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Being a racecar driver in NASCAR is a dangerous job. One small mistake can send cars flying, cause multi-car crashes and, in some cases, be fatal. Diandra Leslie-Pelecky explores the science behind some of the features in NASCAR that are designed to keep the drivers safe

Diandra Leslie-Pelecky reviews Racing Green: How Motorsport Science Can Change the World by Kit Chapman.

X-ray diffraction and transmission electron microscopy measurements of melt-spun Gd100−xFex (0 ≤ x ≤ 40) and inert-gas condensed/compacted samples (3.8 ≤ x ≤ 12.7) reveal a structure of crystalline hcp-Gd grains surrounded by a non-crystalline G d 1 − x e f f F e x e f f phase, where xeff > x is the effective iron concentration within the amorphous region. The two-phase structure is responsible for an unusual dependence of the coercivity on temperature in which non-zero coercivity is observed above the hcp-Gd Tc with a peak near 320 K. The coercivity decreases as the hcp-Gd grains order, then increases with decreasing temperature. This behavior is explained by the presence of magnetically correlated Fe-rich regions.

Speed is the ultimate goal of racing, and materials are an increasingly important area of research for making race cars faster. The splitter, which produces front downforce, is made from Tegris, a polypropylene composite offering comparable stiffness and improved impact properties at significantly lower cost than alternative materials. Engine blocks must be cast iron, but careful control of microstructure using precision manufacturing methods produces a lighter engine block that generates more horsepower.Speed and excitement must be balanced with safety, and materials are key players here, as well. Energy-dissipating foams in the car and the barriers surrounding the tracks allow drivers to walk away uninjured from accidents. Fire-resistant polymers protect drivers from high-temperature fuel fires, and technology transfer from the National Aeronautics and Space Administration (NASA) to the National Association for Stock Car Auto Racing (NASCAR) in the form of a low-temperature carbon monoxide catalyst filters the drivers' air.Sports are an outstanding way of showing the public how materials science and engineering are relevant to their lives and interests. Materials science and engineering is just that much more exciting when it's traveling at two hundred miles an hour.

There is significant interest in recent years in developing magnetic nanoparticles (MNPs) having multifunctional characteristics with complimentary roles. In this study, we investigated the drug delivery and magnetic resonance imaging (MRI) properties of our novel oleic acid-coated iron-oxide and pluronic-stabilized MNPs. The drug incorporation efficiency of doxorubicin and paclitaxel (alone or in combination) in MNPs was 74-95%; the drug release was sustained and the incorporated drugs had marginal effects on physical (size and zeta potential) and magnetization properties of the MNPs. The drugs in combination incorporated in MNPs demonstrated highly synergistic antiproliferative activity in MCF-7 breast cancer cells. The T2 relaxivity (r(2)) was higher for our MNPs than Feridex IV, whereas the T1 relaxivity (r(1)) was better for Feridex IV than for our MNPs, suggesting greater sensitivity of our MNPs than Feridex IV in T2 weighted imaging. The circulation half-life (t(1/2)), determined from the changes in the MRI signal intensity in carotid arteries in mice, was longer for our MNPs than Feridex IV (t(1/2)=31.2 vs. 6.4 min). MNPs with combined characteristics of MRI and drug delivery could be of high clinical significance in the treatment of various disease conditions.

Iron-based magnetic uids are widely used in physical applications. Recently, they have been extended to many biological applications due to their magnetic and biocompatible properties. However, their stability under an ambient environment still has not been systematically investigated. In this report, we present the oxidation process of magnetic uids. The oxidation process depends on the materials that make the nanoparticles, the di usion of oxygen atoms from the environment to the magnetic nanoparticles, which mainly depends on the viscosity of the solution and the surfactant that coats the nanoparticles. We suggest three ways to protect nanoparticles from oxidation: (a) using highly viscous carrier liquid (b) using relevant surfactants and (c) substitution of Ni2+ and Co2+ for Fe2+ in magnetite. Methods (a) and (b) are general, so they can be applied for many environmentally sensitive magnetic uids. Method (c) is speci c for a magnetite uid.

