1992 — 1998 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Nsf Young Investigator Award @ Carnegie-Mellon University
This research focuses on the physics of chemically prepared quantum dots. Four problems are targeted: controlling the quantum dot size and size distribution, fabricating arrays of quantum dots, generating samples with quantum dots in a semiconducting host, and understanding the role of the quantum dot-host interface.
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0.915 |
1995 — 1999 |
Majetich, Sara Mchenry, Michael (co-PI) [⬀] |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Synthesis Properties and Applications of Carbon-Coated Magnetic Nanoparticles @ Carnegie-Mellon University
9500313 Majetich Metal and alloy nanocrystals prepared in a carbon arc are interesting candidates for magnetic applications in xerography, magnetic resonance imaging, ferrofluids, data storage, and magnetic inks. Preliminary results demonstrate three potential advantages over existing materials: 1) the carbon coating prevents oxidation, 2) this process may be more efficient than other methods for preparing nanoparticles in the 10-100 nm size range, and 3) alloy nanoparticles with large magnetocrystalline anisotropy show room temperature magnetic stability. The research will explore scientific questions critical to the technical applications of these nanoparticles. One thrust area includes experiments to understand the formation of the carbon coating, and to correlate reaction parameters and particle morphology. This knowledge is used to optimize the growth process and to scale up production, both of which are essential for commercialization. The second thrust area focus as on magnetic characterization. Theoretical models of fine particle magnets are used to design nanoparticles with room temperature hysteresis required for data storage. After generation in the carbon are, the magnetic behavior of the nanoparticles are studied with DC and AC magnetometry, thermomagnetic analysis, Mossbauer spectroscopy, zero field NMR, and magnetic circular dichroism. The results are compared with technical benchmarks for the different applications to determine which possibilities are promising. New experimental data for alloy nanocrystals are compared with fine particle magnetism predictions to expand the fundamental understanding of hysteresis and switching rates in monodomain magnets.
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0.915 |
1998 — 2002 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Ordered Arrays of Magnetic Nanoparticles @ Carnegie-Mellon University
Abstract 9800127 S. Majetich, Carnegie Mellon University The objective is to prepare magnetic nanoparticle arrays in nonmagnetic matrices, and measure the interaction magnetic effects for various nanoparticle shapes from spheres to rods. A self-assembly method will be used to create monodispersed nano-sized nonmagnetic arrays that are transformed to a magnetic phase after solidifying the surrounding liquid. A second approach will consist in coating the particles in order to control interparticle spacing. Iron oxides are selected as the prototype material. Various characterization methods will be used to measure magnetic coercivity, magnetization directions of individual particles, interparticle coupling with the Faucault Lorentz microscopy, and nanoparticle moments by magnetic force microscopy. Simple particle interaction models will be developed to interpret the experimental results. The proposed particle synthesis methods and the investigation of the interparticle forces will provide fundamental information for development of magnetic data storage equipment. ***
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0.915 |
1999 — 2003 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Coercivity of Magnetic Nanoparticles and Nanocomposites @ Carnegie-Mellon University
9900550 Majetich
The magnetization reversal, or coercivity, of nanoparticles and nanocomposites is investigated on a nanometer scale using the Foucault method of Lorentz microscopy. Nanoparticles with extremely large or very small values of magnetocrystalline anisotropy are studied to extend existing models of coercivity. In high anisotropy ball milled SmCo5 nanoparticles the emphasis is on understanding the roles of strain, grain boundaries, and particle sizes in order to maximize the switching field. In low anisotropy Fe50Co50 nanoparticles minimal coercivity is desired, but it is unclear whether the best precursors to soft magnetic nanocomposites are superparamagnetic, or merely have low coercivity. The processing methods are varied to optimize the coercivities of the nanoparticles, whereupon they are compacted into nanocomposites. Cold isostatic pressing, magnetic compaction, and plasma pressure compaction are examined to determine the best method to yield the highest density without significant grain growth. Two types of nanocomposites with potential