MATHEON-ICM WORKSHOP on Free Boundaries and Materials Modeling - Abstract
Lebecki, Krzysztof
Nano-structures made of ferromagnetic material are attracting interest due to their potential application, mostly in computer devices. One possibility, already implemented, concerns storage of the information. Magnetic memories (MRAM) can preserve information without need for any power supply. Other discussed application concerns data transmission using movement of the domain walls, i.e. boundaries of regions magnetized in a different way. Recent progress in experimental techniques enables on the one hand better observation of the investigated phenomena. On the other, growth of more and more complicated or miniaturized structures is possible. Available theory, called micromagnetism, lacks however usefulness due to its complexity. Only few, simple structures, like homogenous sphere or infinite rod, can be evaluated analytically. In such a situation micromagnetic simulation is an attractive tool allowing both to explain the experimental results and to predict future phenomena or to plan necessary device geometry. There are a few micromagnetic popular simulation packages. Many of them are accessible in the public domain, some are commercially available. In any case magnetic simulation must be preceded by introduction of a mesh which will discretize the sample into distinct cells. Generally speaking, micromagnetic simulators belong to two different groups. So called finite-difference (FD) programs use regular mesh, where all cells are of same shape and size, usually right rectangular prisms. Less common, and more complicated are so called finite-element programs, where the mesh has a free structure, usually it is built-up from (different) tetrahedrons. I was involved with the development of most popular FD package called OOMMF. I have written an extension module to it allowing to use periodic boundary conditions in one dimension. This task is not trivial due to long range character of the magnetic interactions. Application of periodic boundary conditions enables to research elongated, quasi one-dimensional structures or samples possessing their own periodicity, like the magnetic storage devices, for example.