The main objective of this Focused Research Group (FRG) project is to bring together experimental, analytical and computational efforts in a comprehensive program in order to develop computational design tools for advanced microstructural engineering of multi-domain magnetic materials. The effort focuses on characterizing the interactivities between structural and magnetic domains with applied external fields and providing microstructural data to correlate the experimental structural and magnetic measurements with theoretical models. The analytical and computational efforts focus on generic model development and validation against existing experimental data.

Project Description

Some magnetic properties depend strongly on the microstructure of the material while others are relatively insensitive to microstructure. The former are usually termed extrinsic properties while the latter are designated intrinsic properties. In this research we will focus on the way in which external influences such as applied stress or magnetic fields affect the development of the microstructure in materials of importance to current technology. Included in the microstructure of magnetic materials is the distribution of the magnetic domains. One of the important technologies which utilize magnetic materials is the magnetic recording industry. Currently the density of magnetic storage on commercial disks for computers is about 10 Gbits/in2. As the density of recording increases the grain size of the magnetic materials used to store the information must also decrease to keep the signal to noise ratio acceptable. However as the grain size decreases the materials approach what is know as the superparamagnetic limit in size. This phenomena describes what happens to a ferromagnetic when the particle size decreases below a certain value, namely due to thermal fluctuations the materials can no longer retain its ferromagnetism and it becomes effectively a paramagnet. To counteract this, materials with a stronger tendency to retain their ferromagnetism must be utilized. The intrinsic property which measures this tendency is the magneto-crystalline anisotropy of the magnet. Of particular interest in this regard are the high anisotropy materials CoPt and FePt. These alloys have the L10 ordered structure which is a FCC derivative structure with tetragonal symmetry (Space Group P4/mmm, Pearson Symbol tP2, prototype CuAu I). In these materials there are structural domains (variants), translational domains (anti-phase domains) and magnetic domains. The interplay between the development of these features will be an important aspect of our work. In our research we will examine how the magnetic domains develop in these high anisotropic magnetic materials. We will start with single crystal thin films of FePt and later move on to polycrystalline thin films with a variety of crystallographic textures. Of particular interest will be the use of applied fields to control the distribution of the domains and therefore to control the way in which the material responds to magnetic fields. We will explore these interesting features both experimentally and by means of computer simulation.