Women remain underrepresented in science professions. Studies have shown that students are more likely to select careers when they can identify a role model in that career path. Further research has shown that the success of this strategy is enhanced by the use of gender-matched role models. While prior work provides insights into the value of using role models, it does not explain the cognitive process involved in girls identifying role models from nontraditional careers for women. This feminist study addresses this gap by examining the cognitive process eighth-grade girls use in identifying a person as a science role model and comparing it to the process used by women scientists seeking to serve as possible science role models. Data revealed that the girls' process in identifying a role model involved personal connections and their initial image of a scientist led them to believe they could not have such a connection with a scientist. The initial views expressed by the women suggested they felt pressure to portray “perfect“ scientists in order to be a role model. A common understanding of a science role model was realized only after changes occurred in the girls' image of scientists and the scientists' image of a role model. The catalysts for these changes were the relationships that developed between girls and women scientists. © 2007 Wiley Periodicals, Inc. Sci Ed92:688–707, 2008

As university professors we sought to disrupt the practice of giving our students the actions we felt they should imitate in their teaching practice. Instead, we sought to actively engage teachers in the creation of workable solutions to real-life problems. We accomplished this by conducting a participatory action research project. This paper illustrates our action research project focused on preparing middle level science teachers to foster inquiry-based learning in their classrooms. The findings of this study not only lead to a revised professional development opportunity for science teachers, but also provided an example of university faculty engaging in pragmatic research focused on addressing contemporary issues in K-12 science education.

Teaching and learning continues to be driven by a version of professionalism that construes practice to be a form of applied science. This paper challenges that paradigm. In particular, subjecting and assimilating practical activity to a technical mode of rationality is challenged as not being the most appropriate way to approach teaching, learning, and the process that drives both of these phenomena, inquiry. Middle school science classrooms provide the contexts to explore the situated consequences of embracing the terms of inquiry. Placing inquiry at the core of the thinking and experiences of middle school science educators as a philosophical/theoretical/practical educative process to be worked with, and concomitantly, working as dynamic practice, yields working notions to be necessarily embedded, cultivating, sustaining, and nurturing inquiry in teachers’ practices. As teachers experimented directly with the working notions of seeing, relational knowing, mindful embodiment, and assessment as interrela...

We present preliminary results for a magnetic flow spectrometer for magnetic microparticle separation, and a magnetic flow cytometer for particle identification. The application of the instrument is to high-throughput bioassay. Here we report on the first application of our magnetic spectrometer to the sorting of ferromagnetic and superparamagnetic microspheres in flow. The system is based on a permanent magnet quadrupole and separates the polymer coated magnetic microspheres based on their magnetic moments. The cryogenic section of our magnetic flow cytometer, which involves SQUID-based detection of the sorted magnetic microspheres based on their magnetic moments, has been re-engineered to permit a smaller standoff between the SQUID array and the flowing magnetic particles. We present preliminary results with the new experimental setup, with an emphasis on both spatial and signal resolution.

Iron and cobalt nanoparticle fluids have been prepared by inert-gas condensation into an oil/surfactant mixture. Superparamagnetic iron fluids (mean particle size=11.6±0.4 nm) and ferromagnetic cobalt fluids (mean particle size=51.6±3.4 nm) produced by this technique are promising candidates for magnetic targeting and hyperthermia applications.

We have developed a novel water-dispersible oleic acid (OA)-Pluronic-coated iron oxide magnetic nanoparticle formulation that can be loaded easily with high doses of water-insoluble anticancer agents. Drug partitions into the OA shell surrounding iron oxide nanoparticles, and the Pluronic that anchors at the OA−water interface confers aqueous dispersity to the formulation. Neither the formulation components nor the drug loading affected the magnetic properties of the core iron oxide nanoparticles. Sustained release of the incorporated drug is observed over 2 weeks under in vitro conditions. The nanoparticles further demonstrated sustained intracellular drug retention relative to drug in solution and a dose-dependent antiproliferative effect in breast and prostate cancer cell lines. This nanoparticle formulation can be used as a universal drug carrier system for systemic administration of water-insoluble drugs while simultaneously allowing magnetic targeting and/or imaging. Keywords: Sustained release; wat...

