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Highlights

  • Magnetism behaves very strangely in compounds of lanthanum, strontium, cobalt and oxygen, and researchers have just attained new insight into the decades-old question of why. Pure LaCoO3 is a non-magnetic, narrow-gap semiconductor at low temperatures, but it acquires magnetic properties as the temperature is raised – in contrast with most materials, which tend to lose magnetism at higher temperatures. With strontium doping the magnetic properties become more prominent until, at 18% Sr, the compound becomes metallic and ferromagnetic, like iron. This behavior has often been...

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  • A new theoretical advance enables us to understand how the magnetic properties of a class of magnets called antiferromagnets respond to a magnetic field.  The theory describes the magnetic behaviors of both collinear antiferromagnets, in which adjacent magnetic moments point in opposite directions from atom-to-atom, and noncollinear antiferromagnets, where the magnetic moments rotate from one atom to the next.  Advantages of this theory include that it is expressed in quantities that are easily measurable and is useful for polycrystalline samples.  Applications of the...

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  • Significant LED performance improvements have been achieved by taking advantage of novel materials.An organic light emitting diode (OLED) requires at least one transparent electrode, which is most commonly indium tin oxide (ITO). While ITO is both transparent and a good electrical conductor, its light transmission differs from the other organic material layers used in the device, leading to internal reflections which reduce efficiency. Researchers replaced ITO with a special highly conductive polymer known as PEDOT:PSS. The new OLEDs have a peak power efficiency and other key properties...

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  • Scientists have discovered that the growth of iron on graphene — a one atom thick layer of carbon — occurs in an unusual way. For other metals the first atoms to arrive form small clusters on the graphene surface, and then the clusters migrate across the surface, seemingly at random. Whenever two clusters encounter each other, they merge to form a larger cluster, which moves a little slower. Growing these larger clusters is important for making electronic connections to graphene for microelectronic applications. Iron is different in that lots of small islands form, but they do not tend to...

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  • One of the best materials for converting heat to electricity just got 15% better. Adding a small amount of dysprosium to the thermoelectric known as TAGS-85 raises the thermoelectric figure of merit from 1.3 to 1.5.  Researchers examined the mechanism by which doping with dysprosium affects the thermopower.  The size of dysprosium along with its local magnetic characteristics modifies the interplay between electronic and thermal transport.  Dysprosium distorts the local crystalline lattice and enables higher energy carriers to move preferentially through the material....

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  • Researchers now understand why artificially engineered materials, known as metamaterials, can sometimes perform better than expected. Metamaterials are built from small, engineered structures that manipulate light in ways not found in nature. Unfortunately, energy is typically lost by theconversion of light to heat in the metallic components and typical support materials; this is a key challenge for application development. When a metamaterial is coupled with a support that has a so-called gain material at its surface, the results are unexpected —transmission losses are significantly...

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  • Researchers may have discovered the key to high temperature superconductivity — quantum criticality. A quantum critical point occurs where a material undergoes a continuous transformation at absolute zero. For superconducting cuprates and iron-arsenides, the curve of the superconducting transition temperature, Tc, versus doping (or pressure) is dome shaped. It wasn’t clear until now if superconductivity prevents a quantum critical point or if quantum critical behavior is hidden beneath the dome. An international team studied a barium-iron arsenic superconductor where arsenic is partially...

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  • Glass is often described as being like a liquid, with randomly arranged atoms.New insights are emerging that show some distinct levels of order within the structure of glasses. Our rapidly evolving understanding arises from new structural information made possible because of advanced light sources like the U.S. Department of Energy’s Advanced Photon Source. The new theory fits experimental data better than the widely accepted model based on icosahedral-like clusters. The new model shows many crystal-like polyhedra as well as clustering of polyhedra — features not seen in previous models....

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  • Advanced techniques have revealed what happens to the magnetism in an iron-arsenide superconductor when some of the iron atoms are replaced by iridium.Substituting some iron atoms by transition metals (TM) such as cobalt, nickel, platinum and iridium suppresses the magnetic order of the non-superconducting parent phases of the iron pnictides, which promotes superconductivity.  The way this happens remains one of the most intriguing puzzles in the field. A team of scientists has used x-ray resonant magnetic scattering at the DOE’s Advanced Photon Source to probe the local magnetic...

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  • Researchers have shown that it may be possible to make lasers using single-layer sheets of carbon atoms — the novel material known as graphene. Lasers are made from materials that can absorb ordinary light and then emit photons that have matching waves to provide high intensity.To generate laser power, a material must first undergo a population inversion where an excess of electrons is excited. They must then produce optical gain when one photon is emitted spontaneously causing the excited state electrons to undergo a cascade reaction, each one emitting an additional photon coherent with...

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