Thermal activated variation in the ordered structures in magnetic fluids films

A hexagonal ordered structure of magnetic columns is achieved in a highly homogeneous magnetic fluid film under an external magnetic field perpendicular to the film surface. At a fixed temperature, the magnetic columns are stable. When the temperature rises, the columns remain unchanged initially, and then some of them disappear as the temperature exceeds a critical value. Furthermore, all columns disappear when the temperature is further raised. The column disappearance was due to the dispersion of column particles into the liquid at a higher temperature. The critical temperature, at which the column particles start to melt, was found to increase under a stronger magnetic field. The relationships between the critical temperature and the fluid concentration, as well as the film thickness, are investigated. Thus, the role of temperature in the stability of ordered structures in the magnetic fluid film is clarified.