Study of advanced thin film media for high density magnetic recording

Longitudinal thin film media are the leading candidates for future ultra-high density recording. Future recording media must have high squareness of the hysteresis loop, low noise (both transition noise and track edge noise), and good track edge performance to reach targeted 10 Gbit/in{dollar}sp2{dollar} recording densities. In this thesis, magnetic hysteresis and the recording properties of thin film media with advanced microstructure such as bicrystal film, nanocrystalline film and multilayer magnetic thin films are studied using micromagnetic modeling and spin-stand tester noise measurement.; In the micromagnetic model used in this thesis, the magnetic thin film is represented by a 2D array of closely packed hexagons, each corresponding to a single domain magnetic grain with uni-axial crystalline anisotropy. Long range magnetostatic interaction and nearest neighbor exchange coupling are considered. The magnetization state of each grain is determined by solving the Landau-Lifshitz equation. Bicrystal film is modeled by randomly assigning the crystalline easy axis of the grains in two orthogonal directions. Calculations show high squareness of the hysteresis loop in the diagonal direction between the two crystalline easy axes. Bicrystal film also exhibits low medium noise and good track edge over-write properties. Magnetic thin films with nanocrystal subgrain structure are also modeled. The model was modified such that each normal grain contains seven subgrains. It is found that small but non-zero exchange coupling between the normal grain boundaries is the key to achieving high coercive squareness. Reducing the exchange coupling between the subgrains results in lower media noise.; Time domain spin-stand noise measurements were performed to study the track edge noise reduction effect in multilayer thin film media. A large memory digitizer was used to capture the readback voltage waveform of the periodically written dibit sequence. Multiple readings were used to average out electronic noise. The variance of the dipulses in the data sequence is the measured medium noise. The magnetostatic interaction between the adjacent magnetic layers yields random charge cancellations in the side written band, and results in track edge noise reduction.