Calculations of Stable Domain Radii Produced by Thermomagnetic Writing

Abstract

Calculations are performed to determine the stable radius of a cylindrically symmetric domain nucleated in magneto-optical films during thermomagnetic writing with a laser beam. A critical bound on domain size is calculated which determines whether or not a domain of given radius, once nucleated, will be stable. The analysis shows that for a ferromagnetic material such as MnAlGe, the domain dimensions can grow beyond the local region of material that is heated above the Curie temperature. For ferrimagnetic thin films having a compensation point T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">comp</inf> , stability depends on the difference between ambient and compensation temperatures, ΔT = T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</inf> − T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">comp</inf> . With ΔT ≈ 0, wall energy dominates and the critical radius can be calculated from R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> = σ/(2MH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> ).