Magnetic investigations on a nanocomposite material obtained by spinning solutions of styrene–butadiene–styrene block copolymer containing barium ferrite nanoparticles onto Si wafers are reported. The effect of the spinning frequency on the magnetic features is discussed. It is observed that the magnetization at saturation is decreased as the spinning frequency is increased as the centrifuge force removes the magnetic nanoparticles from the solution. This is supported by the derivative of the hysteresis loops, which show two components, one with a high coercive field and another with a small coercive field. Increasing the spinning frequency increases the weight of the low coercive field component. The anisotropy in the distribution of magnetic nanoparticles, triggered eventually by the self-assembly capabilities of the matrix, is revealed by the difference between the coercive field in parallel and perpendicular configuration. It is noticed that increasing the spinning frequency enhances this difference. The effect of annealing the nanocomposite films is discussed.

Zero- and finite-temperature coercivity mechanisms in disordered nanostructures are investigated by model calculations. Three different aspects are considered. First, it is shown that strongly reduced exchange in grain-boundary regions changes the power-law scaling exponent for the coercivity of random-anisotropy magnets. Second, it is analyzed how random interatomic exchange affects the thermal blocking and therefore the coercivity of spin glasses. Third, a master-equation approach is used to quantitatively elucidate the relation between the magnetic-viscosity regime and the sweep-rate dependence of the coercivity. A common feature of the considered mechanisms is that interatomic exchange creates nanoscale cooperative units which realize the coercivity in real space.

This study explored the effectiveness of bringing female scientists into the elementary classrooms on promoting changes in the stereotypical images of scientists. Qualitative and quantitative data were collected and analyzed to illuminate changes in stereotypical images of scientists. Results indicate that despite the efforts of the scientists to encourage the students to question their image of a scientist, the students held on to stereotypical images. Instead, the students questioned the true identity of the scientists, categorizing them as teachers. The results led to questions of the strength of the image and the extent of efforts needed for students to question that image.

Magnetic properties of SmCo 6.7− x Cu 0.6 Ti x Magnets ( x =0.25 and 0.30) are studied as a function of milling time and temperature. The samples were prepared by two methods: first by arc-melting and milling, and second by mechanical alloying from powders and subsequent annealing. The X-ray diffraction analyses show that the samples consist of 1:5 and 2:17 phases. Magnetic measurements show that the coercivity for samples prepared by arc-melting and milling increases with increase in milling time and it reaches a maximum of 8.1 kOe for x =0.30 and 5.3 kOe for x =0.25, and then decreases for both samples. The coercivities for the sample with x =0.30 are higher than the coercivities for the sample with x =0.25 for all milling times. High-temperature vibrating sample magnetometer magnetic measurements show that the coercivity for all samples decreases with increasing temperature from room temperature to 600°C. The sample prepared by mechanical alloying has higher coercivity (20 kOe at room temperature) than that prepared by arc-melting and milling for all temperatures under investigation. These materials have moderate energy products (1–10 MG Oe) and can be used for high-temperature magnetic applications.

Chemical synthesis has been used to produce Ni : Ni 3 C nanocomposites with Ni grain sizes from 5 to 60 nm and Ni 3 C grain sizes from 20 to 50 nm. The room-temperature coercivity and remanence ratio can be understood strictly in terms of Ni grain size; however, temperature-dependent measurements show that the Ni 3 C can affect the collective magnetic behavior by affecting interactions of the Ni particles.

Cis ferromagnetic, with a room-temperature coercivity of 70 Oe and a magnetization of 0.8 emu/g at 5.5 T,although the hysteresis loop is not saturated. The theoretical prediction that interacting locally nickel-richregions may be responsible for ferromagnetic behavior is supported by the observation of magnetically glassybehavior at low magnetic fields.I. INTRODUCTION

