Optimizing the magnetic contrast in the optical second‐harmonic response of capped magnetic nanostructures grown on vicinal surfaces

Abstract

Measuring the magnetic response from buried interfaces using magnetic second harmonic generation (MSHG) is difficult due to the general complexity of the response and the often poor signal‐to‐noise ratio (SNR). Low dimensional nanostructures grown by self‐assembly at aligned atomic steps, which typically exhibit only 1m symmetry, are particularly challenging. Near‐normal incidence SHG simplifies the crystallographic nonlinear response from such low symmetry systems by effectively excluding z‐dependent tensor components. A phenomenology is developed to show that, for 1m vicinal systems, careful choices of input and output polarization and experimental geometry can produce enhanced magnetic contrast and thus allow magnetic hysteresis loops with improved SNR to be extracted. An example of the application of this new MSHG approach to Fe monolayers grown on vicinal W(110), capped by 16 nm of Au, is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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

“…The contrast plots contain cusp-like turning points at the input polarization angles of ϕ c and ϕ s , and symmetry-related positions. It has been shown that δ can be deduced from these cusps [17]. Also, measuring the y-polarized NI MSHG intensity near ϕ c (≈0 • ) or ϕ s (≈90 • ) reduces the odd contribution effectively to a single tensor component, simplifying the interpretation of results.…”

“…It has been shown that, through careful choice of sample alignment with respect to input polarization selection and the direction of applied magnetic field, it is possible to measure a NI MSHG intensity from 1m magnetic interfaces containing just one contributory crystallographic tensor component (even with respect to reversal of the magnetization direction) and two magnetic (odd) tensor components [16]. It was recently demonstrated that, with this geometry, the relative magnitude and phase of the even and odd components can be determined [17].…”

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

“…However, simulations confirm that such measurements maximize the probability of detecting contributions from different magnetic components. 9,10 It is also important to note that, in contrast to the magnetic terms, the crystallographic yxy (n) terms can only originate at the steps and edges, as the terrace contribution is forbidden by its 2 mm symmetry.…”

“…We have shown recently that normal incidence (NI) geometry, which drastically reduces the number of tensor components contributing to the signal, allows useful information to be extracted from the MSHG response of aligned magnetic nanostructures grown on low-symmetry interfaces. 9,10 Although NI geometry reduces the size of the SH response significantly, reasonable SNRs using unamplified fs pulses were obtained from submonolayer (ML) amounts of Fe deposited on a vicinal W(110) substrate and capped by 16 nm of Au.…”

“…24 It has been demonstrated that, with this geometry, the relative magnitude and relative phase of the even and odd components can be determined. 9 Low-symmetry magnetic interfaces are inhomogeneous, containing two or more regions where the same magnetic species is found with a different number of magnetic and nonmagnetic nearest neighbors. Since the magnetic properties of an interface are known to depend sensitively on nearest-neighbor number and type, 12 a full description of NI MSHG from an inhomogeneous interface must account for the contributions made by components from the different regions.…”