Magnetization-induced Optical Second Harmonic Generation Research Articles

Anisotropy of magnetization-induced surface optical second harmonic generation from Co doped rutile TiO 2

We have investigated the surface magnetization anisotropy of 5 at% Co doped rutile TiO 2 (1 1 0) using magnetization-induced optical second harmonic generation (MSHG) in the longitudinal Kerr configuration with an incident beam angle of 4°. The MSH intensity pattern from the Co:TiO 2 without surface Co clusters showed two anisotropic lobes at the second harmonic photon energy of 2 ℏ ω = 3.13 eV . Since MSH intensity is proportional to surface magnetization, the result indicates an anisotropy of the surface magnetization of Co:rutile TiO 2 (1 1 0). This confirms the possibility that 5 at% Co:rutile TiO 2 (1 1 0) is a ferromagnetic dilute magnetic semiconductor at its surface, as proposed in our previous paper.

Magnetization‐induced optical second harmonic generation from the surface of Co‐doped rutile TiO2(110)

AbstractWe have investigated the surface magnetism of 5 at% Co‐doped rutile TiO2(110) using magnetization‐induced optical second harmonic generation (MSHG) in the longitudinal Kerr configuration with the incident beam angle of 4° . MSHG is observed at both 2ħω = 2.33 eV and 2ħω = 4.20 eV. MSH intensity showed a hysteresis as a function of the external magnetic field for the second harmonic photon energy of 2ħω = 4.20 eV at which the absorption length limits the MSHG origin to the surface layer of 10 nm due to the TiO2 bulk. Since 5 at% Co: TiO2(110) is judged to have no metallic Co near the top surface by XPS, the hysteresis is attributed to a carrier‐induced ferromagnetism at the surface of this material. Copyright © 2008 John Wiley & Sons, Ltd.

Quadratic effects in the nonlinear magneto-optical response of perovskite manganites studied with magnetization-induced second harmonic generation

The crystallographic and magnetic symmetry of centrosymmetric perovskite manganite epitaxial films is studied by magnetization-induced optical second harmonic generation (MSHG). It is shown that not only linear but also quadratic terms in the magnetization affect the nonlinear-optical response, the latter being even dominant for special geometries. In that case MSHG allows to simultaneously probe the crystallographic structure, the net magnetization (zero in demagnetized material), and magnetization squared (nonzero in demagnetized material).

Observation of periodic oscillations in magnetization-induced second harmonic generation at theMn∕Cointerface

Magnetization-induced optical second harmonic generation (MSHG) from exchange-biased $\mathrm{Mn}∕\mathrm{Co}$ thin films shows monolayer period oscillations at the $\mathrm{Mn}∕\mathrm{Co}$ interface as a function of Co thickness. Similar oscillations are found in the exchange bias $({H}_{E})$ and the coercivity $({H}_{C})$ in both the interface sensitive MSHG and the bulk sensitive magneto-optical Kerr effect, indicating that magnetic reversal in the Co bulk and at the $\mathrm{Mn}∕\mathrm{Co}$ interface is collinear. Assuming a linear relationship between the MSHG asymmetry and the magnetic moment, our results suggest that there is an enhancement of the interface net magnetic moment at the full monolayer regions.

Temperature dependence of magnetization-induced second harmonic generation at buried exchange-biased interfaces

We have investigated the temperature dependence of magnetization-induced optical second harmonic generation (MSHG) in the exchange-biased $\mathrm{Co}\mathrm{O}∕\mathrm{Cu}∕\mathrm{Fe}$ multilayer. Below the blocking temperature, there is a strong MSHG response from the $\mathrm{Co}\mathrm{O}∕\mathrm{Cu}$ interface which, for large exchange bias values, equals and even dominates the contribution of the ferromagnetic Fe interfaces. In a previous publication we showed that there is a correlation between exchange bias and the MSHG asymmetry. Here we demonstrate the relationship between the second harmonic Kerr rotation and exchange bias and, based on that, we offer additional evidence that pinned uncompensated spins are present beyond the range of Cu spacer thickness where a hysteresis loop shift is observed.