Mechanical milling of initially ordered ferromagnetic SmCo{sub 5} produces dramatic increases in coercivity after short (15 min to 1 h) milling times, accompanied by remanence ratios on the order of 0.7 and shifted hysteresis loops. X-ray diffraction shows that milling induces both chemical and structural disorder. The hysteresis-loop shift is continuous and nonlinear with temperature over the range 5{endash}300 K. The high coercivities are attributed to the formation of a nanostructure consisting of crystalline SmCo{sub 5} regions separated by a disordered interphase. {copyright} {ital 1999} {ital The American Physical Society}

Mechanical milling of ferromagnetic SmCo5 produces dramatic increases in coercivity or short (15 minutes to 2 hours) milling times. The milled nanostructured material is highly metastable and undergoes room-temperature recovery during the first two weeks after fabrication. Although changes in the coercivity with ageing time are significant, the diffracting crystallite size determined from x-ray diffraction remains constant. We conclude that disorder is a primary determinant of the coercivity of mechanically milled alloys.

Chemical synthesis at elevated temperature (200 °C) produces a highly disordered form of cobalt similar to that produced by mechanical milling. Annealing of the disordered phase produces material w...

We have used a reductive technique known to produce highly reactive metals to fabricate nickel and nickel-based nanostructured materials. The strong dependence of the magnetic, chemical, electrical, and optical properties of nanostructured materials are intimately correlated with material structure; thus, thorough knowledge of the effect of synthesis parameters on the structure is critical for the refinement of fabrication techniques. X-ray diffraction and electron microscopy are used to determine the effect of the synthetic conditions and subsequent processing on the material structure. Characteristic lengths of these materials range from 3 to 50 nm, depending on synthesis and annealing conditions. Annealing produces a metastable Ni3C phase that forms only in the presence of active carbon, suggesting that not only active nickel but also active carbon results from this process. The addition of P(Ph)3 affects the time and temperature dependence of the nickel crystallite growth, the temperature at which Ni3...

Understanding the correlation between magnetic properties and nanostructure involves collaborative efforts between chemists, physicists, and materials scientists to study both fundamental properties and potential applications. This article introduces a classification of nanostructure morphology according to the mechanism responsible for the magnetic properties. The fundamental magnetic properties of interest and the theoretical frameworks developed to model these properties are summarized. Common chemical and physical techniques for the fabrication of magnetic nanostructures are surveyed, followed by some examples of recent investigations of magnetic systems with structure on the nanometer scale. The article concludes with a brief discussion of some promising experimental techniques in synthesis and measurements.

Structural inhomogeneity on length scales comparable to magnetic interaction lengths can produce complex magnetic behavior. Crystalline GdAl2 is a ferromagnet with a Curie temperature of 170 K, while amorphous GdAl2 thin films exhibit classic spin-glass behavior with a freezing temperature of 16 K. Nanostructured GdAl2, made by mechanically milling initially crystalline GdAl2, exhibits ferromagnetic and spin-glass-like transitions; however, the spin-glass-like transition occurs at a higher temperature than the freezing temperature of amorphous GdAl2 thin films. Curie–Weiss analysis suggests that the paramagnetic-to-ferromagnetic transition is due to the ferromagnetic ordering of small GdAl2 clusters and that the glassy transition is most likely due to spin-glass-like ordering of a surface/interface phase.

The high-temperature coercivity of mechanically alloyed and subsequently annealed RCo/sub 5/ (R=Sm and Y) is studied. The annealed materials have the hexagonal CaCu/sub 5/ structure with 2:17 (or 1:7) regions as a minor phase. High-temperature magnetic measurements show that the coercivities of materials decrease with increasing temperature from room-temperature to 873 K, but that the temperature coefficient of the coercivity of YCo/sub 5/ is much smaller than that of SmCo/sub 6/. This behavior is explained in terms of the intrinsic temperature variation of the magnetocrystalline anisotropy.

Relaxation processes in disordered nanostructures and spin glasses are investigated by examining the role of the magnetic anisotropy. To abstract from freezing processes associated with phase transitions, the consideration is restricted to a one-dimensional bond-disordered Ising spin glass. Using a Mattis-type gauge transformation, the spin glass is mapped onto a disordered ferromagnet. Based on the behavior of the spin chain we argue that spin-glass freezing is not necessarily related to a phase transition. The magnetic anisotropy, which is largely ignored in the Glauber approach to Ising dynamics, gives rise to cooperative deviations from the Arrhenius behavior and mimics Vogel–Fulcher relaxation.

