Magneto-optic Kerr effect hysteresis loop measurements on particulate recording media

A direct comparison between the surface and the bulk hysteretic behavior of particulate oxide recording media was made for the first time. The surface properties were measured using a magneto-optic Kerr effect apparatus operating in fields up to 10 kOe while the bulk hysteresis loops were measured with a vibrating sample magnetometer. Because of the very small Kerr rotations observed, typically an order of magnitude less than those of metal films, careful attention to experimental detail was required. Several different types of particulate recording media were measured. The surface coercivity was found to be about 10% higher than the bulk coercivity for some of the high energy tapes; however, it was virtually identical to the bulk coercivity in several other samples. A thorough discussion of the apparatus is given.