Structural and magnetic properties of mechanically milled SmCo\u3csub\u3e5\u3c/sub\u3e:C

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 \u3e7 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. Samples exposed to air for times up to two months show no decrease in coercivity or remanence ratio for x ≤ 0.70. The addition of C has no detrimental effect on the magnetic properties obtained by milling, except the expected reduction of Ms. ©2001 American Institute of Physics

Bringing female scientists into the elementary classroom: Confronting the strength of elementary students\u27 stereotypical images of scientists

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 disordered Ni\u3csub\u3e3\u3c/sub\u3eC

The metastable Ni3C phase has been produced by mechanically alloying Ni and C. Ni3C particles of diameter 10 nm are produced after 90 h of mechanical alloying with no evidence of crystalline Ni in x ray or electron diffraction. Linear muffin-tin orbital band-structure calculations show that Ni3C is not expected to be ferromagnetic due to strong Ni-C hybridization in the ordered alloy; however, the introduction of even small amounts of disorder produces locally Ni-rich regions that can sustain magnetism. Mechanically alloyed Ni3C is 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-rich regions may be responsible for ferromagnetic behavior is supported by the observation of magnetically glassy behavior at low magnetic fields

Ecosystem Jenga!

Students are often taught that ecosystems are delicately balanced, But what. exactly, does this mean? How do we help students relate what they learn in the classroom about ecosystems to the world immediately around them? As scientists who work closely with middle school students as part of a National Science Foundation-funded Graduate Fellows in K-12 Education program called Project Fulcrum. we have learned that abstract concepts, such as delicately balanced ecosystem, are often not truly understood. We addressed this concern in a seventh-grade science classroom in Lincoln. Nebraska. by introducing students to locally threatened saline wetlands and the endangered Salt Creek tiger beetle (see Figure 1). To give students a tangible model of an ecosystem and have them experience what could happen if a component of that ecosystem were removed, we developed a hands-on. inquiry-based activity that visually demonstrates the concept of a delicately balanced ecosystem through a modification of the popular game Jenga. This activity can be modified to fit classrooms in other regions by focusing on a locally endangered plant or animal. which can be determined by contacting local governmental agencies (e.g .. Department of Natural Resources)

Self-Definition of Women Experiencing a Nontraditional Graduate Fellowship Program

Women continue to be underrepresented in the fields of science, technology, engineering, and mathematics (STEM). One factor contributing to this underrepresentation is the graduate school experience. Graduate programs in STEM fields are constructed around assumptions that ignore the reality of women’s lives; however, emerging opportunities may lead to experiences that are more compatible for women. One such opportunity is the Graduate Teaching Fellows in K–12 Education (GK–12) Program, which was introduced by the National Science Foundation in 1999. Although this nontraditional graduate program was not designed explicitly for women, it provided an unprecedented context in which to research how changing some of the basic assumptions upon which a graduate school operates may impact women in science. This exploratory case study examines the self-definition of 8 women graduate students who participated in a GK–12 program at a major research university. The findings from this case study contribute to higher education’s understanding of the terrain women graduate students in the STEM areas must navigate as they participate in programs that are thought to be more conducive to their modes of self-definition while they continue to seek to be successful in the historically Eurocentric, masculine STEM fields

Chemical Synthesis of Nanostructured Cobalt at Elevated Temperatures

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°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

Spin glass or random anisotropy?: The origin of magnetically glassy behavior in nanostructured GdAl\u3csub\u3e2\u3c/sub\u3e

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. ©2005 American Institute of Physic

Chemical Synthesis of Nanostructured Cobalt at Elevated Temperatures

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°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