Magnetism

Materials Science Research Group

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One of the group's main research areas is the dynamics of magnetization switching in magnetic nanoparticles and ultrathin magnetic films. From a technological point of view, this area is important for its relevance to ultra-high-density data recording. Within a few years, we will reach recording densities so high that one bit will be written on a single, nanometer-sized particle. At these small sizes, the data will become vulnerable to thermal noise. (You would not want to have to carry your laptop around in a bucket of liquid helium.) In addition to the technological importance, the switching process is also a far-from-equilibrium, nonlinear physical phenomenon. This is an area of statistical physics that is not yet well understood. The main aim of our research is therefore to understand better the magnetization reversal mechanisms in such nanoscopic systems. The results of our research are important, both from a technological and a basic-science point of view. Some more detail at a popular level can be found at ./Recording[1].htm.

Selected graphics and movies for magnetism

From research supported in part by the NSF

Langevin micromagnetic simulations of nanoscale pillars.
Both still pictures and movies are available.
Movies show both pillars with small aspect ratio (24x24x120 nm) and pillars with a large aspect ratio (9x9x150 nm).
mpeg movie (about 4Mega)
of a Monte Carlo simulation for domain-wall motion in an Fe sesquilayer on W(110)
from the paper "Monte Carlo Simulation of Magnetization Reversal in Fe Sequilayers on W(110)" M. Kolesik, M. A. Novotny, and P. A. Rikvold. Phys. Rev. B 56, 11791-11796 (1997). Preprint: cond-mat/9706036. Smaller version of the movie (about 800K) .
Metastable decay in uniaxial magnetic models. Graphics showing the simulations for the homogeneous square-lattice Ising ferromagnet for both single-droplet (SD) decay and multi-droplet (MD) decay. Also photographs for the decay in the d=3 Ising model.
Is the probability of not switching in nanoscale ferromagnets a stretched exponential? A MATHEMATICA 3.0 fit to a Monte Carlo simulation of a 100x100 square-lattice Ising model using Glauber dynamics at 0.8T_c, fit with both a stretched exponential (gray dashed line) and an error function (red line) as predicted in our paper "Magnetization Switching in Nanoscale Ferromagnetic Grains: Description by a Kinetic Ising Model" J. Magnetism and Magnetic Materials, 150, 37 (1995). (The entire MATHEMATICA 3.0 notebook for the above.) From the paper ``Magnetization Switching in Single-Domain Ferromagnets.'' M. A. Novotny, M. Kolesik, and P. A. Rikvold. J. Magn. Magn. Mater., in press. Preprints: FSU-SCRI-97-90 and cond-mat/9710267.
An interactive JAVA simulation for the three dimensional Ising model in a magnetic field. his code was written by D.M. Townsley, an undergraduate student in our group. This model was used for the paper ``Projected Dynamics for Metastable Decay in Ising Models.'' M. Kolesik, M. A. Novotny, P. A. Rikvold, and D. M. Townsley. In Computer Simulation Studies in Condensed Matter Physics X, edited by D. P. Landau, K. K. Mon, and H. B. Schüttler, Springer Proceedings in Physics (Springer, Berlin, 1998), Vol. 83, pp. 246-251. Preprint: cond-mat/9703115, as well as for a longer paper in preparation.