Magnetic second-harmonic generation from the terraces and steps of aligned magneticnanostructures grown on low symmetry interfaces

Abstract

Aligned magnetic nanostructures grown on low symmetry interfaces are generallyinhomogeneous, with different magnetic species, such as terrace and step atoms,contributing to the overall magnetic response from the interfacial regions.It is shown that the presence of different magnetic regions can be detectedby means of normal incidence (NI) magnetic second-harmonic generation(MSHG). A phenomenological model of NI MSHG at magnetic interfaces of1m symmetry is developed and a methodology is described for optimizing the signal-to-noiseratio of extracted hysteresis curves by adjusting the input polarization angle. Quadraticterms in the magnetization are properly accounted for, using recently published formulae.It is shown that, where more than one magnetic region is present, the shape of theextracted hysteresis curve, which contains contributions from the different magneticregions, varies with the input polarization angle. The new approach is used to determinehysteresis loops from the various magnetic regions of Au-capped ultrathin Fe filmsgrown on a vicinal W(110) substrate. The results for 0.75 ML Fe coverage areof particular interest, revealing distinct contributions from terrace and step Featoms. This experimental procedure and phenomenology opens up low symmetrymagnetic interfaces and aligned nanostructures to characterization by means ofMSHG.