Magnetic second-harmonic generation from interfaces and nanostructures

Abstract

Magneto-optic techniques provide non-contact and non-destructive characterization of magnetic materials. This includes embedded magnetic nanostructures, which are accessible due to the large penetration depth of optical radiation. The linear magneto-optic Kerr effect is widely used in the growth and characterization of ultra-thin magnetic films and can show monolayer sensitivity. Nonlinear magnetic second-harmonic generation (MSHG) is a more difficult and expensive technique but, uniquely, can measure the surface and interface magnetism of centrosymmetric magnetic films with sub-monolayer sensitivity. MSHG is briefly reviewed and examples from high symmetry interfaces and nanostructures described. Low symmetry structures are more difficult to characterize, however, because of the large number of tensor components that may contribute to the signal. An important class of low symmetry systems exploits vicinal substrates to grow aligned magnetic nanostructures by self-organization. These structures have a high proportion of magnetic step or edge atoms relative to the terrace atoms, and the overall magnetic response is expected to contain significant contributions from these different magnetic regions. It is shown that contributions from these different regions can be identified using normal incidence (NI) MSHG. This new approach is used to determine hysteresis loops from Au-capped Fe monolayers grown on a vicinal W(1 1 0) substrate. Temperature-dependent studies of the MSHG contrast also allow Curie temperatures to be determined. This experimental procedure and phenomenology opens up low symmetry magnetic interfaces and aligned nanostructures to characterization by MSHG.