MnBi Thin Films: Physical Properties and Memory Applications

Abstract

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.