Observation of Large Kerr Angles in the Nonlinear Optical Response from Magnetic Multilayers

Abstract

We have observed a longitudinal nonlinear (second-harmonic) Kerr rotation up to 22° for an Fe(2 nm)/Cr(2 nm) multilayer on an S i0 2 substrate that shows a linear Kerr rotation o f only a few hundreths o f a degree. The latter value excludes any linearly induced mechanism and confirms the interface sensitivity o f this nonlinear Kerr technique. The enormous enhancement is shown to be in good agreement with recent predictions, based on spin dependent band structure calculations. The local optical field effects are shown to play an important role for the additional enhancements for such multilayers on a substrate. Besides their fundamental interest, these systems are also interesting for their potential in practical applications.One o f the most widely used techniques to study the magnetic properties o f magnetic thin films is the magneto optical Kerr effect (MOKE). In addition, MOKE is widely used for magnetic imaging. In this context, and also to study very thin films, large Kerr rotation angles are favorable.Recently, it has been pointed out by Pustogowa, Hiibner, and Bennemann that in nonlinear optical secondharmonic generation (SHG) from magnetic materials enormous enhancements of the Kerr angles can be expected [ In this paper we present experimental nonlinear Kerr data for a magnetic Fe/Cr multilayer in the longitudinal configuration. We show that extremely large nonlinear Kerr angles are found for this very thin magnetic layer, for which the linear magneto-optical Kerr rotation is (vanishingly) small. Experimentally is found to be largest for the ^-polarized input, with values between 5° and 2 2° for angles of incidence between 15° and 70°. For the p -input configuration we measure a rotation angle of 1° to 5° for incident angles between 15° and 7 0°. This is shown to be in good agreement with the results of band structure calculations on (bulk) Fe surfaces by Pustogowa, Hiibner, and Bennemann [9]. We will also show how the substrate, through local field effects, can influence the magnitude of the observed 4>k\The sample consisted of a thin Fe film (thickness 2 nm), covered with a 2 nm Cr film deposited by rf diode and dc magnetron sputtering, respectively. As a substrate we used a (100) silicon wafer, with a thermal oxide layer of about 525 nm. The substrate was on a rotating table, which moved with a velocity of 0 .9 6 and 3 .9 7 m /m in underneath the Fe and Cr targets, respectively. Both targets were equipped with screens for getting uniformity of the layer thickness better than 1%. The base pressure was 2 X 10~7 Torr and the Ar pressure was 5 mTorr. For the second harmonic experiments we used the 7 7 0 nm output of a mode-locked (8 0 MHz) Ti-sapphire laser. The pulse width was 7 0 fs and the input power was 100 mW focused on a spot diameter of 100 jmm. The experiments were done in the longitudinal configuration, i.e., the magnetization M was in the plane of the sample and in the optical plane of incidence (see inset, Fig. 1). Figure 1 shows the polarization dependence of the SH signal for an ^-polariz...

Domain structures during magnetization reversal in exchange-biased layers

“…Indeed, the MSHG intensity in the P in S out polarization combination is zero unless there is a component of M in the plane of incidence. 12 The hysteresis loop measured in that configuration ͑see Fig. 3͒ clearly shows an increase of MSHG intensity corresponding to the magnetization tilt away from the field axis.…”

Nonlinear Magneto-Optics of Magnetic Thin Films

“…One sample consisted of a thin Fe film (thickness 2 nm), covered with a 2nm Cr film deposited by Rf-diode and DC magnetron sputtering, respectively (for details on sample preparation see [8]. The experiments were done in the longitudinal configuration.…”

Interdiffusion and magnetism of the Co/Rh interface studied by magnetization induced second harmonic generation

“…[4][5][6] These effects are due to the simultaneous breaking of inversion symmetry ͑at interfaces͒ and time-reversal symmetry 7 ͑by the magnetization͒.…”