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Special Seminar

Nanostructures to Examine Strongly Correlated Materials: Magnetite

Prof. Douglas  Natelson

by: Prof. Douglas Natelson

Date: Thursday November 18, 2010

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Strongly correlated electronic materials, a huge class of materials for which single-particle band structure fails to describe their electronic properties, remain a topic of great interest. Such systems often exhibit competing electronic and magnetic phases, resulting in dramatic physical phenomena such as metal-insulator transitions and superconductivity. Magnetite, Fe3O4, is an archetypal strongly correlated transition metal oxide that, in bulk, exhibits a structural and electronic phase transition near 120 K from a moderately conducting high temperature state to a considerably more insulating low temperature state. The nature of the low temperature state remains a source of controversy after more than seven decades of investigation. Using nanostructure techniques and magnetite films, we demonstrate that it is possible to destabilize the insulating state with a sufficiently large in-plane electric field. We show that this destruction is not due to simple self-heating, and present evidence that suggests it is analogous to Landau-Zener breakdown of the correlated state, with disorder also playing an important role. Finally, we will use these studies to demonstrate that contact effects, scrupulously avoided in most experiments, provide additional insight into the conduction mechanism in this strongly correlated material.

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.

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