Kerr Effect Spectra Research Articles

Surface effects and structural dependence of magneto-optical spectra: Ultrathin Co films andCoPtnalloys and multilayers

First-principles calculations of the optical conductivities and magneto-optical Kerr effects for bulk and thin films of Co and for ${\mathrm{CoPt}}_{n}$ alloys $(n=1$ and 3) and multilayer $(n=3)$ are carried out using the full potential linearized augmented plane wave method with the local spin density approximation. For fcc bulk Co, we obtain a negligible dependence of the polar Kerr rotation on the direction of magnetization. By contrast, the calculated Kerr spectra of ${\mathrm{CoPt}}_{n}$ are found to be very sensitive to structural changes. For Co(001) and Co(111) ultrathin films, the surface effects cause a redshift for the high-energy peaks in the magneto-optic Kerr effect (MOKE) spectra, mainly due to band narrowing. Except for the free standing Co(001) monolayer, the profile of their MOKE spectra, however, is very close to that of bulk Co.

Magneto-optical Kerr spectroscopy of palladium

Magneto-optical Kerr effect (MOKE) spectra of a paramagnetic fcc Pd metal film, measured with high sensitivity in an applied magnetic field of 1.5 T over a photon energy range 0.8--4.8 eV, are presented. Ab initio linear-muffin-tin-orbital calculations reproduce the experimental spectra well, and explain the microscopic origin of the magneto-optical (MO) response in terms of the individual interband transitions. A band-by-band decomposition of the fcc Pd MO spectra is presented, and transitions responsible for prominent structures in the spectra are identified. The dominant role of transitions from states in the vicinity of the Fermi level is found. It is found and explained that the proportionality between the magnitude of the MOKE spectra and the magnetic moment induced on the Pd atom holds over two orders of magnitude up to the value of $\ensuremath{\sim}0.25{\ensuremath{\mu}}_{B}$ typical for magnetic Pd compounds. It is shown that, in spite of the different mechanisms of the Pd magnetization, the MOKE spectra of the paramagnetic Pd metal in the external magnetic field are similar to the spectra of the ferromagnetic diluted Co-Pd and Fe-Pd alloys.

Large Filling-Factor-Dependent Spin Splitting in Magnetooptic Kerr Effect in GaAs/AlGaAs Multiple Quantum Wells

Magnetooptic Kerr effect in GaAs/Al0.312 Ga0.688 As multiple quantum wells was investigated in the integer quantum Hall regime. The measurements have been performed in magnetic fields up to 14.5 T, at the temperature of 1.8 K. Experimental data indicate the discontinuous behavior of the magnetooptic Kerr effect spectrum as a function of the filling factor. For odd filling factor values v = 3 and 5 we observe the large spin splitting. The effects cannot be explained in the one-particle model.

Structural stability, magnetism, and surface magneto-optic Kerr effect spectra of MnAg(001) surface alloys

The stability of a MnAg surface alloy was investigated employing the total energy and atomic force full-potential linearized augmented plane wave method based on the local density approximation for: (i) a clean Ag(001), (ii) 1 ML Mn overlayer [1 Mn/Ag(001)], (iii) 1 and 2 ML MnAg alloys as overlayers on Ag(001) [1(MnAg)/Ag(001) and 2(MnAg)/Ag(001)], and (iv) 1 ML Mn diffused into Ag(001) substrate [Ag/1 Mn/Ag(001)]. Results obtained show that 2(MnAg)/Ag(001) is much more stable than 1 Mn/Ag(001) (by a large energy difference of 150 meV), whereas 1(MnAg)/Ag(001) is marginally more stable (by a slight energy difference of 8 meV) compared to a separate phase of Ag and Mn atoms. Surface Mn and subsurface Mn atoms in 2(MnAg)/Ag(001) were found to be coupled antiferromagnetically with magnetic moments of 3.96 and −3.55 μB, respectively. The surface corrugation (Δz=0.05 a.u.) of 2(MnAg)/Ag(001) was found to be much smaller than that (Δz=0.5 a.u.) of another magnetically stabilized surface alloy system, MnCu/Cu(001). No significant magneto-optical effects for antiferromagnetic Ag/Mn/Ag(001) were found due to the small off-diagonal elements of the optical conductivity.

