Physical and Magnetic Properties of Magnetic Nanoparticle Arrays

Using Scanning Electron Microscope (SEM) , Atomic Force Microscope (AFM) and Vibrating Sample Magnetometer (VSM) I studied magnetic-field directed self-assembly of magnetic nanoparticles into patterned arrays on the surface of perpendicular magnetic recording media. A controllable machine was used to coat super paramagnetic nano particles onto the surface of perpendicular recording media for different time intervals. Self assembled nano particles on the surface of the media, were transferred to a polymer layer to observe physical properties. Results from imaging shows that the average width and height of arrays is increasing as a function of time. Width of arrays varies with assembly time from 149nm at 5 minutes to 525nm at 120 minutes. Similarly, height changes from 13nm at 5 minutes to 37nm at 120 minutes. Therefore the pattern aspect ratio changes from 10:1 at 5 minutes to 14:1 at 120 minutes. For large widths compared with pattern spacing, interactions appear as a slope change in VSM hysteresis loops. Results suggests that there is a significant slope change as the coating time increases and there is a local magnetic particle-particle interaction