Going Ashore in Thule

A Coast Guard member aboard The Westwind recounts his team’s adventures during the summer of 1961 in Thule. Articles, stories, and other compositions in this archive were written by participants in the Mighty Pen Project. The program, developed by author David L. Robbins, and in partnership with Virginia Commonwealth University and the Virginia War Memorial in Richmond, Virginia, offers veterans and their family members a customized twelve-week writing class, free of charge. The program encourages, supports, and assists participants in sharing their stories and experiences of military experience so both writer and audience may benefit

Magnetoresistance and anomalous Hall effect in micro-ribbons of the magnetic Weyl semimetal Co3_3Sn2_2S2_2

Magnetic Weyl semimetals exhibit intriguing transport phenomena due to their non-trivial band structure. Recent experiments in bulk crystals of the shandite-type Co$_3$Sn$_2$S$_2$ have shown that this material system is a magnetic Weyl semimetal. To access the length scales relevant for chiral transport, it is mandatory to fabricate microstructures of this fascinating compound. We therefore have cut micro-ribbons (typical size $0.3~\times~3~\times~50$\mu$m^3$) from Co$_3$Sn$_2$S$_2$ single crystals using a focused beam of Ga$^{2+}$-ions and investigated the impact of the sample dimensions and possible surface doping on the magnetotransport properties. The large intrinsic anomalous Hall effect observed in the micro ribbons is quantitatively consistent with the one in bulk samples. Our results show that focused ion beam cutting can be used for nano-patterning single crystalline Co$_3$Sn$_2$S$_2$, enabling future transport experiments in complex microstructures of this Weyl semimetal

Topological Hall effect in thin films of Mn1.5_{1.5}PtSn

Spin chirality in metallic materials with non-coplanar magnetic order can give rise to a Berry phase induced topological Hall effect. Here, we report the observation of a large topological Hall effect in high-quality films of Mn$_{1.5}$PtSn that were grown by means of magnetron sputtering on MgO(001). The topological Hall resistivity is present up to $\mu_{0}H \approx 4~$T below the spin reorientation transition temperature, $T_{s}=185$~K. We find, that the maximum topological Hall resistivity is of comparable magnitude as the anomalous Hall resistivity. Owing to the size, the topological Hall effect is directly evident prior to the customarily performed subtraction of magnetometry data. Further, we underline the robustness of the topological Hall effect in Mn\textsubscript{2-x}PtSn by extracting the effect for multiple stoichiometries (x~=~0.5, 0.25, 0.1) and film thicknesses (t = 104, 52, 35~nm) with maximum topological Hall resistivities between $0.76~\mu\Omega$cm and $1.55~\mu\Omega$cm at 150~K.Comment: 6 pages, 5 figure

Spin Hall magnetoresistance in antiferromagnet/heavy-metal heterostructures

We investigate the spin Hall magnetoresistance in thin film bilayer heterostructures of the heavy metal Pt and the antiferromagnetic insulator NiO. While rotating an external magnetic field in the easy plane of NiO, we record the longitudinal and the transverse resistivity of the Pt layer and observe an amplitude modulation consistent with the spin Hall magnetoresistance. In comparison to Pt on collinear ferrimagnets, the modulation is phase shifted by 90{\deg} and its amplitude strongly increases with the magnitude of the magnetic field. We explain the observed magnetic field-dependence of the spin Hall magnetoresistance in a comprehensive model taking into account magnetic field induced modifications of the domain structure in antiferromagnets. With this generic model we are further able to estimate the strength of the magnetoelastic coupling in antiferromagnets. Our detailed study shows that the spin Hall magnetoresistance is a versatile tool to investigate the magnetic spin structure as well as magnetoelastic effects, even in antiferromagnetic multidomain materials

Evolution of the Spin Hall Magnetoresistance in Cr2_2O3_3/Pt bilayers close to the N\'eel temperature

We study the evolution of magnetoresistance with temperature in thin film bilayers consisting of platinum and the antiferromagnet Cr$_2$O$_3$ with its easy axis out of the plane. We vary the temperature from 20 - 60{\deg}C, close to the N\'eel temperature of Cr$_2$O$_3$ of approximately 37{\deg}C. The magnetoresistive response is recorded during rotations of the external magnetic field in three mutually orthogonal planes. A large magnetoresistance having a symmetry consistent with a positive spin Hall magnetoresistance is observed in the paramagnetic phase of the Cr$_2$O$_3$, which however vanishes when cooling to below the N\'eel temperature. Comparing to analogous experiments in a Gd$_3$Ga$_5$O$_{12}$/Pt heterostructure, we conclude that a paramagnetic field induced magnetization in the insulator is not sufficient to explain the observed magnetoresistance. We speculate that the type of magnetic moments at the interface qualitatively impacts the spin angular momentum transfer, with the $3d$ moments of Cr sinking angular momentum much more efficiently as compared to the more localized $4f$ moments of Gd.Comment: 5 pages, 3 figure

Piaget and Engineering Education

Thomas Edison was a noted engineer while Jean Piaget made his fame in children’s educational psychology. Piaget’s “cognitive constructivism” has been adopted in many early childhood programs, but it also applies to engineering education and its “hands-on” approach, especially in laboratories and project-based courses. The direction of education dramatically shifted when Jean Piaget developed a child-centered developmental learning theory. According to his theory, children construct knowledge about their world through their active involvement in experiences that are meaningful for them in order to provide an ideal learning environment. A Piagetian classroom is filled with authentic activities designed to challenge students so they can construct knowledge at their own developmental pace. Creating constructivist learning environments where students construct their own meaning is not an easy task. Learners need opportunities to learn in a constructivist manner to effectively connect new ideas to existing schema. Educators must empower students to ask their own questions and seek their own answers, experience the world’s richness, and challenge them to understand the world’s complexities. Classroom instruction is frequently centered on delivering the content to students instead of facilitating student inquiry during the learning process. Although many of the principles of constructivism offer promise in the development of successful learning environments, practical applications are often hard to incorporate into the common constraints of the school environment.1 With the recent emphasis on “learner-centered” education in engineering education, a deeper understanding and application of Piaget’s work is in order. The purpose of this paper is to present a model of an engineering/education collaborative program that is built on Piagetian principles and attempts to outreach to K-12 students to build their enthusiasm for engineering and science. Thus, this paper will describe how Piaget’s work was continued by Seymour Papert who then introduced the idea of “constructionism” and how that concept applies to engineering education in the Toying With TechnologySM Program at Iowa State University (http://www.eng.iastate.edu/twt). A comparison of Piaget’s pedagogy and Edison’s work will demonstrate why this pedagogy has application in engineering