Summer Investigations in Theoretical/Computational Condensed Matter Physics

This summer has been an exciting time for JMU's Complex Materials Group. Charles (Brock) Crook and Greg Houchins joined Dr. Haraldsen (@nuclearbologna) for some exciting investigations into computational and theoretical physics. Brock has been working on understanding magnetic interactions between impurities in graphene and Boron Nitride, while Greg has been working to determine analytical representations for the inelastic neutron scattering excitation coefficients of symmetric and asymmetric magnetic dimer systems.

Overall, we will be presenting our findings at the JMU Summer Research Symposium (July 29th and 30th) and we are planning to submit these articles for peer-reviewed publication.

Superexchange Interactions of Magnetic Impurities in Graphene

Graphene is a wonderful material that has very interesting electronic properties and has possible technological advantages. To help investigate how magnetic infusion can help this material break into the arena of spintronics, Brock is using Atomistic Toolkit to perform complex density functional calculations on different magnetic impurities in a supercell of graphene with 128 atoms (below). We are investigating changes in the magnetic and electronic structure and interactions with different variations of configuration and ion.

A supercell of graphene with 2 magnetic impurities (above) in the "star destroyer" configuration.

This name came from the obvious resemblance to the Star Wars(R) spaceship (below).

Image via Disney(R)

Understanding the Ground State Excitations in General S1-S2 Dimeric Systems

Understanding the fundamental interactions between magnetic moments is critical for pushing the science of spintronics and magnetic switching devices forward. Therefore, Greg has been working on calculating the inelastic neutron scattering structure factors for various excitations in mixed valence dimeric systems (two interacting spins of S1 and S2). This will allow for better understanding of larger systems since they are built on the foundation of subgeometric magnetic clusters. Through an analysis of these systems, Greg has been able to determine an analytical representation that will help experiments characterize the magnetic systems by looking at the relative intensities between excitations.

Magnetic splitting of a spin-1 and spin 1/2 dimer.

Infrared power generation: UPDATES

This summer the Undergraduate Students Kyle Britton, Justin Kaczmar and Graham Gearhart joined Harkirat Mann and Brian Lang to do research with Dr. Scarel!  Kyle and Justin are working on the the angular dependence of infrared power generation, while Graham is studying the relationship between the output of the infrared source with time and the voltage produced by the device used to harvest infrared radiation.  In July, Harkirat and Brian went to the Center of Nanophase Materials Sciences at the Oak Ridge National Laboratory (TN) to perform experiments with a laser emitting in the near infrared region.  Recently, a new paper from the group was accepted: H.S. Mann,Y. Schwab, B.N. Lang, J.L. Lancaster, R.J. Parise, and G. Scarel, “Effective thermoelectric power generation in an insulated compartment.  World J. Cond. Matter Phys. Vol. 4 (3), (2014).

Here is a figure from the paper: in thermoelectric power generation, the voltage trends in time follow faithfully the trends of temperature difference in the same time interval!  Simple but not trivial: in infrared power generation this symmetry is broken down!