Magnetization-induced-second-harmonic generation from surfaces and interfaces

Abstract

Magnetization-induced effe_ct.s in the nonlinear optical response of magnetic media, such as magnetizationinduced-second-harmonic generation (MSHG), led to very strong and novel non linear magneto-optical effects that appear to be very sensitive to magnetic interface properties. This surface-interface sensitivity ofMSHG, in combination with the very large magneto-optical effects, has led to a fast development of this technique over the past decade. On the one hand, an extreme sensitivity of MSHG to the electronic and magnetic structure of clean surfaces has been successfully demonstrated. On the other hand, the penetration depth of light allows one to use this sensitivity to study buried interfaces in multilayer systems. Further experimental developments of the MSHG technique, such as space and time t·esolution as well as magnetization-sensitive-sumfrequency generation, appear to be promising as well.

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

“…(1) are expressed using the simplified notation χ ij k = ij k and χ ij kL = ij kL, respectively, where the upper-case subscript L, describing the magnetization direction, is introduced to avoid potential confusion with unrelated quadrupolar susceptibility tensor components. 7 The interface formed by the pseudomorphic deposition of a magnetic species on a vicinal surface, consisting of well-ordered 1 m atomic steps separated by higher-symmetry surface terraces, possesses overall 1 m symmetry. If the surface normal of the interface is in the z direction, the normal to the single mirror plane is in the y direction, and the magnetization is in the x direction, then the dependence of the y-polarized NI MSHG intensity on ϕ, the angle between the input polarization field and the x direction, is given by 10 I y (2ω,ϕ, ± M X ) ∝ |yxy sin 2ϕ ± {yxxX cos 2 ϕ…”

“…Photon-inphoton-out techniques ("epioptics" 5,6 ), such as optical secondharmonic generation (SHG), which use symmetry to extract the optical response of the interface from the normally dominant bulk response, allow the buried interfacial structure of centrosymmetric materials to be probed through thin capping layers, and magnetic SHG (MSHG) extends this to magnetic interfaces. However, the vast majority of magnetic thin-film systems that have been studied so far are of high surface and interface symmetry, 7 because of the general complexity of the MSHG response and the often poor signal-to-noise ratio (SNR). 8 Lower symmetry systems, which may have multiple magnetic regions, have many tensor components that may contribute to the MSHG intensity, making interpretation particularly difficult.…”

Magnetic second harmonic generation at the Co2MnSi∕AlOx interface

“…The four combinations of the incident and collected optical polarization states probe different components of the nonlinear optical susceptibility tensor that describes the MSHG. 3,12 From here on, we use the notation s, p to refer to incident fundamental polarization, and S, P to refer to collected second harmonic polarization. The collinear 800 and 400 nm components of the reflected beam were spatially separated using Brewster prisms, and the 400 nm light was detected by a digital photon counting system, with background count rate of 20 counts/ s. For cubic crystals, in the electric dipole approximation, SHG is only allowed at the interfaces where the bulk inversion symmetry is broken.…”

“…For magnetic crystals, timereversal symmetry is also broken. 12,13 The second harmonic polarization is related to the incident optical electric field and interface magnetization by…”

“…3͑e͒ and 3͑f͔͒ shows the MSHG asymmetry, A = ͓͑I͑+M͒ − I͑−M͒͒ / ͑I͑+M͒ + I͑−M͔͒͒, which has been suggested to be a more reliable measure of the magnetic contribution to the SHG yield. 12 In the final panel ͓Fig. 3͑g͔͒, we plot the difference in the MSHG asymmetry for M parallel to the ͓100͔ and ͓110͔ axes, which we refer to as the MSHG anisotropy, defined by A͓͑110͔͒ − A͓͑100͔͒.…”