Yung-Huang Chang’s research while affiliated with National Yunlin University of Science and Technology and other places

This study explores cobalt–cerium (Co90Ce10) thin films deposited on silicon (Si) (100) and glass substrates via direct current (DC) magnetron sputtering, with thicknesses from 10 nanometer (nm) to 50 nm. Post-deposition annealing treatments, conducted from 100 °C to 300 °C, resulted in significant changes in surface roughness, surface energy, and magnetic domain size, demonstrating the potential to tune magnetic properties via thermal processing. The films exhibited hydrophilic behavior, with thinner films showing a stronger substrate effect, crucial for surface engineering in device fabrication. Increased film thickness reduced transmittance due to photon signal inhibition and light scattering, important for optimizing optical devices. Furthermore, the reduction in sheet resistance and resistivity with increasing thickness and heat treatment highlights the significance of these parameters in optimizing the electrical properties for practical applications.

The impact of film thickness and annealing temperature on the structural, electrical, magnetic, and mechanical properties of cobalt–iron–dysprosium (Co40Fe40Dy20 ) thin films deposited on Si(100) substrates have been investigated. X-ray diffraction (XRD) analysis confirmed the film's crystalline microstructure, featuring dysprosium oxide, Dy2O3(440), and cobalt oxide, Co2O3(422) and Co2O3(511), crystallographic phases. Surface energy measurements indicated a noticeable reduction in surface energy following annealing treatments, which could be ascribed to the alleviation of residual stress and enhanced atomic arrangement, resulting in a more stable film structure with reduced surface energy. The film exhibited a decreasing trend in hardness with increasing thickness, and film resistivity was significantly responsive to alterations in thickness and annealing temperature. Notably, the Co40Fe40Dy20 film demonstrated exceptional characteristics, featuring a high saturation magnetization (Ms) of 675 emu/cm3 and a low coercivity (Hc) of 9.5 Oe. Further analysis of magnetic domains and hysteresis loops revealed that larger and brighter domains were associated with higher Hc. To sum up, the surface roughness of CoFeDy films under various annealing temperatures played a pivotal role in shaping their magnetic, electrical, adhesive, and optical characteristics. An improved low-frequency alternating current magnetic susceptibility (χac) value was achieved by minimizing the pinning effect on domain walls through surface smoothing. Moreover, smoother surfaces displayed heightened carrier conductivity, resulting in a decrease in electrical resistance. On the whole, Co40Fe40Dy20 films exhibited outstanding soft magnetic properties, encompassing high saturation magnetization, low coercivity, exceptional mechanical attributes, and decreased surface energy.

In this study, we focused on depositing a target material, cobalt-iron-dysprosium (Co60Fe20Dy20), onto silicon (Si) (100) substrates with thickness varying from 10 nm to 50 nm through a direct-current (DC) magnetron sputtering technique. The subsequent step involved subjecting the samples to an hour-long annealing process in a vacuum annealing furnace at temperatures of 100°C, 200°C, and 300°C. To assess the elemental composition of the CoFeDy films, energy-dispersive X-ray spectroscopy (EDS) was employed. An observed trend indicated an increase in low-frequency alternating-current magnetic susceptibility (χac) with the increasing thickness. Remarkably, the CoFeDy films exhibited their peak χac following annealing at 300°C, with an optimal resonance frequency of 50 Hz. After annealing at 300°C, the CoFeDy film’s surface energy peaked at 50 nm. The magnetic, electrical, and adhesive properties of the CoFeDy films were notably influenced by surface roughness at different annealing temperatures. Atomic force microscopy (AFM) analysis revealed a gradual reduction in film roughness post-annealing, corresponding to smoother surfaces indicative of a weaker domain wall pinning effect, heightened carrier conductivity, and increased liquid spreading. Collectively, these outcomes contributed to diminished χac, reduced electrical resistance, and enhanced adhesion.

This study investigated the effects of varying film thicknesses and annealing temperatures on the surface roughness and magnetic domain structure of CoFeSm thin films. The results revealed that as the film thickness increased, both the crystalline size and surface roughness decreased, leading to a reduction in coercivity (Hc) and improved magnetic contrast performance. Energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the presence of cobalt (Co), iron (Fe), and samarium (Sm) within the thin films. Notably, the 40 nm Co40Fe40Sm20 thin film annealed at 200 °C exhibited lower sheet resistance (Rs) and resistivity (ρ), indicating higher conductivity and a relatively higher maximum magnetic susceptibility (χac) at 50 Hz. These findings suggest that these films are well suited for low-frequency magnetic components due to their increased spin sensitivity. The 40 nm Co40Fe40Sm20 thin film, subjected to annealing at 200 °C, displayed a distinct stripe domain structure characterized by prominently contrasting dark and bright patterns. It exhibited the lowest Hc and the highest saturation magnetization (Ms), leading to a significant improvement in their soft magnetic properties. It is proposed that the surface roughness of the CoFeSm thin films plays a crucial role in shaping the magnetic properties of these thin magnetic films.