applications are examined, exchange spring magnets made by compaction of SmCo5 and Fe50Co50 nanoparticles and soft magnetic nanocomposites made by compaction of Fe50Co50 nanoparticles that have very thin carbon-rich coatings. Lorentz microscopy techniques are used to observe magnetization reversals on a submicron length scale. The microscopy results, in combination with standard methods to analyze the microstructure and chemical composition, identify the weak links that reduce the coercivity of a permanent magnet, or increase it in a soft magnetic material. The feedback guides the processing modifications required to optimize the magnetic properties of the nanocomposites. %%% This program examines exchange spring magnets, which could have higher energy products at lower cost than current high performance permanent magnets, and soft magnetic nanocomposites, which could have lower power losses, higher permeabilities, and greater stability than existing materials in niche applications at high temperatures or high frequencies. ***
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0.915 |
2000 — 2001 |
Hannon, James Majetich, Sara Feenstra, Randall (co-PI) [⬀] Garoff, Stephen (co-PI) [⬀] Suter, Robert [⬀] Sides, Paul (co-PI) [⬀] |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Acquisition of a Low-Energy Electron Microscope @ Carnegie-Mellon University
0079416 Hanon
Low-Energy Electron Microscopy (LEEM) is used to generate real-time images of surfaces with a lateral resolution of better than 10 nanometer. Surfaces can be imaged at arbitrarily high temperatures, and during growth. Contrast in LEEM arises because of differences in electron reflectivity at the surface, which reflect variations in the structural, chemical and magnetic properties of the surface. This award will help establish a LEEM facility at Carnegie Mellon University for use by an interdisciplinary group of researchers spanning four University departments. Proposed research projects include investigations of phase transitions at surfaces, two-dimensional coarsening and growth, step and phase boundary fluctuations, GaN growth, wetting of organic films, surface magnetism, growth at chiral surfaces, and texture development in thin film growth.
Low-Energy Electron Microscopy (LEEM) is used to generate real-time images of surfaces with a lateral resolution of better than ten nanomters, during growth, and at arbitrarily high temperatures. These unique features allow growth at surfaces to be studied in unprecedented detail. A LEEM facility will be established at Carnegie Mellon University for use by an interdisciplinary group of researchers. LEEM will be applied to a wide range of growth problems, from fundamental investigations of the chemistry and physics of surfaces, to process optimization in the development of new magnetic media.
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0.915 |
2002 — 2005 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Coated Monodisperse Magnetic Nanoparticles @ Carnegie-Mellon University
Proposal Number: CTS-0102747 Principal Investigator: S. Majetich Institution: Carnegie Mellon U. Title: Coated Monodisperse Magnetic Nanoparticles
ABSTRACT
The proposed project is on fabrication of well-ordered coated monodispersed Fe nanoparticle arrays with enhanced magnetic and electronic coupling between particles. This will result in collective phenomena such as exchange ferromagnetism, insulator-to-metal transition, and extremely large magnetoresistance. The PI is focusing her effort in this project on preparation of ultrathin but impermeable coatings on Fe nanoparticles, precise control over interparticle spacing, nanoscale structure-property relationships and their correlation to larger length scales.
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0.915 |
2005 — 2010 |
Majetich, Sara Zhu, Jian-Gang (co-PI) [⬀] Bain, James Kowalewski, Tomasz (co-PI) [⬀] |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Nirt: Single Particle Per Bit Magnetic Information Storage @ Carnegie-Mellon University
The objective of this research is to demonstrate a new magnetic recording paradigm using current-induced switching, which combines the advantages of patterned media, and the potential for lower manufacturing costs. This will be the first demonstration of single grain recording, and the smallest nanostructures yet investigated for current-induced switching. The approach will use self-assembled nanoparticle arrays as etch masks for patterning thin film multilayers into arrays of single particle bits. A conducting atomic force microscope probe will be used in contact mode to electrically contact individual bits. Low current densities will be used to sense the state of the bit, while high current densities will be used for switching. The noise power spectrum as a function of the applied current will reveal how effectively the spin torque is transferred. Simulations will be used to clarify the underlying physics.