The influence of interface structure on the magneto-optical properties of Co/Pd multilayers

Magneto-optical Kerr effect (MOKE) spectra of Co/Pd multilayered structures (MLS), measured in the polar geometry over the spectral range 0.8-5.5 eV, are presented and compared to spectra obtained from ab initio band-structure calculations. It is shown that the MOKE spectra of the Co/Pd MLS calculated using the spin-polarized relativistic linear-muffin-tin-orbital method reproduce the experimental spectra only moderately well if ideal multilayer structures with sharp interfaces are assumed. Calculations of the magneto-optical (MO) response of MLS with imperfect interfaces modelled by introducing ordered compounds at the interface have also been performed. The results obtained reveal that the MOKE spectra of the Co/Pd MLS can be adequately reproduced using a model of limited interdiffusion within one or two atomic planes at the interface which results in the formation of a Pd-rich alloy. The role of the Pd spin polarization in the formation of the MO spectra as inferred from first-principles calculations is examined and discussed. Finally, the influence of thermal annealing on the MO properties of Co/Pd MLS is studied both experimentally and theoretically. The good agreement between the calculated spectra of the MLS and experimentally observed ones demonstrates the validity of the proposed models. The results obtained demonstrate the crucial role played by the interface microstructure in the formation of the MOKE spectra of the multilayered systems studied.

Structural transition of Fe and Co sublayers in Fe/Zr and Co/Zr multilayered films investigated by magneto-optical spectroscopy

The experimental and computer-simulation study of the magneto-optical properties (equatorial Kerr effect) of Fe/Zr and Co/Zr multilayered films was carried out. Drastic changes in the magneto-optical properties of the Fe/Zr and Co/Zr multilayered films were observed with the ferromagnetic sublayers that had less than the critical thickness. Such a behavior is connected with a polycrystalline–amorphous transformation in these sublayers. An annealing of the multilayered film led to a significant increase in the equatorial Kerr effect value which is caused by a partial crystallization of the amorphous Fe or Co sublayers. The real interface structures of the Fe/Zr and Co/Zr multilayered films were estimated by a fitting procedure between the experimental and the computer-simulated equatorial Kerr effect spectra of the multilayered films.

Magneto-optical spectra of long range chemically ordered FePd(001) alloy films

Magneto-optical and magnetic properties of sputtered epitaxial FePd (001) alloy films have been studied as a function of the film deposition temperature. Characteristic changes in the magnetic anisotropies and Kerr effect spectra are observed and correlated with the degree of long range chemical ordering.

Magnetooptical Kerr Spectra in Sputtered Strontium Ferrite Films

Magnetooptic (MO) polar Kerr effect spectra and MO hysteresis loops ofSrF 12 O 19 hexagonal ferrite films are presented. The films were prepared by rf sputtering and subsequently annealed at 800 or 900°C in O 2 /Ar. The crystallographic orientation with the c-axis perpendicular to the film plane was checked using XRD. The films display perpendicular magnetic anisotropy and rectangular hysteresis loops with a remanence ratio close to one. At low photon energies below the absorption edge of SrFe 12 O 19 at 2.5 eV MO spectra are affected by the radiation penetration into the film and the quartz substrate. Above this energy they display the features typical for bulk SrFe 12 O 19 crystals. The coercive field, structure of the MO spectra and the magnitude of the prominent peak in the spectra near 4.5 eV can be correlated with the structural quality of the films. Consequently, the magnetooptics can serve as a diagnostics tool for these films.

Dispersion of Ultrafast Optical Kerr Effect in No-aggregation Phthalocyanine Molecules

We report dispersion property for femtosecond optical Kerr effect in the solutions of no-aggregation 16 (trifluoro ethoxyl) vanadyl phthalocyanine in the wavelength range of 850-770 nm. The optical Kerr effect spectrum shows a broad near-resonant enhancement on the third-order non-linear optical response of the molecule.

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

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.

OPTICAL BEHAVIOUR OF Fe IN MAGNETIC MULTILAYERS

Magneto-optical (MO) polar and longitudinal Kerr effect spectra between 1.5 and 5.7 eV measured on series of magnetic multilayers Fe/Ag, Fe/AlN, Fe/Bi, Fe/V, Fe/Ta, Fe/Pt and TbFe/Pt with a varied thickness of ultrathin Fe are reported. The observed trends in the MO spectra can be explained using a 4×4 matrix model assuming the composition profile which incorporates interface transition layers. The aim of the paper is to demonstrate the effect of non-ferromagnetic spacer on MO spectra and to provide MO data for Fe suitable for the modeling of the optical interactions in Fe containing multilayers.

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

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.

Polar magneto-optics in simple ultrathin-magnetic-film structures.