Component-resolved determination of the magnetization by magnetization-induced optical second-harmonic generation

We present a method for simultaneously measuring the two normalized in-plane magnetization components in magnetic thin films that allows for the reconstruction of the magnetization angle and the normalized value of the magnetization with subnanosecond temporal resolution. The calibrated method relies on the large contrast associated with magnetization-induced optical second-harmonic generation, permitting measurements with a dynamic range in excess of 25dB. Calibration is achieved by the determination of the relative magnitude and phase of the essential nonlinear optical tensor components, including those of a magneto-optic origin. Ellipsometric determination of the polarization of the second-harmonic signal, when the magnetization is saturated along four in-plane Cartesian directions, is sufficient to determine the second-order nonlinear tensor components. These four directions represent the two saturated states along the longitudinal and transverse directions of the magnetization, respectively. The tensor components are subsequently used to uniquely determine the in-plane magnetization amplitude and direction.

Direct Observation of Exchange Bias Related Uncompensated Spins at theCoO/CuInterface

Magnetization-induced optical second harmonic generation (MSHG) from the exchange-biased CoO/Cu-(X)/Fe multilayer shows the presence of pinned uncompensated spins at the CoO/Cu interface. For increasing Cu spacer thickness, the exchange bias measured via the hysteresis loop shift diminishes and disappears at X = 3.5 nm, while the MSHG signal still shows a strong magnetic contribution from the CoO interface. This indicates that the magnetic interaction between Fe and CoO layers is sufficiently strong to induce order in the antiferromagnetic layer even at a spacer thickness for which there is no observable hysteresis loop shift.

Large-angle magnetization dynamics investigated by vector-resolved magnetization-induced optical second-harmonic generation

We examine the relationship between nonlinear magnetic responses and the change in the Gilbert damping parameter α for patterned and unpatterned thin Permalloy films when subjected to pulsed magnetic fields. An improved magnetization-vector-resolved technique utilizing magnetization-induced optical second-harmonic generation was used to measure magnetization dynamics after pulsed-field excitation. The magnetization excitations were achieved with pulsed fields aligned parallel to the hard axis of thin permalloy (Ni80Fe20) films while a dc bias field is applied along the easy axis. At low bias fields, α was inversely related to the bias field, but there was no significant reduction in the absolute value of the magnetization, as might be expected if there was significant spin-wave generation during the damping process. We discuss the discrepancies between data obtained by ferromagnetic resonance, whereby spin-wave generation is prevalent, and pulsed-field studies, with the conclusion that fundamental differences between the two techniques for the excitation of the ferromagnetic spin system might explain the different proclivities toward spin-wave generation manifest in these two experimental methods.

Strong surface state effects in nonlinear magneto-optical response of Ni(110).

Spectroscopic magnetization-induced optical second harmonic generation (MSHG) measurements from a clean Ni(110) surface reveal strong resonance effects near 2.7 eV that can be attributed to the presence of an empty surface state. The good agreement with model calculations shows the potential of MSHG to probe spin-polarized interface band structures.

Nonlinear magneto-optical imaging of interface magnetic structures

We report the development of a new magnetic imaging technique: nonlinear magneto-optical microscopy. Magnetization-induced optical second harmonic generation (MSHG) is used to image the domain structure in ultrathin Pt/CoNi/Pt and Au/Co/Au/Fe/GaAs films. Due to both very high magneto optical contrast and enhanced interface sensitivity, fine details of magnetization several on film interfaces become visible with the MSHG imaging that are not detectable by usual magneto-optics.

Nonlinear and linear Kerr studies of [formula omitted] multilayers

Magnetization induced optical second harmonic generation (MSHG) in combination with the magneto-optical Kerr effect (MOKE) was used to study thin Co films and Cu Co multilayers of thicknesses between 1 and 20 monolayers (ML) grown on a Cu(001) substrate. From the different dependence of MSHG and MOKE on Co film thickness we get direct information about the interface sensitivity of MSHG. Modifying the vacuum Co interface by gas adsorption yields the relative contributions of the vacuum Co and the Co Cu(001)- substrate interfaces. Both MSHG and MOKE data can be accurately described by a multiple reflection model.

Magnetization-induced optical second-harmonic generation from magnetic multilayers

The optical second-harmonic intensity generated by magnetic multilayers appears to depend strongly on the magnetization. Combining interface and magnetic sensitivity, magnetization-induced optical second-harmonic generation provides a unique tool to study magnetic interface properties. The underlying theoretical analysis is given and illustrated with an example and experiments on Co/Au multilayers.