Effect of sputter-etching polymer substrates on the magneto-optical properties of ultrathin Co/Pt multilayers

Ultrathin Co/Pt multilayers deposited directly on polymer substrates displayed poorer Kerr hysteresis loops than multilayers deposited on glass substrates. However, sputter-etching the polymer substrates with oxygen gas produced a square Kerr hysteresis loop. Analysis of the liquid-solid contact angle at the substrate surface confirmed that the low surface free energy of the substrate gives rise to poor magneto-optical (MO) properties of the deposited Co/Pt film. The MO properties are improved by etching. This is the result of an increase in the surface free energy, which is probably related to a chemical reaction involving oxygen atoms and not due to a change in the surface morphology. Higher surface free energy or better wetting of the surface made possible by etching probably brings about better nucleation of the deposited atoms in the initial stage of film growth and improves the crystalline quality of film, resulting in an improvement in the MO properties.