NEUTRON ELLIPSOMETRY

We discuss the similarities which exist between the reflection of neutrons from ferromagnetic media and the reflection of light from media rendered gyrotropic by the application of a magnetic field, and show that the vector character of the neutron polarisation can be fully exploited in spin-analysed neutron reflection measurements (termed 'neutron ellipsometry' because of the similarity to optical ellipsometry) to give valuable magnetometric information for ultrathin films and multilayers, and with certain advantages over conventional polarised neutron reflection measurements. We show that for the case of a single ultrathin magnetic layer with uniform magnetisation, the component of the in-plane magnetisation perpendicular to the incident neutron polarisation determines both the spin conserving and spin flipping reflectivities in the region of total reflection, while a more complex regime obtains in the partially reflecting region. Making neutron ellipsometric measurements in both reflection regions thus allows the magnitude and orientation of the in-plane magnetisation vector to be directly determined. This is illustrated by numerical calculations for a single ultrathin iron layer supported by a silver substrate and with a silver cap. © 1993