This project will have broader impact in several areas. Two graduate students and several undergraduates will learn state-of-the-art techniques of nanoscale synthesis and fabrication, the use of scanning probe and electron microscopy for nanoscale structural characterization, and high sensitivity nanoscale transport measurement techniques. New science fair projects will be developed and the research of students in the Carnegie Mellon University/Milliones and Reizenstein Middle Schools Physics Concepts program will be supervised. Progress made in scanning probe-based recording, current-induced switching media, and the use of self-assembled structures for low cost, manufacturable nanopatterning will be significant for the magnetic recording industry.
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0.915 |
2008 — 2012 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Magnetic Nanoparticle Interactions: From Magnetostatics to Exchange @ Carnegie-Mellon University
TECHNICAL: Surfactant-coated nanoparticles have tremendous advantages due to their monodispersity and ability to form ordered arrays. Nanoscale magnetic measurements have demonstrated that uniformity in the particle size and spacing affects the collective dynamical response and the length scale of magnetic order. The surfactant controls the particle size distribution and provides mobility needed for self-assembly, but it also limits the range of interesting magnetic nanostructures that can be prepared. The typical 2-4 nm separation between cores means that interparticle coupling is almost purely magnetostatic. The surfactant provides at best a temporary, semi-permeable barrier to oxidation of materials such as iron and cobalt. Assemblies have the mechanical consistency of wax, making them unsuitable for most device applications. The surfactant makes it difficult to achieve good electrical contact, and varying amounts of surface coverage causes particle-to-particle differences in the apparent tunneling barriers. The project explores processing methods to prepare monodisperse metallic nanopillars in ordered arrays. The pillars will be made by reactive ion etching (RIE) a nanoparticle mask. In the simpler form the mask will be nonmagnetic and the magnetic particles will be created by sputter deposition on top of the dense pillar array. Direct patterning of magnetic multilayers with high density methanol-based plasma RIE will also be investigated to determine the minimum feature size and the effect of this dry etching process on magnetic response. The research focuses on systems where magnetic imaging and neutron reflectivity techniques will reveal temperature and field-dependent magnetic correlation lengths, which provides a deeper understanding of magnetic nanoparticle interactions. Manganese phosphide has a first order ferromagnetic to paramagnetic transition, so that the strength of magnetostatic interactions between MnP nanoparticles should change sharply with temperature. Ferromagnetic Co nanoparticles coupled to an antiferromagnetic (AF) IrMn layer may show differences in collective correlations due to exchange bias effects, depending on the AF domain size. Model soft nanocrystalline materials, with Fe pillars in a FeBSi matrix, will also be used to test the degree of exchange coupling between the nanoparticles in the array, which should change abruptly at the Curie temperature of the matrix, enabling quantitative comparison of exchange and magnetostatic contributions to the composite material. Finally the RIE of magnetic materials will be used to prepare some multilayer nanopillars where the small feature size leads to novel quantum confinement and spin accumulation effects. The intellectual merit of this project is in the development of a versatile, scalable process to prepare uniform magnetic nanoparticles and nanoparticle arrays in an inorganic matrix. The nanoscale characterization tools will reveal new features concerning the development of long-range magnetic order, and will clarify the interpretation of macroscopic measurements. NON-TECHNICAL: The work will have broad impact in numerous ways. It will form the thesis project for a graduate student and undergraduate research projects for several students. Hands-on demonstrations and laboratory experiments related to the magnetic phase transition in MnP will be developed for middle school students, and undergraduate physics laboratories.
This project is jointly supported by DMR?s Metals program and Condensed Matter Physics program.
