Theory for Spin-Polarized Oscillations in Nonlinear Optics due to Quantum Well States

Abstract

Using an electronic tight-binding theory we calculate the nonlinear magneto-optical response from an x-Cu/1Fe/Cu(001) film as a function of frequency and Cu overlayer thickness (x=3. . .25). We find very strong spinpolarized quantum well oscillations in the nonlinear magneto-optical Kerr effect (NOLIMOKE). These are enhanced by the large density of Fe d states close to the Fermi level acting as intermediate states for frequency doubling.In good agreement with experiment we find two oscillation periods of 6-7 and 11 monolayers the latter being more pronounced. Typeset using REVT E X 1The magnetism of low-dimensional metallic structures such as surfaces, thin films, and multilayer sandwiches has recently become an exciting new field of research and applications [1]. In particular, thin magnetic films and multilayers exhibit a rich variety of properties not previously found in bulk magnetism such as enhanced or reduced moments [2], oscillatory exchange coupling through nonmagnetic spacers [3][4][5], giant magnetoresistance [6,7], and the reorientation of the magnetic easy axis upon thickness and temperature variation [8][9][10][11]. Especially the observation of spin-polarized quantum well states (QWS) [12][13][14][15] in Cu/Co (001) has attracted a great deal of attention. It has become clear that quantum well states are indeed responsible for the important oscillatory behavior of the exchange coupling of ferromagnetic thin films via nonmagnetic spacers [16,17]. Presently mainly photoemission (PE) and inverse photoemission (IPE) [12][13][14][15] have been used to identify QWS effects. Very recently a possible connection between thickness dependent changes in NOLIMOKE and QWS [18] has been proposed.It is the goal of this Letter to show that also nonlinear optics, in particular NOLIMOKE, is a new sensitive tool for studying QWS. We find very interesting structure in the NO-LIMOKE signal due to particular transitions in k-space. This is very remarkable since it indicates that NOLIMOKE is able to detect very sensitively k-dependent structures. This new effect seems to be of general interest for the physics of nonlinear optics and its relationship to the underlying electronic structure. Note, this is not the case for linear optics, since there the contribution of the Drude term of the dielectric function creates a strong background of transitions from all k-directions. Nonlinear optics, in contrast to linear op-

Nonlinear magneto-optics of Fe monolayers from first principles: Structural dependence and spin-orbit coupling strength

“…Also quantum well states which occur in sandwich structures could be resolved. This has been shown both experimentally [9,[37][38][39] and theoretically [7], by exploiting the fact that NOLIMOKE spectra reflect characteristic features of the bandstructures [40]. Recent work predicted that even the influence of surface antiferromagnetism on the optical signal can be resolved by the nonlinear magnetooptical Kerr-effect (NOLIMOKE) [8].…”

“…Therefore is has attracted considerable interest in recent research on interface magnetism [2][3][4][5][6][7][8][9][10]. In this paper we investigate the dependence of the nonlinear magneto-optical Kerr-spectra and their microscopic origin [11] the spin-orbit coupling (SOC) and the magnetic moment -of Fe monolayers on structural changes.…”

Symmetry analysis of second-harmonic generation at surfaces of antiferromagnets

“…• , pronounced spin polarized quantum well state oscillations [11,12], magnetic contrasts close to 100%) [13,14]. An example of ferromagnetic effects measurable only by SHG deals with the existence of surface magnetism in very thin films of Fe/Cu(001) and is given in Ref.…”

Nonlinear Magneto-Optical Response from Quantum Well States in Noble Metals: Double Period and Interface Localization

“…Considering the recent calculations predicting a possible interface localization of the QWS-induced density o f states [13] and the enhanced k-space selectivity [14], MSHG can be expected to be a powerful tool in studying the properties o f such QWS. In addition, the three-photon nature of MSHG could give rise to new (compared with MOKE) oscillatory periods appearing as a function of the film thickness [14].…”