home  |  about us  |  contact  
 CSM Home
LDRD Proposal

Colossal Magneto Resistance


In October 2001, Apple Computer announced its new audio device, the iPod. This first generation device (on the left above) measured 4.02” x 2.43” x 0.78” and held 5Gb of data/music. Almost six years later, the iPod (right above) has grown to 160Gb of storage, while its overall size has decreased to 4.1” x 2.4” x .55”.

The iPod uses a compact disk driver as a storage media. The tremendous advances in storage capacity/density are due to increased understanding of the magnetic properties of metal oxides that exhibit “gigantic” or “colossal” magnetoresistance effects (CMR). Therefore, an understanding of CMR is important in data storage applications. One of the models for understanding CMR is quantum Monte-Carlo (QMC) simulations on a lattice.

In QMC simulations, each atom of the lattice is visited and the probability of a change (or event) is computed from all the eigenvalues of the Hamiltonian matrix. If a change is accepted, several entries in the Hamiltonian matrix are changed. After the entries are changed, all eigenvalues must be recomputed. A direct computation of all eigenvalues at every step is prohibitively expensive and limits the model to small 15 by 15 lattices. This model size imposes a limitation on the kinds of physical phenomena that can be studied. Oak Ridge National Laboratory is developing a method based on fast multipole method to incrementally update the eigenvalues from previously computed eigen-decomposition that is an order of magnitude faster than repetitive computation.

This algorithm will allow us to model larger 24 by 24 lattices. The move from 15 by15 to 24 by 24 will allow researchers to develop more complete and accurate understandings of the properties of materials which may have only been seen previously in partial form or influenced by finite system sizes.

For more information, please contact:

Ed D'Azevedo


   CSM Projects   
   Advanced Simulation Capability for Environmental Management (ASCEM)   
   The Center for Simulation of RF Wave Interactions with Magnetohydrodynamics (SWIM)   
   Coordinated Infrastructure for Fault Tolerant Systems (CIFTS)   
   Hybrid Multi-Core Consortium   
   Integral Equation Technology   
   MADNESS (Multiresolution Adaptive Numerical Environment for Scientific Simulation)   
   NEAMS Integrated Computational Environment (NiCE)   
   Nuclear Energy Advanced Modeling and Simulation (NEAMS)   
   Reliability, Availability, and Serviceability (RAS) for Petascale High-End Computing and Beyond   
  INCITE Allocated Projects  
   Advanced Simulations of Plasma Microturbulence at the Petascale and Beyond   
   Cellulosic Ethanol: Simulation of Multicomponent Biomass System   
   Climate-Science Computational Development Team: The Climate End Station II   
   High-Fidelity Simulations for Advanced Engine Combustion Research   
   High Fidelity Tokamak Edge Simulation for Efficient Confinement of Fusion Plasma   
   Investigation of Multi-Scale Transport Physics of Fusion Experiments Using Global Gyrokinetic Turbulence Simulations   
   Magnetic Structure and Thermodynamics of Low Dimensional Magnetic Structures   
   Nuclear Structure and Nuclear Reactions   
   Performance Evaluation and Analysis Consortium End Station   
   Petascale Modeling of Chemical Catalysts and Interfaces   
   Three Dimensional Simulations for Core Collapse Supernovae   
   Ultrascale Simulation of Basin-Scale CO2 Sequestration in Deep Geologic Formations and Radionuclide Migration using PFLOTRAN   
   Uncertainty Quantification for Three-Dimensional Reactor Assembly Simulations   
   Understanding the Ultimate Battery Chemistry: Rechargeable Lithium/Air   
  ORNL | Directorate | CSM | NCCS | ORNL Disclaimer | Search
Staff only: CSM computers | who, what, where? | news
URL: http://www.csm.ornl.gov/Highlights/CMR.html
Updated: Thursday, 29-Nov-2007 09:48:33 EST