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0.915 |
2008 — 2009 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Magnetic Nanostructures Gordon Research Conference; Centre Paul Langevin; Aussois, France; August 31 - September 5, 2008 @ Carnegie-Mellon University
2008 Gordon Research Conference: MAGNETIC NANOSTRUCTURES
This grant will provide supplemental support for graduate students, postdocs, and junior faculty who could not otherwise attend the 2008 Gordon Research Conference on Magnetic Nanostructures, held at the Centre Paul Langevin in Aussois, France, August 31- September 5, 2008. The conference will consist of a week of invited talks aimed at defining the state of the art of research in the field, and in identifying future directions. Another important purpose of this meeting is to provide a stimulating and welcoming atmosphere for more young scientists and members of under-represented groups to learn about hot fields and trends in their area, and to develop collaborative contacts with worldwide experts. Session topics will include semiconductor spintronics, complex oxide heterostructures, bio-nanomagnetism, magnetic nanowires and nanodots, domain wall excitation and motion, magnetic imaging, and ultrafast dynamics.
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0.915 |
2009 — 2012 |
Majetich, Sara Bain, James |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Investigation of Nanoscale Spin Dynamics With Scanning Probes @ Carnegie-Mellon University
"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."
This proposal will investigate the spin torque induced switching and ferromagnetic resonance dynamics of small patterned magnetic tunnel junction devices using scanning probe microscopy in several modalities. Scanning probes will be used to assist in the patterning of devices between 10 nm and 1 μm in size. Additionally, as previously demonstrated under NSF funding, scanning probes will be used to make electrical measurements on devices fabricated in this way. Custom probes developed for the delivery of the high currents needed for switching and for making measurements of FMR up to 10 GHz will be used and further developed. Samples for this work will be provided through collaboration with Everspin Technologies. The goal will be to quantify the role of size and shape of devices in the sub-100 nm range in determining critical current for switching and the onset of spin-torque induced resonance. These results will have application to memory as well as spin-torque oscillator devices in aggressively scaled technologies. The approach proposed in this work offers several advantages for the fabrication and characterization of spin-torque driven devices. Most importantly, testing with probes dramatically simplifies the fabrication challenges, reducing the patterning aspect ratio that is required, as well as eliminating leads and the need for planarization. Secondly, patterning with probes allows for very small features to be made with equipment of modest cost and complexity, amplifying the activities of the one graduate student who would be funded by this work. Finally, the scanned probe geometry can quickly test many devices to assess distributions and statistics, which will be central to success of spin torque driven devices both for memory and oscillator applications.
Technical Merit: The technical merit of this work is that it offers the ability to assess both DC and RF interactions among patterned spin torque devices, and the spread of these values. Clearer understanding and quantification of these distributions will enable the design of dense arrays for memory without unacceptable interactions, or, conversely, arrays of oscillators with interactions sufficiently strong to facilitate the coupling of many devices together and large power outputs. This will move us along on the development of a spin torque gain medium, or ?swaser?, as coined by Luc Berger, with enormous application to RF communications. We are taking a novel approach where we attempt to couple discrete oscillating elements with magnetostatic interactions, rather than continuous films to attempt to further quantize the allowed modes of the system.
Broader Impact: The broader impact of this work has two aspects. First is our strong industrial interaction. Everspin is following this work closely as it bears directly on future generations of technology they might develop. A second dimension of this broader impact of this work is the planned outreach activities that we will undertake. The PIs in this team have a proven track record working with undergraduates building artifacts. We will focus on implementing a first generation CMOS-MEMS scanned probe microscope on a chip. To do this we will enlist a small team of undergrads to design and prototype a CMOS-MEMS scanned probe microscope suitable for deployment in a classroom. While ambitious, we believe this is quite tractable for modest cost and complexity and will present an excellent learning opportunity for ECE and Physics undergraduates.