Mechanically milling SmCo5 powder significantly increases coercivity and remanence ratio by introducing defects; however, these defects can be removed by room-temperature aging, with a resultant decrease in coercivity. A series of (SmCo5)x:C1−x (0.15⩽x⩽1) samples has been fabricated to investigate the effect of C on oxidation protection and magnetic properties. SmCo5 was premilled for 1 h, then added to C powder and milled for times ranging from 15 min to 7 h. X-ray diffraction indicates the presence of crystalline graphite and SmCo5 for milling times ⩽6 h and also shows the presence of fcc Co for milling times >7 h. The magnetic properties are very weakly dependent on milling time after the C addition, which is attributed to the lack of further grain refinement. The saturation magnetization scales linearly with the wt % of SmCo5. Remanence ratios are approximately 0.7 and independent of volume fraction. The maximum coercivity of 16.5 kOe is comparable to the maximum obtained by milling SmCo5 without C. S...

This paper analyzes in-class worksheets as an active-learning technique in a large introductory physics class. Instructor and student evaluations of the worksheets are discussed, and suggestions for teachers interested in writing their own worksheets are made.

Reductive chemical synthesis is a versatile tool for fabricating elemental nanostructures; however, less work has been completed on understanding and controlling alloy formation. Magnetic Mg–Co and Mg–Co–C nanocomposites have been fabricated using a reductive chemical synthesis designed to produce highly active metals. The as-synthesized powder was annealed at temperatures from 150 to 650 °C. Samples were investigated using x-ray diffraction, alternating gradient force magnetometry, and superconducting quantum interference device magnetometry. X-ray diffraction indicates that the resulting structures are multiphase with MgCo2, MgCo3C0.5, fcc Co, Mg, MgO, and Li2CO3 present depending on annealing temperature. The temperature-dependent magnetization of the as-synthesized sample indicates ferromagnetic and antiferromagnetic or ferrimagnetic contributions. Increases in coercivity and remanance ratio with increasing annealing temperature are consistent with the formation and growth of small Co grains.

The goal of this work is to fabricate model nanomaterials with different types of disorder and use atomic-scale characterization and macroscopic magnetization measurements to understand better how specific types of disorder affects macroscopic magnetic behavior. This information can be used to produce magnetic nanomaterials with specific properties for applications such as permanent magnets, soft magnetic material for motors and biomedical applications.

It is essential to determine the biodistribution, clearance, and biocompatibility of magnetic nanoparticles (MNPs) for in vivo biomedical applications to ensure their safe clinical use. We have studied these aspects with our novel iron oxide MNP formulation, which can be used as a magnetic resonance imaging (MRI) agent and a drug carrier system. Changes in serum and tissue iron levels were analyzed over 3 weeks after intravenous administration of MNPs to rats. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (AKP) levels, and total iron-binding capacity (TIBC) were also measured with time to assess the effect of MNPs on liver function. Selected tissues were also analyzed for oxidative stress and studied histologically to determine biocompatibility of MNPs. Serum iron levels gradually increased for up to 1 week but levels slowly declined thereafter. Biodistribution of iron in various body tissues changed with time but greater fraction of the injected iron localized in the liver and spleen than in the brain, heart, kidney, and lung. Magnetization measurements of the liver and spleen samples showed a steady decrease over 3 weeks, suggesting particle degradation. Serum showed a transient increase in ALT, AST, AKP levels, and TIBC over a period of 6-24 h following MNP injection. The increase in oxidative stress was tissue dependent, reaching a peak at approximately 3 days and then slowly declining thereafter. Histological analyses of liver, spleen, and kidney samples collected at 1 and 7 days showed no apparent abnormal changes. In conclusion, our MNPs did not cause long-term changes in the liver enzyme levels or induce oxidative stress and thus can be safely used for drug delivery and imaging applications.

