensitive and tunneling measurements on Sr2RuO4 to determine its pairing symmetry, using SQUIDs consisting of Josephson junctions between an s-wave superconductor, Au0.5In0.5, and Sr2RuO4. We found that the phase of the order parameter changes by pi under inversion, making Sr2RuO4 the first odd-parity superconductor established by a phase-sensitive experiment. We have also measured single junctions of Au0.5In0.5-Sr2RuO4 prepared on a 90-degree corner and found evidence supporting a p-wave pairing state in Sr2RuO4 within the odd-parity scenario.

Friday, October 14, 2005, 2:15pm

Dr. Alexei Souslov, National High Magnetic Field Laboratory
Ultrasonic Studies in High Magnetic Fields
Location: Physics 135

The National High Magnetic Field Laboratory (NHMFL, or the 'magnet lab'), supported by the National Science Foundation, houses unique facilities for experiments in extreme environments such as very high magnetic fields and very low temperatures. It currently houses the world's most powerful 45T hybrid magnet and facilities to perform 900 MHz NMR. These facilities help us tease out some of the most fundamental properties of systems ranging from electronic solids to complex bio-molecules. I will begin with a survey of the facilities at National High Magnetic Field Laboratory, describing both the magnets and experimental facilities available to visitors from US and abroad. I will also give an overview of our 'Research Experience for Undergraduates' program, where we accept about twenty undergraduate interns each year. At NHMFL, I have been working to integrate several ultrasonic techniques with high magnetic fields and low temperatures. Ultrasonic methods provide very useful information about elastic, magnetic and electronic properties of solids. I will describe specific features of the pulse-echo technique, surface acoustic wave method and resonant ultrasonic spectroscopy. I will also present some of our recent experiments: investigation of the Fermi surface and the electron-phonon interaction in solids; studies of acconductivity in quantum dot arrays and in two dimensional structures with quantum Hall effect.

Friday, October 21, 2005, 3:00pm

Alexei Faustov , Ph.D., Defense Colloquium
Towards Nanoscopic Imaging Using Third Harmonic Generation in Submicron Spheres based on Optical Trapping Phenomenon
Location: Physics 135

It is well known that the optical microscopy resolution is limited by light diffraction (which approximately is a half of light wavelength or 250 nanometers). One way to "break" this limit is to scan an area of interest by illuminated aperture much smaller than the light wavelength (dozens of nanometers). This idea was realized in modern Scanning Near-field Optical Microscope (SNOM) with a fiber optic needle used as a probe. We propose to use an optically trapped nanoparticle instead of a scanning needle. It is known that both dielectric and metal nanoparticles can be stably trapped in 3 dimensions at the focal point of a laser beam. The trapped particle can be optically steered and it has an intrinsic property to radiate the third harmonic which is induced by the trapping or separate laser. Thus a scanning Third Harmonic illumination probe is formed. We present a prototype of a Scanning Near-field Optical Microscope (SNOM) based on this idea.

Friday, October 28, 2005, 3:00pm

Professor R.J. Dwayne Miller, University of Toronto
Making the Molecular Movie
Location: Physics 135

The picosecond barrier to high brightness electron pulses has been broken.
Femtosecond Electron Diffraction harbours great potential for providing atomic resolution to structural changes as they occur, essentially watching atoms move in real time --- directly observe transition states. This experiment has been referred to as "making the molecular movie" and has been previously discussed in the context of a gedanken experiment. With the recent development of femtosecond electron pulses with sufficient number density to execute nearly single shot structure determinations, this experiment has been finally realized. A new concept in electron pulse generation was developed based on a solution to the N-body electron progation problem involving up to 10,000 interacting electrons. This study determined the conditions for a new generation of extremely bright electron pulsed sources that minimizes space charge broadening effects, specifically for high time resolution applications in molecular imaging. This development represents a significant advance that has taken a gedanken experiment to reality. It is now possible to atomically resolve transition state processes. In this context, an atomic level view of melting has been obtained under strongly driven conditions for Al in which the process can be described within a thermally accessed barrier crossing. Subsequent studies of Au have helped further ellucidate the mechanism for the melt zone propagation. In addition to this line of study, applications to specific molecular systems will be discussed in the context of directly imaging reaction dynamics at the atomic level of inspection.

Friday, November 4, 2005, 2:00pm

Professor Dimitri N. Basov, University of California at San Diego
High-Tc superconductivity: summing up
Location: Physics 135

Discovered nearly 2 decades ago, high-Tc superconductors have consolidated a large fraction of the condensed matter community in the search for the mechanism leading to the transition temperatures as high as 160 K. In this talk I will overview recent developments in the experimental studies of high-Tc cuprates focusing on the results obtained by means of infrared spectroscopy. The crucial advantage of this technique is that one can get insights into the key characteristics of the superconducting state through a variety of model independent sum rules. Specifically, our group at UCSD has employed new analysis based on sum rules to examine the energy scales associated with the superconducting condensate and with the so-called pseudogap state. We believe that the sum rule results may be instrumental in narrowing down the field of plausible microscopic scenarios of high-Tc superconductivity.

