Engineering topics

Fisher, Ian

Publications and source records attributed to Fisher, Ian.

2 records

DOE OSTI2017

Lack of multiferroic behavior in BaCuSi 2 O 6 is consistent with the frustrated magnetic scenario for this material

BaCuSi 2 O 6 is a well-known quantum magnet that exhibits a Bose-Einstein Condensation quantum phase transition in applied magnetic fields. It contains Cu dimers that form singlets in zero magnetic field, and in applied fields as the singlet-triplet gap is suppressed a quantum phase transition occurs to canted XY antiferromagnetism between critical fields H c1 = 23 T and H c2 = 59 T. In addition, as the temperature is lowered, a rare frustrationinduced dimensional reduction has been proposed from three to two dimensions. Recently, however, a controversy has arisen about the details of the magnetic ordering due to the discovery of a tetragonal to orthorhombic structural transition at 100 K with an incommensurate modulation along the b-axis. Multiple magnon modes were observed in neutron diffraction studies, while NMR found modulation of the spin structure along both the ab plane and the c-axis. In this scenario the material is still a Bose-Einstein condensate system but the frustration is not perfect, calling into question the dimension reduction scenario. A recent study of BaCuSi 2 O 6 combining inelastic neutron diffraction and density functional theory suggest that the material isn’t even frustrated at all and that the spins are ordered ferromagnetically in the a-b plane and antiferromagnetically along the c-axis. After a detailed symmetry analysis we have concluded that the magnetic scenario postulated by this most recent unfrustrated theory6 will render BaCuSi 2 O 6 a multiferroic between H c1 and H c2 , with electric polarization in easy axis of the a-b plane for magnetic fields along the c-axis via an inverse Dzyaloshinskii-Moriya mechanism. Electric polarization is a sensitive symmetry probe of magnetic order, since magnetic systems that break spatial inversion symmetry can induce an overall ferroelectricity in the crystalline lattice. In pulsed magnetic fields we can detect electric polarizations with unique sensitivity to sub-pC/m 2 , which is orders of magnitude more sensitive than what can be detected in DC magnetic field.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Basic Research Needs Workshop on Quantum Materials for Energy Relevant Technology

Imagine future computers that can perform calculations a million times faster than today’s most powerful supercomputers at only a tiny fraction of the energy cost. Imagine power being generated, stored, and then transported across the national grid with nearly no loss. Imagine ultrasensitive sensors that keep us in the loop on what is happening at home or work, warn us when something is going wrong around us, keep us safe from pathogens, and provide unprecedented control of manufacturing and chemical processes. And imagine smart windows, smart clothes, smart buildings, supersmart personal electronics, and many other items — all made from materials that can change their properties “on demand” to carry out the functions we want. The key to attaining these technological possibilities in the 21st century is a new class of materials largely unknown to the general public at this time but destined to become as familiar as silicon. Welcome to the world of quantum materials — materials in which the extraordinary effects of quantum mechanics give rise to exotic and often incredible properties. To realize the tantalizing potential of quantum materials, there is much basic scientific research to be done. Recognizing the high potential impact of quantum materials, nations around the world are already investing in this effort. We must learn how the astonishing properties of quantum materials can be tailored to address our most pressing technological needs, and we must dramatically improve our ability to synthesize, characterize, and control quantum materials. To accelerate the progress of quantum materials research, the U.S. Department of Energy’s Office of Science, Office of Basic Energy Sciences (BES), sponsored a “Basic Research Needs Workshop on Quantum Materials for Energy-relevant Technology,” which was held near Washington, D.C. on February 8–10, 2016. Attended by more than 100 leading national and international scientific experts in the synthesis, characterization, and theory of quantum materials, the workshop identified four priority research directions (PRDs) that will lay the foundation to better understand quantum materials and harness their rich technological potential.

36 MATERIALS SCIENCE↗