This study mainly concerns applications of modeling and simulation for the purpose of playing a fundamental role in the systematic research of required properties materials. The model system is 50%Pt-50%Co binary thin film that is deposited and heat treated. The properties needed are excellent magnetic properties which will make the Pt-Co thin film as a good magnetic recording media.
Most requesting conditions of the system's state for the enhanced magnetic properties are the ordered structure and the grain size as small as possible.
The disordered structure transformed to ordered state during heating after deposition. However, heating induces grain growth which degrades magnetic properties of materials at the same time.
This study explored two possibilities to produce the desired structures for the good magnetic properties. First item was the possibility of forming ordered PtCo film without further heat-treatment. Second item was the possibility of limiting grain growth during heat-treatments.
MEAM parameters were obtained through optimizing process with experimentally reported lattice constants and heat of formations of Pt3Co, PtCo and PtCo3. As a test for those parameters calculation of order-disorder transition temperatures of Pt3Co, PtCo and PtCo3, and estimation of composition profiles of PtCo thin films with free surface (111) or (100) was performed. Calculated order-disorder transition temperature were within a range of maximum 120K from experimentally reported values. The forms of composition profiles were coincident to the experimentally reported forms, but segregating element at free surface was predicted to be Pt, which was contrary to the reported experimental result that showed the segregation of component Co at free surface.
MEAM parameters were proved to be reliable with regard to Pt-Co atomic mixing behavior and then parameters were used in Monte Carlo simulations. Two kinds of works were performed as followes.
First, the uses of pure metal substrates such as Ni, Cu, Au, Al, Ti, Zr, Ru, Pt, Co with free surface planes of (111), (100) or (0001) were investigated using MEAM (Modified Embedded Atom Method) potential energy and Monte Carlo simulation. Through anaysis of atom configurations produced by surface diffusion of Pt and Co atoms on the various pure metal substrates prospects for ordering during film growth were suggested. Ni(100), Cu(100), Au(111), Al(111) and Co(0001) were recommended, but cautions are needed because of oversimplified MEAM parameters for third elements such as Ni, Cu, Au, Ti, Zr, Ru and Al.
Second, for the purpose of constructing a base of simulation tool by predicting the exact function of grain growth size to real time, this study searched activation energy which can describe the behavior of mean size development in real time through 2 dimension grain growth simulation using Monte Carlo method. Development of structure in the thin film during deposition and grain growth simulation were also explored using 3-dimension modeling in order to observe the relation between 3-dimensional grain growth and 2-dimensional grain growth. 3-dimensional grain growth simulation showed the development of columnar structure in the thin film and confirmed that grain grew only in directions parallel to free surface, which justified 2-dimensional grain growth simulation of PtCo thin film. Based on this observation 2-dimensional grain growth simulation was performed to estimate optimum activation energy which defines the development scaling of mean size of grains` diameter as real time. Optimum activation energy was estimated as 0.5eV.atom(48.2kJ/mole).
