M. Nývlt

Magneto-optical Kerr spectra of nickel

Abstract The complex polar Kerr effect spectra (Kerr rotation and Kerr ellipticity) of high-purity ferromagnetic nickel are reported in the spectral range 1.5–5.2 eV. Freshly evaporated high optical quality Ni films, 90 nm thick, magnetically saturated perpendicular to the film plane served as sample surfaces. New extended spectroscopic information has been obtained. The agreement with the published data is discussed.

Magneto-optical contribution of interfaces in ultrathin film Au/Co/Au structures

Abstract Magneto-optical (MO) polar Kerr rotation (PKR) and ellipticity (PKE) spectroscopic studies of Au(5 nm)/Co(0.4–1.8 nm)/Au(25 nm) ultrathin film sandwiches showed that the spectra can be represented as a sum of two components: one (nearly) linearly dependent plus one independent of the Co layer thickness, t Co . The two components were determined from the experiments on well defined sandwiches with stepped wedge Co layers after eliminating the MO contribution from the glass substrate and sandwiching the Au layers. Two effects responsible for the t Co -independent components: (1) spin polarization in the Au monolayers adjacent to Co and (2) roughness at AuCo interfaces were considered. The results of modelling and a comparison with MO spectra of gold suggest that latter effect is dominant.

Magneto-optic studies of Fe/Au multilayers

Abstract Magneto-optic (MO) polar and longitudinal Kerr spectroscopy is applied to rf sputtered Fe/Au multilayers characterized with SQUID magnetometry, ferromagnetic resonance and Lorentz microscopy. The main trends in MO spectra are explained by computer simulations using bulk data for Fe and Au. At lower Fe thickness the spectra show the Au plasma edge peak and the structure assigned to quantum well states. The reduced amplitudes and peak broadening with respect to the model in the measured spectra are explained as an effect of Au–Fe mixing at interfaces.

MO Kerr and Faraday studies of Au/Co ultrathin film structures

Abstract Magneto-optical (MO) polar Kerr and Faraday effect spectra in Au(5 nm) /Co/Au(25 nm) structures deposited by thermal evaporation in an ultrahigh-vacuum chamber on float glass substrates are reported. The Co layer thickness was varied only between 0.4 and 2 nm to preserve a perpendicular spin alignment under a moderate field. The experimental results are well explained with an electromagnetic wave model employing bulk optical constants of Co and Au and MO data of Co. Approximate formulae for a trilayer demonstrate the effects of ultrathin Co, Au buffer and overlayer thicknesses. Trends in the spectra when t Co varies from zero to 50 nm are illustrated.

Magneto-optical effects in a stack of magnetic multilayer-dielectric films

Abstract We studied individual magneto-optic (MO) contributions of [Tb/Fe] n multilayers in novel {[Tb/Fe] n /Si 3 N 4 } N structures displaying a considerable enhancement of Kerr and Faraday MO effects in red light. A strong sensitivity of individual MO contributions to photon energy is demonstrated and confirmed by an optical multilayer model. This allows us to probe selectively the magnetism of individual stacked multilayers.

Magneto-optical studies of ultrathin MBE grown Fe/Ag(001) wedges

Abstract Magneto-optical (MO) polar Kerr effect spectra of an ultrathin Fe wedge Cr/Ag/Fe/Ag structure grown by MBE on GaAs(001) substrate are reported. We demonstrate unusually strong changes of the MO response due to the presence of a Cr capping layer and its high sensitivity to the Ag/Fe interface structure. Magneto-optics stands as a powerful method for sample characterization in this case.

Magnetic and magneto-optical polar Kerr spectra studies in Ni/Au multilayers

Abstract Magnetic, magneto-optical (MO) and X-ray diffraction studies on Ni/Au multilayers deposited by e-beam evaporation onto glass substrates are reported. The individual layer thickness t Ni varied between 0.6 and 2.7 nm and t Au was fixed at 1.5 nm. The magnetic measurements at 5 K show negative surface anisotrophy and the absence of a dead layer. The most prominent feature in the MO Kerr spectra is a negative peak at 2.7 eV. The MO spectra are well explained by the theory using the bulk Ni and Au optical and MO data. The modelling indicates that the optical constants of Au change when the Au layer becomes ultrathin.

Magneto-optical enhancement in Pt/(Ni1−xCox) multilayers

Abstract Magneto-optical (MO) polar Kerr rotation (PKR) and ellipticity (PKE) spectra of Pt/(Ni 1− x ) multilayers with x = O, 0.3 and 1 nm prepared by evaporation under ultrahigh-vacuum conditions were studied. The thickness of the Pt layer was kept between 1.5 and 2 nm, and that of the ({Ni 1− x Co x }) alloy layer, t Ni 1− x Co x , was 0.45 and 1.4 nm Layers formed at the Pt—magnetic layer interfaces give rise to a surface-induced perpendicular magnetic anisotropy (PMA) and to an enhancement of PKR in the near-UV spectral region. Because the Curie temperature T c is close to 300 K for x = O a clear manifestation of these effects in the Ni/Pt system required cooling to low temperatures. The possibility to optimize the characteristics, like PMA, T C and the amplitude and position of the PKR peak in the spectra by proper choices of x , t Pt and t Pt and t Ni 1− x Co x makes Pt/(Ni 1− x Co x ) multilayers interesting for the realization of MO storage media capable of working in blue light.

Analytical expressions for polar magnetoptics in magnetic multilayers

This paper is a comprehensive study of different formalisms used to simulate polar magneto-optical (MO) effects in multilayers. A development of the 4 × 4 matrix calculation to first order in off-diagonal elements of the permittivity tensor gives original analytical expressions. They allow to express the MO effects in multilayers as a sum of contributions from individual layers. Each contribution consists of two components assigned to the interface and propagation effects. The explicit expressions for multilayers containing up to seven layers, together with those obtained in the frame of an ultrathin layer approximation, are shown to be useful both in a qualitative comprehension and in quantitative simulations of the experimental MO Kerr spectra of a wide variety of ultrathin magnetic structures. They can be used to separate the different contributions arising from the interfaces due to intermixing or spin polarization (including interface roughness) as well as to simulate magnetically coupled multilayers. As an example, the analytical expression is provided for a system consisting of two ultrathin films separated by a non-magnetic spacer and deposited on a non-magnetic substrate. The capabilities of the analytical expressions are demonstrated on MO spectroscopy in a broad spectral range of some well characterized ultrathin magnetic structures.

Spectroscopic PMOKE evidence of Au/Co segregation in a Au50Co50 cover layer deposited on Co(0001)/Au(111) with perpendicular anisotropy

Abstract We report the results of spectroscopic magneto-optic polar Kerr rotation experiments on Au/Au 50 Co 50 /Co/Au (111) ultrathin magnetic structures prepared by evaporation in UHV, with different Co and Au 50 Co 50 thicknesses and perpendicular easy magnetization axes. Previous in situ RHEED experiments have shown a surfactant effect during Au deposition on Co(0001) in the monolayer range. The spectroscopic MOKE data give new proof that during deposition of the alloy Au 50 Co 50 , separation takes place between the Au and Co; the Au atoms segregate and grow at the top of the Co layer.