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0.915 |
2009 — 2013 |
Majetich, Sara Tilton, Robert (co-PI) [⬀] |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Magnetic Control and Optical Imaging of Nanoparticles For Biosensing @ Carnegie-Mellon University
0853963 S. Majetich
Intellectual Merit. The proposed research program will develop two types of plasmonic magnetic particles, and investigate the ability to control the motion of single particles magnetically while imaging them optically. Though these particles are smaller than the optical diffraction limit, their positions can be tracked by dark field optical microscopy through the surface plasmon resonance of the gold coating, or by fluorescence microscopy when fluorophores are bound to the particle surface. The rotation of rod-shaped particles will be monitored from the polarization of the longitudinal surface plasmon mode. Magnetically guided translation of nanoparticles is challenging because both viscous drag forces and random Brownian diffusion forces become significant for small sizes. Peclet number analysis suggests that it should be easier to control the motion of nanorods than nanospheres of the same volume, but current models of nanorod diffusion do not agree quantitatively. Another complicating factor is aggregate formation in aqueous dispersions. While electron microscopy shows highly monodisperse particle cores, the dispersions in water or biological media may contain aggregates with a broad size distribution. For single particle-based sensing as well as magnetic hyperthermia applications, the magnetic response will depend on the size of the aggregate, and optimal control requires uniform samples. We will coat 35-50 nm nominally spherical magnetite particles with gold, and then with polymers to form stable dispersions in phosphate buffered saline (PBS) solution. Our nanorod samples will be based on uniform but non-magnetic hematite nanorods ~300 nm long and 20 nm in diameter, that are reactively coated with thin layers of magnetite prior to the gold and polymer coating stages. The size of the agglomerates in aqueous and PBS dispersions will be determined from dynamic light scattering (DLS). The objective of the synthetic portion of the proposed research will be to prepare highly uniform, minimally agglomerated particles that show rapid magnetic response and have a strong surface Plasmon resonance. We will investigate the translational and rotational dynamics as a function of the applied field and field gradient first macroscopically by the AC magnetic susceptibility, and for the nanorods, optical modulation of the plasmon spectra. We will also construct an optical microscope cell with magnetic control for single nanoparticle and nanorod translation and rotation studies using dark field optical microscopy and fluorescence microscopy. The results will be compared with the predictions of ellipsoidal and cylindrical models of nanorod dynamics. In the final phase of the proposed work, these results will be used to explore new biosensing approaches where magnetic fields are used to move the particles and modulate their optical response. We will investigate magnetically guided translation within living cells to probe local viscosity and pH, and magnetically induced rotation to monitor selective binding events through the sensitivity of fluorescence intensity to the surface plasmons of the nanorods.
The Broader Impact aims will be linked with the research aims of the proposed program. A graduate student will be co-advised by the PIs. There will also be several undergraduate research projects involving magnetic, optical, and light scattering measurements on the particle dispersions. We have already recruited an African-American undergraduate to work on this project. A hands-on experimental module on ferrofluids and magnetic forces that will be developed for use in the Engineering Your Future program at Carnegie Mellon that targets middle school and high school girls, and also provides the opportunity to disseminate information to science teachers in the Pittsburgh Public Schools. This connection will be used to recruit a middle school teacher to work with us in creating age-appropriate classroom materials, demonstrations, and activities based on colloidal stabilization forces in both ferrofluids and plasmonic sols.
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0.915 |
2014 — 2017 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Magnetic Nanostructures Through Metallic Dewetting @ Carnegie-Mellon University
Non-technical Abstract:
This research program will investigate a new strategy for making nanoparticles of different metals and alloys, and characterize their size-dependent properties. Many electronic, magnetic, and optical properties become size-dependent when the material is structured on the nanometer length scale. Flash memory, magnetic recording media in computer hard disks, and diode lasers in digital video players, are examples of technology using nanostructured materials. The materials of interest in this research program are metals and alloys that have not yet been prepared as nanoparticles with good size control. The emphasis will be on alloys known to have interesting magneto-electronic or magneto-optical properties, or potential use as permanent magnets in energy-saving applications. The approach will use nanopatterned templates with regular arrays of pits to control the particle size. After depositing a thin film of the desired material, it will be heated until the film dewets and fills the pits. The uniform pit size will lead to a uniform particle size. This fabrication method will enable exploration of size-dependent behavior. Characterization of the magnetic, magnetoresistive, and magneto-optical properties will provide valuable new data that can be used in engineering nanostructured materials.