For a better understanding of optical interactions in magnetic layered structures we establish general expressions of both polar Kerr and Faraday first-order magneto-optical (MO) effects. The approach presented here enables the MO response of an arbitrary magnetic layer system to be analytically expressed with an accuracy practically equal (less than ${10}^{\mathrm{\ensuremath{-}}4}$ deg) to that of the full matrix calculations usually employed for modeling MO effects in magnetic multilayers. The formulas for any particular structure are obtained from general MO expressions by introducing associated reflection and transmission coefficients. This procedure is justified here in the simple case of an ultrathin magnetic film sandwiched between two nonmagnetic layers. These accurate expressions are further simplified for ultrathin magnetic films and the limitations of this approximation discussed. The simplified formulas are then used to analyze MO polar Kerr and Faraday data in well-defined Au (5 nm)/Co/Au (25 nm) structures, grown on float glass substrates. The Co layer thicknesses are chosen in the range 0.4--2.0 nm to preserve a perpendicular magnetic anisotropy. The simplified expressions, as well as the numerical modeling of the trends in MO spectra with a variation of the overlayer or buffer layer thicknesses, show that the shape of the polar Kerr effect spectrum is mainly dependent upon the optical properties of the Au buffer layer whereas the observed MO amplitudes are reduced consistently with the absorption of the Au overlayer.

Low temperature magneto-optical studies of multilayers

Abstract Magneto-optical (MO) polar Kerr effect spectra in Ni Pt multilayers at 80 K show a strong increase in the spectra amplitudes, which exceeds that predicted by the model based on electromagnetic theory. An enhancement of the Kerr effect is observed at photon energies above 3 eV, similar to that in Co Pt and Fe Pt .

Enhanced magneto-optical Kerr effect in spontaneously ordered FePt alloys: Quantitative agreement between theory and experiment.

A chemical-ordering-induced peak in the polar magneto-optical Kerr effect spectra of FePt compounds is found to be in quantitative agreement with predictions based on ab initio magneto-optical calculations. Experimental spectra of epitaxial molecular-beam-epitaxy grown FePt(001) films reveal a more than twofold enhancement of the Kerr rotation if full chemical ordering is present. A spectral feature at 2-eV photon energy shows a peak Kerr rotation of up to \ensuremath{\sim}0.8\ifmmode^\circ\else\textdegree\fi{}, which is strongly correlated with the presence of perpendicular magnetic anisotropy in ordered compound films.

Magneto-optical Kerr spectra of nickel

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 complex polar Kerr effect spectra in iron-silver multilayers

Complex polar Kerr effect spectra in rf-sputtered Fe/Ag multilayers were measured in the spectral range 1.5–53 eV in a magnetic field of 0.45 T. The thicknesses of the individual iron layers in the three samples investigated were 11, 3.6 and 0.6 mm, while that of silver was kept at 6 nm. The observed spectra are explained in terms of the electromagnetic interaction in planar magnetic multilayer systems using published optical constants of iron and silver.

Magneto-optical Kerr Effect of NdFe Films and NdFe/Cu(Al) Bilayers

In this paper single layer NdFe film, bilayer NdFe/Cu and NdFe/Al films made by vacuum evaporation were studied. The magneto-optical Kerr effect (MOKE) and reflectivity spectra were measured. The following results were found: the contribution of Nd to MOKE is mainly at short wavelengths, for NdFe/Al the MOKE enhancement locates in the short wavelength range and for NdFe/Cu the enhancement peak locates near the absorption edge of reflector Cu, and in the MOKE spectra of bilayer NdFe/Cu film with some compositions, sign reversals were observed.

The magneto-optical Kerr effect of bilayer films Nd-Fe/Cu and Nd-Fe/Al

Bilayers Nd-Fe/Cu and Nd-Fe/Al made by vacuum evaporation were studied. The magneto-optical Kerr effect (MOKE) and reflectivity spectra were measured. For Nd-Fe/Cu with low Nd content and small thickness of Nd-Fe layer there is a peak in the MOKE spectrum and a broad MOKE enhancement. The position is located near the plasma edge of Cu. When the content of Nd exceeds 37 at. %, there is no Kerr peak in the MOKE spectrum of Nd-Fe/Cu. When the thickness of the magnetic layer is larger but still less than the light penetration depth, the position of the peak moves towards the long-wavelength side. For Nd-Fe/Al there is a broad enhancement in the short-wavelength region, but no Kerr peak occurs no matter how the magnetic layer changes. The results presented show that the necessary conditions for MOKE enhancement in bilayers are suitable values of n and k of the reflector, whether the reflector has a plasma edge or not, and the enhancement also depends on the properties of the magnetic layer.

Nonlinear magneto-optical Kerr effect on a nickel surface.

Nonlinear surface optics is being developed as a useful new tool in surface science. In this work, we calculate the second-order magneto-optical response function in order to determine the nonlinear magneto-optical Kerr effect. This is applied to the surface of ferromagnetic nickel. We take into account the realistic spin-polarized nickel band structure and the spin-orbit coupling, but treat the transition-matrix elements as constants in a first approximation. We calculate nonlinear Kerr spectra which should be observable in surface second-harmonic-generation experiments. As a check of our calculations we determine the linear magneto-optical Kerr effect (MOKE) spectra for bulk nickel and find good agreement with experiment.