Electric field utilized to locally pin magnetic domain walls
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d would be long over.” Therefore, to study the bubble’s nucleation, Falk’s team used a computer model of a cube of a metallic glass made of copper and zirconium, measuring only about 30 atoms on each side. By definition, a bubble appears as a cavity in the digital block of metallic glass, with no atoms present within that open space. The simulations revealed that these bubbles emerge in a way that is wellpredicted by classical theories, but that the bubble formation also competes with attempts by the glass to reshuffle its atoms to release the stress applied to a particular location. That second process is known as shear transformation. As the glass responds to pressure, the researchers found which of the two processes has the upper hand—bubble formation or shear
transformation—varies. They determined that bubbles dominate in the presence of high tensile loads. But when the pulling forces were small, the atom reshuffling process prevailed. Falk and his colleagues hope their findings can help scientists developing new metallic glass alloys for products that can take advantage of the material’s high strength and elasticity, along with its tendency not to shrink when it is molded to a particular shape. These characteristics are important for applications, for example, in cell phones and computers. “Our aim is to incorporate our findings into predictive models of failure for these materials,” Falk said, “so that they can be optimized and used in applications that require materials that are both strong and fracture-resistant.”
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Electric field utilized to locally pin magnetic domain walls
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dvances in thin-film synthesis and characterization have enabled the development of electrically switched magnetic materials for novel memory applications. These devices are typically switched by substrate-strain transfer or electrostatic field effects, but such mechanisms are slow and of limited utility. Writing in the June issue of Nature Nanotechnology (DOI: 10.1038/ NNANO.2013.96; p. 411), researchers Uwe Bauer, Satoru Emori, and Geoffrey Beach at the Massachusetts Institute of Technology (MIT) now report an electric and magnetic field coupling mediated by magnetic domain wall pinning. The researchers describe new insight into fundamental defect-domain wall interactions and believe that such a mechanism may form the basis for faster, more efficient memories. The researchers first deposited thin-film heterostructures of Ta(4 nm)/ Pt(3 nm)/ Co(0.9 nm)/GdOx (3 nm) using dc magnetron sputtering and capped them with an array of Ta/Au gate electrodes. They chose this particular compound because the perpendicular magnetic anisotropy (PMA) of Co is sensitive to interfacial
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MRS BULLETIN
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VOLUME 38 • AUGUST 2013
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A series of polar magneto-optical Kerr effect microscopy maps showing expansion of a magnetic domain (blue) under an applied magnetic field of 170 Oe with increasing time (from left to right). Row (a) shows the material in its virgin state, without electric-field poling. In this case the domain propagates unpertur
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