MnBi Thin Films: Physical Properties and Memory Applications

Thin films of MnBi possess many unusual physical properties and are particularly suitable for memory applications using laser Curie-point writing and magneto-optical readout. Films prepared on mica substrates have the easy direction of magnetization perpendicular to the film plane. They typically have a specific Faraday rotation of 5×105 deg/cm, and an absorption coefficient of 3.8×105 cm−1 for 6328 Å wavelength, permitting a readout rate of 109 bits/sec at 1 mW laser power level using available detectors. Curie-point writing and erasing of a spot a few microns in diameter in a 1000 Å thick film with a 4 μsec pulse from a 13 mW Gaussian laser beam have been achieved. For a 106 bits/cm2 packing density, heating at adjacent spots is negligible. Calculations show that the writing magnetic field can be reduced to less than 10 Oe by using a memory plane consisting of discrete squares of MnBi. Analytical and experimental results as well as memory design considerations are presented.