Adjustable spin torque in magnetic tunnel junctions with two fixed layers

We have fabricated nanoscale magnetic tunnel junctions (MTJs) with an additional fixed magnetic layer added above the magnetic free layer of a standard MTJ structure. This acts as a second source of spin-polarized electrons that, depending on the relative alignment of the two fixed layers, either augments or diminishes the net spin-torque exerted on the free layer. The compound structure allows a quantitative comparison of spin-torque from tunneling electrons and from electrons passing through metallic spacer layers, as well as analysis of Joule selfheating effects. This has significance for current-switched magnetic random access memory (MRAM), where spin torque is exploited, and for magnetic sensing, where spin torque is detrimental.Comment: 3 pages, 2 figures, to appear in Appl. Phys. Let

Mechanisms limiting the coherence time of spontaneous magnetic oscillations driven by DC spin-polarized currents

The spin-transfer torque from a DC spin-polarized current can generate highly-coherent magnetic precession in nanoscale magnetic-multilayer devices. By measuring linewidths of spectra from the resulting resistance oscillations, we argue that the coherence time can be limited at low temperature by thermal deflections about the equilibrium magnetic trajectory, and at high temperature by thermally-activated transitions between dynamical modes. Surprisingly, the coherence time can be longer than predicted by simple macrospin simulations.Comment: 12 pages, 4 figure

Time-Resolved Spin Torque Switching and Enhanced Damping in Py/Cu/Py Spin-Valve Nanopillars

We report time-resolved measurements of current-induced reversal of a free magnetic layer in Py/Cu/Py elliptical nanopillars at temperatures T = 4.2 K to 160 K. Comparison of the data to Landau-Lifshitz-Gilbert macrospin simulations of the free layer switching yields numerical values for the spin torque and the Gilbert damping parameters as functions of T. The damping is strongly T-dependent, which we attribute to the antiferromagnetic pinning behavior of a thin permalloy oxide layer around the perimeter of the free layer. This adventitious antiferromagnetic pinning layer can have a major impact on spin torque phenomena.Comment: 5 pages, 4 figure

Fish scale remover machine

Laksa, sata and fish ball is a fish based food. Fish belong to groups of coldblooded animals. Fish lives in water, breathe through gills and use fins to move. According to the dictionary, scales are layered flaky skin on the surface of the fish skin. Scales function as a tool of defending them from their enemies. Hardness of fish scales are different depending on the types of fish being used for productio

Influence of melt feeding scheme and casting parameters during direct-chill casting on microstructure of an AA7050 billet

© The Minerals, Metals & Materials Society and ASM International 2012Direct-chill (DC) casting billets of an AA7050 alloy produced with different melt feeding schemes and casting speeds were examined in order to reveal the effect of these factors on the evolution of microstructure. Experimental results show that grain size is strongly influenced by the casting speed. In addition, the distribution of grain sizes across the billet diameter is mostly determined by melt feeding scheme. Grains tend to coarsen towards the center of a billet cast with the semi-horizontal melt feeding, while upon vertical melt feeding the minimum grain size was observed in the center of the billet. Computer simulations were preformed to reveal sump profiles and flow patterns during casting under different melt feeding schemes and casting speeds. The results show that solidification front and velocity distribution of the melt in the liquid and slurry zones are very different under different melt feeding scheme. The final grain structure and the grain size distribution in a DC casting billet is a result of a combination of fragmentation effects in the slurry zone and the cooling rate in the solidification range

Backpacker selves in a hostel: discourse, identity, and existential authenticity

Backpacker tourists are able to boldly lay claim to authenticity to local place—especially as they see themselves in relation to more (by their categorization) mainstream tourists—through the feeling of an authentic self that arises through backpacking tourism. Backpacker discourse about travel embodied travel experiences reflects and shapes sense of existential authenticity, a transformative travel euphoria in which the backpacker’s true identity is discovered through intense, sensuous experiences and perception of immersion in a foreign culture. This thesis uses ethnographic information and methods collected in a number of hostels—but primarily in Bogotá, Colombia—in order to demonstrate the relationship between the material, discursive, and phenomenological construction of identity and understanding of “authentic” local place. Through backpacking travel, these young travelers are constructing understanding of self, community, and the local, making backpacking a productive area of study for the study of tourist identity formation through language and bodily engagement

Mechanisms of grain refinement by intensive shearing of AZ91 alloy melt

The official published version of the article can be accessed at the link below.It has been demonstrated recently that intensive melt shearing can be an effective approach to the grain refinement of both shape casting and continuous casting of Mg alloys. In the present study, the mechanisms of grain refinement by intensive melt shearing were investigated through a combination of both modelling and experimental approaches. The measurement of the cooling curves during solidification, quantification of grain size of the solidified samples, and image analysis of the MgO particle size and size distribution in the pressurized filtration samples were performed for the AZ91 alloy with and without intensive melt shearing. The experimental results were then used as input parameters for the free growth model to investigate the mechanisms of grain refinement by intensive melt shearing. The experimental results showed that, although intensive melt shearing does not change the nucleation starting temperature, it increases the nucleation finishing temperature, giving rise to a reduced nucleation undercooling. The theoretical modelling using the free growth model revealed quantitatively that intensive melt shearing can effectively disperse MgO particles densely populated in the oxide films into more individual particles in the alloy melt, resulting in an increase in the MgO particle density by three orders of magnitude and the density of active nucleating MgO particles by a factor of 20 compared with those of the non-sheared melt. Therefore, the grain refining effect of intensive melt shearing can be confidently attributed to the significantly increased refining efficiency of the naturally occurring MgO particles in the alloy melt as potent nucleation sites.Financial support under Grant EP/H026177/1 from the EPSRC

An analysis of academic performance by discipline of community college transfer students

This study analyzed the academic performance of successful community college transfer students by academic discipline courses. Grade distributions were compared between Des Moines Area Community College (DMACC) and Iowa State University (ISU) by matched disciplines. A T-test for equality of means and chi-square analysis was used to determine significant differences in the grade distributions.;The participants included 837 transfer students that graduated with a bachelor\u27s degree from ISU between 1998 and 2002. Descriptive analysis of student demographics identified overall patterns and unique features of successful transfer students. Analysis of grade distributions of specific disciplines and community college general education courses identified significant differences.;The results of the study indicated a majority of transfer students were female, white, traditional age, with lower than State of Iowa average ACT scores. Almost half (48,2%) of the students transferred 60--65 credits and 66% complete the bachelor\u27s degree in 5 years. Overall GPA was significantly different between DMACC (2.96) and ISU (2.84). Significant differences were found in 20 of 31 matched discipline groups. DMACC general education grade distributions and ISU grade distributions were also significantly different. The results suggest that further research is necessary to analyze specific student characteristics and the related transfer success. Student support services and academic performance of community college courses will need further research. The significant differences in grade distributions suggest that faculty and administration of both institutions need to review course competencies, grading criterion and assessment techniques. Further research is warranted to better understanding specific community college academic performance and related university major fields of study. Community college courses specifically designed for transfer students may need to be developed in the general education curriculum to better prepare transfer students for university course expectations. Also, a comprehensive assessment program of general education skills and abilities may need to be implemented to more fully understand the academic expectations of transfer students