Nanoparticles of bulk antiferromagnets often exhibit ferromagnetic behavior due to uncompensated surface spins. The peak temperature in the zero-field-cooled magnetization of $\mathrm{MnO}$\char22{}in contrast to other antiferromagnetic nanoparticles\char22{}has anomalous behavior, shifting to higher temperatures with decreasing nanoparticle size. We attribute this behavior to surface anisotropy enhanced by the specific occupancy of $3d$ levels in Mn, which produces a high-spin\char21{}low-spin transition not present in $\mathrm{NiO}$ nanoparticles.

Preface. Contributors. 1. Biological Applications of Multifunctional Magnetic Nanowires. 2. Nucleic Acid Delivery and Localizing Delivery with Magnetic Nanoparticles. 3. Magnetic Nanoparticles in Cancer Diagnosis and Hyperthermic Treatment. 4. Brownian Motion In Biological Sensing. 5. Dendrimers And Hyperbranched Polymers For Drug Delivery. 6. Nanogels: Chemistry to Drug Delivery. 7. Targeted Gold Nanoparticles for Imaging and Therapy. 8. Building Blocks of Nucleic Acid Nanostructures: Unfolding Thermodynamics of Intramolecular DNA Complexes. 9. Nanotoxicology. Index. About the Editors.

Chemical synthesis is a versatile technique for fabricating novel nanostructured materials. In the Rieke process, a metal salt is reduced by an alkali in a hydrocarbon solvent to form small, highly reactive particles. Synthesis at an elevated temperature (200/spl deg/C) increases the as-synthesized particle size and produces higher coercivities and remanence ratios than observed in similar syntheses at room temperature. The ratio of synthesis temperature to solvent boiling point appears to be an important parameter in both coercivity and oxidation resistance.

The effect of disorder on the ferromagnetic transition is investigated in mechanically milled $\mathrm{Gd}{\mathrm{Al}}_{2}$. $\mathrm{Gd}{\mathrm{Al}}_{2}$ is a ferromagnet when crystalline and a spin glass when amorphous. Mechanical milling progressively disorders the alloy, allowing observation of the change from ferromagnetic to a disordered magnetic state. X-ray diffraction and pair-distribution-function analysis are used to determine the grain size, lattice parameter, and mean-squared atomic displacements. The magnetization as a function of temperature is described by a Gaussian distribution of Curie temperatures. The mean Curie temperature decreases with decreasing lattice parameter, where lattice parameter serves as a measure of defect concentration. Two different rates of change with lattice parameter are observed: the first, slower rate occurs while grain size is changing, and the grain size is constant in the second regime. The breadth of the Curie temperature distribution is linear with lattice parameter. Milled and annealed $\mathrm{Gd}{\mathrm{Al}}_{2}$ shows that the mean Curie temperature has the same general dependence on lattice parameter as milled, but unannealed $\mathrm{Gd}{\mathrm{Al}}_{2}$, while the breadth of the Curie temperature distribution is different in annealed samples compared to the unannealed materials.

Biodegradable nanoparticles formulated from poly(D,L-lactide-co-glycolide) (PLGA) and polylactide (PLA) polymers are being extensively investigated for various drug delivery applications. In this study, we hypothesize that the solid-state solubility of hydrophobic drugs in polymers could influence their encapsulation and release from nanoparticles. Dexamethasone and flutamide were used as model hydrophobic drugs. A simple, semiquantitative method based on drug-polymer phase separation was developed to determine the solid-state drug-polymer solubility. Nanoparticles using PLGA/PLA polymers were formulated using an emulsion-solvent evaporation technique, and were characterized for size, drug loading, and in vitro release. X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) were used to determine the physical state of the encapsulated drug. Results demonstrated that the solid-state drug-polymer solubility depends on the polymer composition, molecular weight, and end-functional groups (ester or carboxyl) in polymer chains. Higher solid-state drug-polymer solubility resulted in higher drug encapsulation in nanoparticles, but followed an inverse correlation with the percent cumulative drug released. The XRD and DSC analyses demonstrated that the drug encapsulated in nanoparticles was present in the form of a molecular dispersion (dissolved state) in the polymer, whereas in microparticles, the drug was present in both molecular dispersion and crystalline forms. In conclusion, the solid-state drug-polymer solubility affects the nanoparticle characteristics, and thus could be used as an important preformulation parameter.

