Modeling of spins at zero and finite temperatures.

Not long ago, techniques for modeling and evaluating magnetic materials were too simplistic to reproduce accurately all the data obtained in experiments. But in 1995, researchers at Ames Laboratory, led by Bruce Harmon, developed a "spin dynamics" computational technique that can be used to accurately represent and evaluate the fluctuations of atomic moments (magnetic orientations) in solid magnetic materials at different temperatures. Among its benefits, the method can be used to make calculations of realistic-sized systems at temperatures of practical and scientific interest. Using this technique, scientists for the first time theoretically determined the magnetic moments in iron and nickel at high temperatures, even above a key temperature at which the magnetic moments vary in magnitude and point in random directions. Current studies focus on how and why specific defects in permanent magnets are crucial in determining desirable magnetic properties. Oak Ridge National Laboratory and collaborators used the technique in a record-setting supercomputer calculation.

Scientific Impact: The spin dynamics approach is a significant contribution to the foundations of a new theory of the dynamics of magnetic moments at finite temperature and in response to external applied fields. It enables scientists to model material properties at room temperature, at which magnets typically are used.

Social Impact: Metallic magnetism is key to many technologies, including magnetic data storage and electric power generation devices. Accurate modeling of computer bit switching is essential for the design of future high-density computer disks, and the capability to optimize high-temperature magnetic materials will lead to more energy efficient motors and transformers.

Reference: Phys. Rev. Lett., 75,729 (1995).

URL: http://cyclops.ameslab.gov/

Technical Contact: Daniel A Hitchcock, Mathematical, Information, & Computational Sciences Division, Office of Advanced Scientific Computing Research, 301-903-6767

Press Contact: Jeff Sherwood, DOE Office of Public Affairs, 202-586-5806

SC-Funding Office: Office of Advanced Scientific Computing Research