Thursday, November 10, 2005, 3:00pm

Russell Fung, Ph.D., Defense Colloquium
Solution of the Phase Problem in Surface X-Ray Diffraction: Theory and Applications to Experimental Data
Location: Physics 137

Lack of phase information in typical x-ray diffraction measurements makes it very difficult to recover the atomic-scale structure of a crystal by direct inversion of the measured amplitudes. We have developed a direct method for surface x-ray diffraction (SXRD) to recover the part of the surface structure that is different from the truncated bulk. The iterative algorithm we have developed employs prior knowledge of the bulk structure and alternately satisfies constraints in real and reciprocal space. Continued information, pdf 108 kb

Friday, November 11, 2005, 3:00pm

Dr. Anthony Hudetz, Medical College of Wisconsin
Anesthetic Unconsciousness: An Elusive Phenomenon Studied With Brain Imaging and Electrophysiology
Location: Physics 135

Consciousness has been the subject of philosophical debate for centuries. Recent advances in brain imaging now permits the study of consciousness as a neuroscientific problem. A current approach is to contrast conscious and unconscious processes using paradigms borrowed from psychology and neuropsychology including bistable images, binocular rivalry, blindsight, change blindness, split brain, explicit-implicit memory, masked priming, etc. Another approach is to contrast a conscious and unconscious state that is, waking versus slow wave sleep, vegetative state, coma and anesthesia. To-date the mechanism of general anesthesia is unknown. Brain imaging with PET and fMRI has been applied to delineate critical brain regions affected by anesthetic agents. However, there are many difficulties. All agents produce specific changes with different spatial patterns. The latter may not reflect primary targets. Functional imaging shows blood flow changes that accompany metabolic demand and may not reflect subtle changes in neuronal spike patters used by the brain for information coding. The program to isolate conscious neuronal networks from the unconscious ones has not fulfilled its promise. Electrophysiological studies using EEG and event related potentials reveal critical temporal events on the ms scale that may distinguish between conscious and unconscious processes at a low spatial resolution. Mean field theories predict a phase transition in the global EEG upon loss of consciousness. Measurements with multielectrode arrays within the depth of cortex point to the importance of long-range cortico-cortical synchronization and late (200-400 ms) poststimulus oscillations for information processing that may be primarily affected by general anesthesia to produce unconsciousness.

Friday, November 18, 2005, 3:00pm

Professor Renee D. Diehl, Pennsylvania State University
Quasicrystals as Templates for Aperiodic Films
Location: Physics 135

Quasicrystals are new materials that are well ordered but not periodic. Their mechanical and electrical properties are very different from those of periodic crystals. Recent progress in the characterization and preparation of quasicrystal surfaces raises new possibilities for their use as substrates and templates in the growth of films having novel structural, electronic, dynamic and mechanical properties. The apparently unusual frictional properties of quasicrystals also evoke interesting fundamental questions about how physical properties are altered by quasiperiodicity. Our focus for the past several years has been to study the growth of films on quasicrystal surfaces, with a view toward producing 1-component quasicrystal structures, or quasiperiodically arranged nanostructures. Metal films on quasicrystal surfaces have been found to grow in a variety of modes, including the formation of quasiperiodic Cu multilayer structures, as starfish-like clusters of Al in quasiperiodic arrays, and in hexagonal dendrite structures of Ag on icosahedral AlPdMn. To obtain a more fundamental understanding of the growth process, we have recently studied and modeled the growth of Xe on decagonal AlNiCo. This growth process includes the formation of a quasicrystalline first layer followed by a transition to an fcc(111) structure. This talk will provide an introduction to many of the interesting features of quasicrystals and well as reviewing the recent progress in the area of film growth on their surfaces.

Friday, December 2, 2005, 3:00pm

Professor Laura Mersini, University of North Carolina at Chapel Hill
Legacy of Albert Einstein
Location: Physics 135

The impact of Einstein in cosmology, as well as recent developments in the field will be discussed.

Friday, December 9, 2005, 3:00pm

Professor Hariharan Srikanth, University of South Florida
Probing Magnetic Anisotropy and Interactions in Functional Nanostructures
Location: Physics 135

Magnetic nanostructures hold immense potential as basic building blocks in spin-electronic devices and high-density data storage. While it is an established fact that nanoparticles exhibit novel magnetic properties, in general, the ideal response is associated with isolated particles. In practical applications, one invariably has to consider functional nanostructures that consist of particle aggregates that are assembled or embedded in non-magnetic media. Precise mapping of fundamental parameters like the anisotropy and switching fields over a wide range in temperature and magnetic fields, is essential to understand the influence of relaxation, interactions, surface structure and other phenomena that govern the dynamic magnetic properties in these systems. RF transverse susceptibility experiments, developed by us, provide a very sensitive and unique way to probe these features. In this talk, I will provide an overview of our efforts in synthesis, structure-property correlation and experimental studies of the spin dynamics in functional magnetic nanostructures ranging from ordered arrays, polymer nanocomposites to diluted magnetic semiconductor (DMS) quantum dots. I will specifically focus on functionalities such as the role of magnetic nanoparticles in RF applications and magneto-caloric effect (MCE) for potential cooling of MEMS/NEMS devices. Work supported by grants from NSF and DARPA/ARO