The ‘mad scientist’ stereotype is alive and well – and not an image most K-12 students can (or want to) embrace. Project Fulcrum, a National Science Foundation-funded GK-12 program, partners math, science and engineering graduate students with elementary and middle-level teachers. One project goal – broadening student images of science and scientists –is addressed by projects developed by the teacher/scientist teams that are focused on the specific needs of their students. The projects developed focus on scientists, the use of science in different types of jobs, and developing scientific skills. Pre-project research, in which teachers probe the motivation behind their students’ attitudes, is a critical component of developing a successful project. Although determining the specific impact of this project on student attitudes is complicated by its being part of a larger project, teachers and scientists report enhanced awareness of student attitudes and the reasons underlying those attitudes, and generated ideas to address those motivations.

The National Science Education Standards encourage teachers to become involved in research as ‘representatives of science in the classroom’. The Research Experiences for Teachers program affiliated with the Materials Research Science and Engineering Center at the University of Nebraska involves teachers in research on nanoscale magnetic and electronic structures over a summer. Two teachers and a sponsoring researcher share their experiences and what they believe are necessary elements for successful RET experiences.

Nanocomposite structures composed of ferromagnetic particles dispersed in a matrix are systems in which the magnetic properties can be tailored by varying the size and spacing of the ferromagnetic particles. Nanocomposites of SmCo/sub 5/ in a non-magnetic Nb/sub 0.33/Cr/sub 0.67/ matrix exhibit a wide variety of magnetic properties. SmCo/sub 5/ powder is premilled prior to mechanical alloying. The premilling results in a maximum coercivity of 16 kOe after 2 hours of milling, and an enhanced remanence ratio. Both features may be due to exchange anisotropy and/or exchange coupling between hard and soft ferromagnetic phases. The nanocomposite samples show that, when the SmCo/sub 5/ particulates are small enough, the primary effect of alloying is to disperse them throughout the matrix with no further refinement of size.

The role of disorder in magnetic ordering transitions is investigated using mechanically milled ${\mathrm{GdAl}}_{2}.$ Crystalline ${\mathrm{GdAl}}_{2}$ is a ferromagnet while amorphous ${\mathrm{GdAl}}_{2}$ is a spin glass. Nanostructured ${\mathrm{GdAl}}_{2}$ shows a paramagnetic-to-ferromagnetic transition and glassy behavior, with the temperature and magnitude of each transition dependent on the degree and type of disorder. Disorder is parametrized by a Gaussian distribution of Curie temperatures ${T}_{C}$ with mean ${T}_{C}$ and breadth $\ensuremath{\Delta}{T}_{C}.$ A nonzero coercivity is observed at temperatures more than 20 K above the highest ${T}_{C}$ of any known Gd-Al phase; however, the coercivity decreases with decreasing temperature over the same temperature range where the ${\mathrm{GdAl}}_{2}$ grains ferromagnetically order. Models for the anomalous coercivity behavior are proposed and evaluated for their ability to explain the origin of the low-temperature glassy magnetization peak.

Measurements of DC susceptibility, AC susceptibility, and AC susceptibility with an applied DC bias field were performed on mechanically milled GdAl2. A paramagnetic phase exists above a temperature T ≈ 140 K. However, there are significant deviations from the Curie-Weiss Law in this temperature regime, suggesting multiple magnetic components. Fits to the high temperature data show that two Curie-Weiss terms represent the data quite well. Below 140 K one of these magnetic components becomes ferromagnetic as indicated by a shoulder in the AC susceptibility and DC susceptibility data. This ferromagnetic component is suppressed by the application of sufficiently strong DC bias field. Accompanying this shoulder is a peak at lower temperatures (T < 50 K), which suggests the existence of another component that is magnetically glassy in nature. The two-component behavior of mechanically milled GdAl2 can be explained in terms of the nanostructure of the material, which consists of nanometer-sized grains and a disordered interphase.

