Observations of repeated Curie-point writing effects on MnBi films

Curie-point writing on MnBi films with a focused laser beam provides a means of substantially improving the packing density of magnetic recording. The MnBi film, however, has two crystallographic phases with different Curie temperatures. This causes the laser power requirement for writing to become a function of the operating history of the data bit location. Fortunately, the normal room-temperature phase has a higher laser power requirement than the quenched or mixed phase compositions. Therefore, the initial conditions for writing are suffieient for any subsequent condition. The time constants for these trasformations and the resulting optical memory characteristics have been observed and measured. Long-term operational lifetime has also been examined. The results show that when the laser writing power is 10% above writing threshold, the readout signal remains constant indefinitely; whereas when the writing laser power is more than 20% above the threshold value, continual degradation occurs. These experiments further confirm MnBi as a practical magneto-optic storage medium.