Influence of magnetic interaction and particle length on MP tape noise

Some noise characters were measured for MP tapes of different particle size at different packing fraction which is controlled by diluting with nonmagnetic powder, α-Fe₂O₃. We employed δM as an indication of magnetic interaction. δM reduced with decreasing packing fraction. The reduction was much larger for the 0.10 μm particle than the 0.25 μm particle. This result suggests that the 0.10 μm particle and the 0.25 μm particle have different structures, which was confirmed by using a dark-field microscope. The tape using the 0.10 μm particle had a higher AC erase noise than DC erase noise because of high magnetization and high coercive force. Conversely, AC erase noise was lower than DC erase noise for the 0.25 μm particle. AC erase noise could be decreased by diluting with a nonmagnetic powder for the 0.10 μm particle. The shoulder noise of the signal was also decreased by diluting and the reduction was twice that of output reduction. A plausible explanation for the noise reduction is the clearness of the border on the recording pattern, and this was confirmed with MFM. From the result of angular dependence of H_c, it is suggested that the magnetic reversal mode changes with packing fraction for the 0.10 μm particle, and this conversion may affect tape noise characteristics