Technical Abstract:
This research program will investigate the formation of monodisperse magnetic nanoparticles created by the wetting and dewetting of thin metal films on nanopatterned templates, and to investigate their magnetic, magnetoresistive, and magneto-optical properties. While L10 FePt will be one of the target materials, there will be particular interest in magnetic metal alloys that have not yet been made by chemical methods, due to their oxidation sensitivity or complex crystal structures. The challenges are to overcome the sensitivity to oxidation that makes many of these particles impossible to prepare by solution chemistry methods, and to achieve crystallographic orientation to measure their anisotropic magnetic properties. There will be three strategies for preparing the magnetic alloy nanoparticle arrays, each with strengths and limitations: 1) shadow deposition on a nanoparticle monolayer, 2) deposition after seeding in nanohole arrays, and 3) using nanopillar arrays as a hard mask for a magnetic alloy thin film. In all cases rapid thermal annealing will be used to explore methods for crystallographically orienting the alloy nanoparticles. The templates will be dielectric materials (SiOx, SiNx, MgO) and conducting TiNx. The magnetic alloys will include L10 alloys, both familiar (FePt), and less studied (FeNi, MnAl, MnBi), materials for spintronics (the Heusler alloys Co2FeSi and Ni2MnGa, plus FeCoB), and for magneto-optics (the amorphous materials GdFeCo and TbFeCo). The results will lead to an improved understanding of metallic wetting and dewetting on the nanoscale. The nanopatterning process will be applicable to a wide range of complex materials, not only magnetic metal alloys. The preparation of monodisperse, passivated magnetic metal alloy nanoparticles will enable quantitative size-dependent measurements. The magnetization behavior will reveal the roles of surface chemistry and reduced exchange interactions at the particle surface. Novel resistance, magnetoresistance measurements will be made on individual nanoparticles. Smooth monolayer arrays of nanoparticles will be characterized by optical and magneto-optical spectroscopy. This project will involve the doctoral thesis research of a graduate student, along with several undergraduate research projects. There will also be impact to a broad audience through numerous educational activities associated with the magnetics community.
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0.915 |
2014 — 2017 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Broadband Conductive Atomic Force Microscopy For Studying Magneto-Electronic Nanostructures @ Carnegie-Mellon University
Conductive atomic force microscopy is a versatile tool for measuring nanoscale variations in the electrical resistance. The goal of this research program is to extend its capabilities over a broad range of frequencies to study magneto-electronic devices. Computers and smart phones contain nanoscale storage and logic devices that operate at high speeds, and in a race for smaller, faster, and more energy efficient electronics, many novel magneto-electronic devices are being explored. The new conductive force microscopy tool will enable rapid testing of prototype devices at different stages of nanofabrication, which will assist in optimizing the processing conditions and speed up the development cycle. In addition, the relevancy of the technique will be for magnetic hyperthermia cancer treatment, which uses excitation in the 100 kHz - 1 MHz range, for magnetically controlled heating. The outcome of this research will be related to educational and outreach activities of training graduate and undergraduate students and by demonstrating the principles of scanning probe microscopy through undergraduate research projects and the IEEE Magnetics Society.
The proposed research program will extend conductive atomic force microscopy to investigate thermal noise and magnetization dynamics in a spintronic devices at broad range of frequencies and by validating it operation through measurements on nanoparticles and nanodisks. Several kinds of magnetic nanostructures will be studied in order to test the operation of the high frequency scanning probe, and to gain new knoweldge at the nanosclae level. Crystallographically oriented nanoparticles will be patterned lithographically for investigation of the size-dependence of thermal fluctuations leading to superparamagnetic behavior, and isolated particles behavior applied to patterned nanoparticle assemblies with significant magnetostatic interactions. Patterned magnetic vortex structures will be investigated near their resonant frequencies (100-500 MHz). In the GHz range, the focus will be on ferromagnetic resonance of the oriented nanoparticles.