This research is focused on (1) design of novel nanocomposite structures for high energy-product permanent magnets, (2) design of enhanced high-temperature Co-based alloys by compound-alloy modifications, and (3) development of enhanced hard and soft magnets via novel processing methods including mechanical alloying, cluster-assembled materials, and rolling techniques. Model nanocomposite hard-soft combinations have been developed with energy products of about 50 MGOe and coercivities of about 40 kOe. A theoretical understanding has been achieved of the structural characteristics needed to produce high energy products in the exchange-coupled nanocomposites. A variety of 2:17, 1:7, 5:17 and modified compounds have been investigated both experimentally and theoretical. It has been shown that transition-metal additions such as Ti, Cu, and Zr, are capable of stabilizing the disordered hexagonal Sm(CoM)7 phase with beneficial increases in anisotropy. Considerable development work on processing methods has been performed in this period.

Mechanical milling provides a unique means of studying the influence of grain size and disorder on the magnetic properties of nanostructured alloys. This paper compares the role of milling in the nanostructure evolution of two ferromagnets – SmCo5 and GdAl2 – and the subsequent impact of nanostructure on magnetic properties and phase transitions. The ferromagnetic properties of SmCo5 are enhanced by short (< 2 hours) milling times, producing up to an eight-fold increase in coercivity and high remanence ratios. The coercivity increase is attributed to defect formation and strain. Additional milling increases the disorder and produces a mix of ferromagnetic and antiferromagnetic interactions that form a magnetically glassy phase. GdAl2, which changes from ferromagnetic in its crystalline form to spin-glass-like in its amorphous form, is a model system for studying the dependence of magnetically glassy behavior on grain size and disorder. Nanostructured GdAl2 with a mean grain size of 8 nm shows a combination of ferromagnetic and magnetically glassy behavior, in contrast to previous studies of nanostructured GdAl2 with a grain size of 20 nm that show only spin-glass-like behavior.

We have prepared and studied iron-oxide nanoparticles coated with oleic acid (OA) and Pluronic® polymer. The mean diameter of the iron-oxide nanoparticles was 9.3(±)0.8nm. Saturation magnetization values measured at 10K varied from 66.1(±0.7)emu∕gto98.7(±0.5)emu∕g. At 300K the loops showed negligible coercive field. The peaks in zero-field-cooled susceptibility decreased from 280to168K with increasing OA concentration up to 10.6wt%, and remained nearly constant for higher concentrations. This suggests that incomplete coverage of the OA allows small, interacting agglomerates to form.

Initially crystalline GdAl2 was mechanically milled for long times to produce a highly chemically disordered phase with approximately 8‐nm grains. Analysis of dc magnetization measurements using an Arrott plot and the approach to saturation suggest the presence of significant random anisotropy. ac susceptibility measurements showed that the shift in the peak temperature with frequency usually seen in magnetically glassy and superparamagnetic systems was virtually undetectable in the 10–1000‐Hz frequency range. Based on these results, we believe that this material represents an interacting system with random anisotropy, where the anisotropy is the result of surface and interface asymmetries.

Self‐stabilized magnetic colloids consist of magnetic particles dispersed in an appropriate matrix. Fixing the particles in a stabilizing matrix has the advantage of preventing particle agglomeration, increasing resistance to oxidation, and allowing control over the interparticle spacing and particle size. We describe the chemical synthesis of cobaltnanoparticles in a polystyrene/triphenylphosphine polymer matrix. Depending on the synthesis parameters, magnetic properties of the as‐synthesized nanocomposites range from superparamagnetic to ferromagnetic with coercivities on the order of 130 Oe. Solvent choice and polymer crosslinking significantly affect the magnetic properties. Annealing in vacuum produces coercivities of up to 600 Oe and remanence ratios of up to 0.4. Measurement of the isothermal remanence magnetization and dc demagnetization indicate the presence of both magnetizing and demagnetizing interactions, in contrast to particles synthesized without the polymer, which show no evidence for magnetizing interactions. The zero‐field‐cooled temperature‐dependent magnetization displays a cusp, while the field‐cooled magnetization increases monotonically below the cusp temperature. Glassy behavior is observed for temperatures below the cusp, although the mechanism producing this behavior is not yet understood.