M. Nyvlt

Magnetically textured γ-Fe2O3 nanoparticles in a silica gel matrix: Optical and magneto-optical properties

Optical and magneto-optical properties of maghemite superparamagnetic particles dispersed (f=0.28 vol % γ-Fe2O3) in a silica gel matrix have been studied at room temperature in the 1.5–3.7 eV spectral range. A permanent optical anisotropy can be induced when applying a magnetic field during the sol-gel freezing process. The permanent linear dichroism and birefringence in such in-plane magnetically textured samples are attentively studied. The spectral dispersion of Faraday effects in our textured samples is analyzed taking into account the in-plane optical anisotropy. Such a composite material is a promising candidate for future magneto-optical applications.

Magneto-optical effects in Au/Co/Au ultrathin film sandwiches

Abstract This paper deals with the study of magneto-optical effects exhibited in perfect Au/Co/Au ultrathin films structures as a function of magnetic field and photon energy. They stand as ideal basic structures to test theories describing the magneto-optical effects in multilayers. In both optical transmission and polar Kerr rotation dispersion spectra, the main feature is a prominent peak centered near the photon energy of 2.5 eV, which corresponds to the plasma edge and reflectivity minimum in gold. The observed trends in magneto-optical effects are explained using the electromagnetic wave theory starting from the published optical and magneto-optical constants values in gold and cobalt thick films. The polar Kerr effect in our samples is a sum of one independent plus one linearly dependent term on the Co film thickness. The nonzero value of the thickness-independent term indicates the presence of a contribution not accounted for by the employed electromagnetic wave model.

Magneto-optical studies of Pt/Co multilayers and Pt-Co alloy thin films

The authors consider magnetooptical spectroscopic studies of Pt/Co multilayers grown onto glass by dual electron beam evaporation an RF-sputtered Co rich Pt/sub x/Co/sub 1-x/ alloy films. Simultaneous polar and longitudinal magnetooptical Kerr experiments were carried out in the spectral range between 1.5 and 5.2 eV. The effect of the deposition temperature and that of subsequent heat treatment on the Kerr spectra is studied. In alloys Kerr rotation reached the value of 0.66 deg at 4.3 eV for x=0.41. >

Structural, magnetic, and spectroscopic magneto-optical properties aspects of Pt–Co multilayers with intentionally alloyed layers

Polycrystalline Pt–Co multilayers with intentionally alloyed layers were grown by e-beam evaporation on polyimide, Si, and glass substrates. X-ray diffraction spectra show that the multilayered structure of the samples degrades as compared to conventional Pt–Co multilayers. This degradation depends on the compositional variation of the intentionally alloyed layers. Magnetometry measurements reveal enhanced magnetization values for all samples, exceeding even by 90% the one of bulk Co, at a temperature of 10 K. This is attributed to both Pt-induced and enhanced Co magnetic moments, according to x-ray magnetic circular dichroism experiments. Spectroscopic magneto-optic measurements reveal large negative polar Kerr rotation maxima at photon energies between 4 and 4.4 eV due to the intense magneto-optic response of spin-polarized Pt.

Structural and spectroscopic magneto-optic studies of Pt–Ni multilayers

Ptm–Nin multilayers were grown by e-beam evaporation under ultrahigh vacuum; m and n will depict the number of atomic planes of the corresponding constituents in one modulation period and, in this work, they were varied between 1 and 14. X-ray diffraction and conventional electron microscopy experiments revealed a fcc polycrystalline structure with excellent modulation. Magneto-optic properties, studied at room temperature between 1.5 and 5.2 eV, were found to depend strongly on both m and n. Perpendicular anisotropy was exhibited for samples with thin Ni layers and, unexpectedly, for thicker Ni layers when Pt layers became considerably thin (m∼2). Comparison of the magneto-optic features of two similar samples grown on glass and polyimide revealed that the choice between glass and polyimide does not affect magneto-optic properties.

Magnetooptic depth sensitivity in a simple ultrathin film structure

Abstract Polar magnetooptics (MO) is able to probe the magnetization depth profile in ultrathin magnetic film structures on a nanometer scale. This information can be deduced by modelling the MO effects in the considered layered medium when performing MO experiments with a compensator or changing the wavelength of the incident light beam. Spectroscopic MO measurements are then helpful for analysing this phenomenon in detail. The in-depth selectivity of MO effects for magnetization is demonstrated for a simple ultrathin film structure consisting of two magnetic Co layers with perpendicular anisotropy separated by a non-magnetic Au spacer layer. The individual magnetic contributions of the two Co layers may be observed directly when performing MO Kerr measurements at selected compensator phase shifts or photon energies. The experimental data are interpreted by MO calculations in both cases.

Ellipsometric and polar Kerr spectroscopic studies of Pd-Ni and Co-Pt multilayers

Abstract Spectroscopic ellipsometry and the polar Kerr effect were studied for Pd-Ni and Co-Pt multilayers as well as the corresponding homogeneous alloys. Additional features in the dielectric function and the plasma frequency as well as the magneto-optic properties were observed to depend on the modulation and the layer thicknesses. The magneto-optic properties of Co-Pt were found to correspond more to the alloy than in Pd-Ni.

Magneto‐optical Kerr spectroscopy in Pt‐Ni multilayers

The magnetic multilayers consisting of ultrathin 3d‐transition metal and Pt or Pd layers are considered for the magneto‐optical storage media with increased information density. This paper reports on the magneto‐optical polar Kerr rotation and ellipticity spectra in Pt‐Ni multilayers at photon energies from 1.5 to 5.2 eV prepared by evaporation onto glass substrates. The thickness of individual Pt layers was kept constant at 2 nm in all samples studied while that of Ni layers varied between 0.9 and 3.9 nm. The prominent feature of the Kerr rotation spectra is a broad negative peak the amplitude of which increases with the individual Ni‐layer thickness. The multilayer spectra show less structure than that of pure Ni. Nevertheless the trends in multilayer spectra when the thickness of individual Ni layers changes can be reasonably simulated using the electromagnetic wave theory and permittivity spectra in bulk (or thick film) Ni and Pt.

Magneto-optic multilayers: Fundamental and technological aspects

Abstract We describe our magnetic and magneto-optic (MO) studies on some multilayers based on Ag, Au and Pt, such as Fe/Ag, Fe/Pt, CoNi/M (M = Pt, Au) prepared by evaporation under UHV conditions. In CoNi/M, the surface anisotropy increases linearly with the addition of Co verifying the single ion model. The Curie temperature can be tailored by the addition of Co without affecting adversely the properties of interest for MO storage applications. For instance, in Fe/Ag, the MO effect shows enhancement due to Ag plasma resonance and in Fe/Pt the effect is due to interaction of Pt. The spectra can be explained by a phenomenological model though quantitative agreement is not obtained. In Au-based multilayers, the MO Kerr spectra show the effect of plasma resonance of Au, particularly for thinner layers. Some of the results could be modelled by electromagnetic model. The Kerr spectra for CoNi alloy films could also be modelled with success using effective medium theory which also confirms the absence of any effect from hybridisation between Co and Ni a result which supports our conclusions on the surface anisotropy.

Magneto-optic spectroscopic Kerr effect in Co-based multilayers with layer-alloyed modulation

Abstract The magneto-optic (MO) polar-Kerr-rotation and ellipticity were studied at room temperature, between 1.5–5.2 eV, for CoPt, Co[CoPt], Co[CoPd] and Pt[CoPt] multilayers grown on Kapton, Si and glass in UHV. The MO properties were found to depend on the modulation-layer thicknesses. The results were reproduced theoretically in conjunction with the alloying modulations.