Final Report Summary - MAGDOT (Bridging atomistic to continuum - multiscale investigation of self-assembling magnetic dots during Epitaxil growth)
The need for novel materials has driven modern solid state physics and technology toward structures that exist on a very small scale. The recent development of nanometer-size heterostructures, such as nano-wires and nano-dots, has proven the potential for their enormous advantages over traditional materials, despite associated technological challenges. Thus, the nanoscale structures are the focus of novel material development and computational approaches that have taken a key role in the exploration of their unique properties and development. The success in this field shown for electronic and optoelectronic applications provides the basis for our proposal to computationally study the nanoscale self-assembly of magnetic dots during heteroepitaxy.
The ultimate goal of the project was to develop an understanding of the important materials issues governing nanoscale self-assembly, and to develop models that enable the first principles design of novel super-high density magnetic storage materials, such as FeP t and CoPt. Current magnetic recording technology is bounded by the superparamagnetic limit which sets an upper limit for recording density on conventional media, which will be reached in the near future. One approach to circumvent superparamagnetism was to create a medium where the number of grains needed to store one bit can significantly reduced and ultimately one bit of information can be stored on a single nano-sized island. Such small structures drastically increase storage density beyond that achievable by traditional means. Combined with an enhanced magnetic anisotropy by exploring specific alloys, and new writing concepts magnetic islands could be as small as 5 nm. Potentially they represent an increase in density by a factor of 100 over traditional thin film magnetic media.
The major challenge in creating such materials is that a regular pattern of nano-sized magnetic dots is required. For cost-effective processing, some degree of self-assembly was essential. The understanding of the fundamental phenomena occurring during heteroepitaxy using computational approaches facilitated the future development of processing methods that yield the desired structures. We elaborated an integrated approach to examine the self-assembly of nanoscale structures by joining forces of computational experts from the European Community and the United States, spanning the atomistic to the continuum scales.
The work involved ab initio calculations of surface energies, surface stress, and surface diffusion coefficients, as well as statistical mechanics, mesoscopic and continuum calculations of the evolution of nanostructural morphology and composition during deposition and annealing, resulting in self-assembly. By parameter passing, each effort fed into the other, as the information at the smaller scale will be employed in the larger scale calculations, enabling us to bridge a wide range of length and time scales. Using this approach, we addressed questions such as how the interplay between kinetic and thermodynamic effects leads to nanostructure formation and what the controlling factors of the spatial and size distributions are. Answers to these questions are not only of fundamental interest but also allow us to provide the integrated computational models needed to produce large scale self-organised arrays of magnetic dots.
To fulfil these specific tasks we combined modern mathematical tools, like phase-field models, homogenisation techniques and asympthotic expansion with state-of-the-art computational methods, such as multigrid solvers, adaptive and composite finite elements, parallel kinetic Monte Carlo simulation and intensive experimental validation on model systems of Fe/Mo and Fe/W.
The ultimate goal of the project was to develop an understanding of the important materials issues governing nanoscale self-assembly, and to develop models that enable the first principles design of novel super-high density magnetic storage materials, such as FeP t and CoPt. Current magnetic recording technology is bounded by the superparamagnetic limit which sets an upper limit for recording density on conventional media, which will be reached in the near future. One approach to circumvent superparamagnetism was to create a medium where the number of grains needed to store one bit can significantly reduced and ultimately one bit of information can be stored on a single nano-sized island. Such small structures drastically increase storage density beyond that achievable by traditional means. Combined with an enhanced magnetic anisotropy by exploring specific alloys, and new writing concepts magnetic islands could be as small as 5 nm. Potentially they represent an increase in density by a factor of 100 over traditional thin film magnetic media.
The major challenge in creating such materials is that a regular pattern of nano-sized magnetic dots is required. For cost-effective processing, some degree of self-assembly was essential. The understanding of the fundamental phenomena occurring during heteroepitaxy using computational approaches facilitated the future development of processing methods that yield the desired structures. We elaborated an integrated approach to examine the self-assembly of nanoscale structures by joining forces of computational experts from the European Community and the United States, spanning the atomistic to the continuum scales.
The work involved ab initio calculations of surface energies, surface stress, and surface diffusion coefficients, as well as statistical mechanics, mesoscopic and continuum calculations of the evolution of nanostructural morphology and composition during deposition and annealing, resulting in self-assembly. By parameter passing, each effort fed into the other, as the information at the smaller scale will be employed in the larger scale calculations, enabling us to bridge a wide range of length and time scales. Using this approach, we addressed questions such as how the interplay between kinetic and thermodynamic effects leads to nanostructure formation and what the controlling factors of the spatial and size distributions are. Answers to these questions are not only of fundamental interest but also allow us to provide the integrated computational models needed to produce large scale self-organised arrays of magnetic dots.
To fulfil these specific tasks we combined modern mathematical tools, like phase-field models, homogenisation techniques and asympthotic expansion with state-of-the-art computational methods, such as multigrid solvers, adaptive and composite finite elements, parallel kinetic Monte Carlo simulation and intensive experimental validation on model systems of Fe/Mo and Fe/W.