L. Carroll

Extracting the hysteresis loops of magnetic interfaces from optical second-harmonic intensity measurements

Surface- and interface-sensitive optical techniques, such as optical second-harmonic generation (SHG), allow the buried interfacial structure of centrosymmetric materials to be explored through thin capping layers, and magnetic SHG (MSHG) extends this to magnetic interfaces. However, the variation of the MSHG intensity with magnetic field does not measure hysteresis loops directly, because the loops are displaced by an amount dependent on the crystallographic response and its phase difference with respect to the magnetic response, and also because there is a quadratic magnetization contribution to the SH intensity that may be significant. Two new procedures are reported for extracting hysteresis loops directly from the MSHG intensity. The first is applicable to all magnetic interfaces, including exchange-biased structures, where the saturation magnetization for positive and negative magnetic fields is equal and opposite. The second applies to all centrosymmetric hysteresis loops. These procedures correct for the quadratic response, allowing experimental geometries to be chosen that maximize the magnetic contribution, thus improving the signal-to-noise ratio and the sensitivity of the technique.

Temperature-dependent magnetic second-harmonic generation from Fe nanostructures grown on vicinal W(110)

Temperature-dependent magnetic second-harmonic generation (MSHG) at normal incidence (NI) is used to determine magnetization curves from Au-capped ultrathin Fe nanostructures grown on a vicinal W(110) substrate. Aligned magnetic nanostructures grown on low-symmetry interfaces are generally inhomogeneous, with different magnetic species, such as terrace and step atoms, contributing to the overall magnetic response from the interfacial regions. A phenomenological model of NI MSHG intensity and contrast at magnetic interfaces of 1 m symmetry is used to extract the magnetization information. Two characteristic temperatures are identified for both 0.75 and 2.0 monolayers of Fe, and it is proposed that the increased sensitivity of SHG to step atoms, compared to linear optical techniques, allows the contribution of boundary atoms to the spin block response to be directly detected at lower temperatures. The behavior of boundary spins such as these is expected to be important for atomic-scale magnetic structures.