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Special Seminar

Multiferroicity in the New Spin-Spiral Antiferromagnets Cupric Chloride and Bromide CuX2 (X=Cl, Br)

by: Reinhard K. Kremer

Date: Monday August 16, 2010

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

The quest for new high performance multiferroic materials is stimulated by the expectation to effectively control magnetic properties by electric felds and, vice versa, the electric polarization by magnetic felds. Multiferroic materials may open new routes for novel magneto-optical and magnetoelectric high performance easily tuneable multifunctional energy effcient memory devices.

Spin-spiral multiferroics show a particularly strong sensitivity of the ferroelectric polarization to an external magnetic feld. Helicoidal magnetic structures can be established in one-dimensional magnets which are subject to magnetic frustration due to competing nearest and next-nearest neighbor superexchange and super-superexchange interaction along the chains. I review the properties and present recent results of one of the best investigated multiferroic systems, LiCuVO4, and discuss two new non-oxide spin-spiral magnet systems, CuX2 (X=Cl, Br) that also show multiferroic behavior.

Special Seminar

Superconducting Materials for Application

by: Mike D. Sumption

Date: Thursday May 06, 2010

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

In this presentation, an overview of OSU's CSMM/SuTC is presented, and the superconducting materials and applications under study there are discussed. Materials under investigation include Nb3Sn, MgB2, YBCO, and the oxypnictides. Studies of flux pinning in YBCO (as part of a collaboration with the AFRL) are briefly described, including pinning enhancement via nano-precipitates, both random and self assembled, along with their influence on Jc, Birr, and flux creep. This is followed by a discussion of phase formation and optimization studies of two very high performance Nb3Sn conductor types, one of which is a new design developed by OSU and commercial collaborators. After a brief description of initial efforts in the new oxypnictides, conductor development and materials property work for MgB2 is outlined. In this area, the talk focuses on the influence of the microstructure and connectivity on properties, in particular a newly discovered bifurcation in the magnetic and transport Jc as well as differences in irreversibility fields as determined by magnetic and transport techniques. A number of applications and application-relevant property investigations underway at the SuTC are then described. These include coil measurement and FEM modelling for MgB2, Nb3Sn, and YBCO prototype coils associated with applications in the areas of undulators, MRIs, rotors, and other specialty magnets. Efforts in YBCO conductor and cable AC loss, as well as YBCO coil-based quench propagation, are then discussed. Finally, modelling for MgB2 based fault current limiters is presented, as well as the set up of a facility for the testing of sub-scale MgB2 FCL coils.

Special Seminar

Spin Fluctuation and Unconventional Pairing in Iron-Based Superconductors

Prof. Jian-Xin  Li

by: Prof. Jian-Xin Li

Date: Thursday April 08, 2010

Time: 1:00 pm – 2:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Recently, the discovery of high-temperature superconductivity in iron pnictides has added a new class of materials to the family of high-Tc superconductors. In this talk, I will give a brief review of the progress of the theoretical understanding on their superconductivity and the related experiments, and report our theoretical works on the relation between the spin fluctuation and the pairing symmetry as well as the interplay between spin density wave and superconductivity in the vortex state in iron-pnictides.

Special Seminar

New Synthetic Approaches to Chalcogenide Nanoparticles - Molecular/Solid State LEGO - Chemical Concepts for Materials Design

by: Prof. Wolfgang Tremel

Date: Thursday December 10, 2009

Time: 4:00 pm – 5:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Not available.

Special Seminar

The Sonic Crystal and its Novel Efects

by: Prof. Yan Chen

Date: Friday October 23, 2009

Time: 11:00 am – 12:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

The sonic crystal, analogous to the photonic crystal, has been studied for over two decades. Some of its important efects, such as band-gap and dispersion relation, have been well established. Very recently, abnormal phenomena, such as negative refraction, enhanced transmission of acoustic waves in sub-wavelength, negative bulk modulus, negative mass density, etc., were found. The much lower velocity of acoustic waves as compared to light makes it easier to directly measure the sonic crystal's amplitude and phase of propagation, providing evidence for establishing the basic efects shared by both photonic and sonic crystals. On the large scale, sonic crystals with complicated artifcial structures could be easily introduced not only to give rise to some novel efects for which the physics is unclear in photonic crystals, but also to revolutionize acoustic device applications.

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