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0.915 |
2016 — 2018 |
Majetich, Sara Hunt, Benjamin (co-PI) [⬀] Feenstra, Randall [⬀] Gellman, Andrew (co-PI) [⬀] Skowronski, Marek (co-PI) [⬀] |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Mri: Acquisition of a Low-Temperature Scanning Tunneling Microscope For Advanced Surface Analysis @ Carnegie-Mellon University
Non-technical Abstract Five professors at Carnegie Mellon University will acquire a low-temperature scanning tunneling microscope (LT-STM), through the NSF MRI program. This instrument permits the mapping of atomic arrangements on surfaces, at low temperatures and under high magnetic fields. Studies will focus on "two-dimensional (2D) materials", that is, materials that are only one layer of atoms thick. In such materials, electrons are confined to move within the single atomic layer, and they thereby acquire certain novel properties that do not occur for regular, three-dimensional materials. Additionally, in the proposed work, different types of 2D layers will be stacked on top of another. Such combinations of 2D materials possess properties that, again, are unlike any found in regular, three-dimensional materials. For example, electrons are found to move much faster in 2D materials than in 3D materials, permitting the fabrication of novel types of electronic devices (useful for computers that are faster and require less power). Additionally, the magnetic properties of electrons in 2D are unlike anything that occurs in 3D, which also has potential for new types of computing devices. The LT-STM will have impact not only for the researchers at Carnegie Mellon University, but also more broadly for the "Pittsburgh Quantum Institute", which includes about 50 faculty from University of Pittsburgh, CMU, and Dusquesne University. The proposed LT-STM will serve as a powerful characterization tool for research projects undertaken by members of this Institute.
Technical Abstract Five investigators from Carnegie Mellon University (CMU) propose to acquire a low-temperature scanning tunneling microscope (LT-STM), including magnetic field capability. Two-dimensional (2D) materials and heterostructures will be studied. The 2D materials, which are only one or a few atomic layers thick, are formed by "exfoliation" from bulk crystals, that is, peeling off one or a few atomic layers from a bulk crystal and depositing those layer(s) on a suitable inert substrate. Such 2D layers exhibit a host of exotic properties including massless fermions, topologically protected states, superconductivity, and ferromagnetic phases, all of which will be probed in the LT-STM. Additionally vertical heterostructures will be formed by transferring one atomic layer atop the other; a state-of-the-art facility for performing such fabrication exists at CMU. Properties of the materials can be controlled in such heterostructures, since the presence of one layer in proximity to another yields collective behavior that differs from that of the individual layers. All of the investigators are active in directing graduate and undergraduate research, and the proposed LT-STM instrument will significantly enhance those activities. Additionally, the facility will impact theoretical studies presently performed at CMU related to the experimental work of the investigators. The instrument is also expected to have significant impact on the "Center for 2D Materials and Devices for Energy-Efficient Computing" at CMU, which four of the PIs are members of. An operating plan for the LT-STM has been formulated that will permit external users to have access to it. Four of the investigators are members of the "Pittsburgh Quantum Institute", which includes about 50 faculty from University of Pittsburgh, CMU, and Dusquesne University. The proposed LT-STM will serve as a powerful characterization tool for research projects undertaken by members of this Institute.
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0.915 |
2017 — 2020 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Superparamagnetic Tunnel Junctions For Logic Devices @ Carnegie-Mellon University
Superparamagnets switch back and forth between two stable states without requiring an external power source, using only thermal energy. This project will investigate the potential for a new type of low power computing using superparamagnets, where the switching frequency can be controlled by a small voltage or current. Nanofabrication techniques will be used to make electrical connections to individual superparamagnets, and then the superparamagnets will be coupled together. To evaluate the potential of this approach for probabilistic computing, logic gates and related devices will be built and tested. for performance and energy efficiency in multiplication and in logic operations. The results will be used to estimate the potential power reduction and processing speed of probabilistic logic gates based on superparamagnetic tunnel junctions. If superparamagnetic tunnel junctions can be optimized for reasonably fast, low power probabilistic computation, the results would have tremendous impact on sensors and hand-held electronic devices, where speed is less critical than battery lifetime. A graduate student will gain experience with nanofabrication and high frequency electronics. Hands-on and web-based demonstrations of logic gates will be developed for high school and middle school students, and both the graduate student and undergraduate researchers will be trained as STEM ambassadors, learning to communicate technical information to a broad audience.
The proposed research project will design, fabricate, and test superparamagnetic tunnel junctions that can be controlled by a voltage or current, for use in logic devices for probabilistic computing. Suparamagnetic tunnel junctions will be optimized for large changes in the telegraph signal over relatively small difference in the bias voltage or input current. Different alloys will be investigated to reduce the energy barrier for switching, and therefore the speed of the devices. Hard-wired devices will be fabricated, and the thermal switching rates as a function of bias voltage and input current will be measured using high frequency electronics. Following calibration of the individual superparamagnetic tunnel junctions, they will be coupled together into hybrid circuits and the resulting devices will be tested for use in probabilistic computing. Analog multiplication will involve two independent voltage-controlled superparamagnetic tunnel junctions and a CMOS AND gate. Here the time-average value of the output is predicted to be the product of the time-average values of the input signals. This operation is lower energy with probabilistic computing because it does not require analog-to-digital and digital-to-analog conversion steps. Groups of three interconnected superparamagnetic tunnel junctions will also be investigated as prototype logic gates (AND and OR). The output will be measured as a function of the bias voltages controlling the individual tunnel junctions to optimize the coupling strength between devices necessary for the truth table of the logic gate.
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0.915 |
2020 — 2023 |
Majetich, Sara |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Superparamagnets For Probabilistic and Reservoir Computing @ Carnegie-Mellon University
This research program aims to optimize superparamagnetic tunnel junctions for low power probabilistic and reservoir-based computation. The results will have impact on low energy sensors and hand-held electronic devices, as well as in high performance data encryption and probabilistic decryption. Superparamagnetic tunnel junctions are devices that spontaneously fluctuate between two resistance states, and have a time-averaged resistance that can be tuned using a smaller voltage than that needed for conventional switching, enabling lower power consumption, for example in a smart phone. Probabilistic computing performs logic operations based on combinations of the time-averaged signals. The randomness of the resistance fluctuations and ability to design superparamagnetic tunnel junctions for high speed are important features for cyber security applications. Reservoir computing is a type of hardware-based accelerator for neural networks, and here interacting superparamagnets will be used to form different kinds of reservoir. A unique feature is that only the input and output will require electrical connections, which could dramatically reduce power consumption. The aim of this component of the research program is to quantify the speed and short-term memory for different geometries of superparamagnet arrays, in order to evaluate them for use in artificial intelligence applications. The impact of magnetic reservoir computing would come from a better understanding of the algorithms that enable high energy efficiency and complex processing. A graduate student will develop extensive nanofabrication, high frequency electronics, and machine learning skills. There will be multiple options for undergraduate research projects, and a teaching module for a nanofabrication laboratory will be developed.
There are two interconnected thrusts to this research program, both centered on electrical control of superparamagnets. In the first, non-interacting superparamagnetic tunnel junctions are optimized for high average fluctuation rate and low bias voltage tunability of the time-averaged resistance. Multiple tunnel junctions are interconnected with variable feedback in order to demonstrate probabilistic logic gate behavior. The effect of the feedback amplitude and averaging time on the statistical preference for different logic states will be determined, and the power consumption measured, in order to benchmark superparamagnet-based logic devices. The second thrust involves investigation of assemblies of magnetostatically interacting nanomagnets for reservoir computing. They are controlled by the magnetic fringe field of a superparamagnetic tunnel junction input, and their response in picked up by the fringe field generated at a superparamagnetic tunnel junction output. Magnetostatically coupled patterns have previously been used for logic devices, but applications have been limited by the need for an external magnetic field. Here electronic control and detection will be used, enabling high speed operation and making integration with semiconductor electronics easier. Investigation of magnetostatically driven output coupling could eliminate an important bottleneck in the design of high performance magnetic logic devices imposed by the weak signal from the inverse spin Hall effect. By combining superparamagnetic tunnel junctions, electronic feedback, and magnetostatically coupled patterns, the proposed research program will develop an accelerator for machine learning and a toolkit for exploration of reservoir computing.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
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0.915 |