Effect of thermophysical factors and magnetic field on the composition and optical properties of the surface of ribbons of amorphous cobalt- and iron-based alloys

Ellipsometric measurements of the surface of ribbons of amorphous Co₅₉Fe₅Ni₁₀Si₁₁B₁₅ and Fe₆₁Co₂₀Si₅B₁₄ alloys before and after thermal and laser treatments and Auger analysis of their surface layers have been performed in order to determine the character of changes in the composition of these layers after the noted treatments. It is found that magnetostriction significantly affects the processes of modification of the atomic structure of the surface layer of ribbons of amorphous iron-or cobalt-based alloys and formation of a microrelief of their surface from the noncontacting side after cryogenic treatments under the same conditions. Specifically, magnetostriction is characteristic of amorphous iron-based alloys and is responsible for the optical anisotropy induced in the skin layer. It is established that annealing of ribbons of a Co-based amorphous alloy, even at the temperature T = 425°C, changes the character of the spectral dependence of the IR optical conductivity of this alloy to that described by the Drude relation. This change fixes the beginning of ordering of the atomic structure of the surface layer of the material with the formation of microscopic crystallization regions.     

Optical properties and the magnetoimpedance effect in amorphous Co-Ni-B metal alloys

A magnetoimpedance effect is observed in Co_80–xNi_xB20 (x = 4, 6, 8, 10, 12) amorphous metal alloy ribbons when an alternating current at frequencies ranging from 1–3000 kHz is passed through samples in an external magnetic field. Spectra of the permittivity and optical conductivity of the surface of ribbons of these alloys are obtained for incident photon energies of 1.0–5.0 eV. The relationships between the magnitude of the magnetoimpedance effect, and the magnetic properties, electronic structure parameters, and optical characteristics of the amorphous alloy samples are determined.     

Electronic and topological parameters of the skin layer in amorphous metallic ribbons after thermal annealing

Data on spectral polarimetric measurements in the range of 0.05–0.60 eV are presented, along with calculations on the optical characteristics of the surface layers of ribbons of the amorphous alloy Co₅₉Fe₅Ni₁₀Si₁₁B₁₅ before and after thermal annealing in order to determine how the composition of the surface layer changes during this treatment. It is shown that after annealing at a temperature of 425°C or above, the optical conductivity and the real and imaginary parts of the dielectric constant revert to the values for typical metals in the IR. This treatment produces microregions with an ordered structure in the surface layer. The experimental data show that for ribbons annealed at T = 475°C the spectral optical characteristics do not obey the Drude relations and behave similarly to their amorphous analogs.     

Structure of natural film on porous silicon surface founded by ellipsometry

Abstract

The multiple-angle-of-incidence ellipsometric studies of the natural film formed on the surface of porous silicon sample after its production and subsequent keeping in isopropyl alcohol have been performed. A new property of porous silicon with the natural film on its surface has been revealed which consists in a drastic change of the polarization characteristics of the reflected light wave after its keeping in alcohol. This property of porous silicon may be the basis for the development of liquid and gas sensors, polarization elements of optical devices etc. It was found that ellipsometric curves are described better by calculations in a two-layer model in comparison with a single-layer one of the investigated film. It was obtained that the outer layer of the film has smaller refractive index than the inner one. As a result of decoration the refractive indices of both layers decrease and further the changes of refractive indices and the redistribution of the thickness of both layers are found. It is suggested that the interaction of the alcohol molecules with silicon and its oxide environment occurs in the walls of the pores during the decoration.     

Specific features of infrared absorption in films materials subjected to a magnetic field

The reflection spectra and magnetorefractive effect (MRE) of metal (Co, CoFe), semiconductor (Si, GaAs), and granular and amorphous Co₃₀Ag₇₀ and Co₅₉Fe₅Ni₁₀Si₁₁B₁₅ films are studied in the IR spectral region at λ=2.5–25 μm. It is found that the IR optical properties of the ferromagnetic metal films can be described with regard to light absorption due to electron transitions in the two spin systems. The MRE is found to occur in both the ferromagnetic (Co, CoFe) and semiconductor (Si, GaAs) films. The amplitude and shape of the MRE are determined for the p and s polarizations of light. It is shown that, to a first approximation, the IR optical properties of the films with giant magnetoresistance can be described by the Drude theory, while the MRE is explained on the basis of a modified Hagen-Rubens relation. Variations in the IR reflection of semiconductor or amorphous metal films in the magnetic field are found to depend on the degree of polarization of localized electron states at the Fermi level.     

Modification of the structure of bandpass reflection interference filters

Spectral properties of bandpass reflection interference filters, whose components represent interference transmission cutoff short-and long-wavelength filters, are studied. It is shown that the use of transmission cutoff filters provides a uniform suppression of background outside the transmission band of a bandpass reflection filter. A reflection filter becomes a virtually ideal polarizer for radiation incident on the surfaces inside a filter at angles of 35° and greater.     

Effect of Laser and Thermal Annealing on Optical and Structural Properties of Amorphous Metal Alloys

The results of ellipsometric measurements of rough and annealed amorphous alloys of 3d-transition metals (Fe, Ni, and Co) with metalloids are presented. Composition of alloys, directions of steady-state bonds between their compounds, and frequencies of the Auger electron transitions are determined by the methods of Auger spectroscopy and from the Raman spectra. Frequencies of metal-metalloid oscillations are determined and strains arising in nanoregions of the crystalline phase are obtained. Different characters of thermal and laser actions on the optical properties of alloys are established, and changes in the optical properties caused by these actions are compared.     

Interrelation between optical and magneto-optical properties of MnSbBi(Pt,Co) films

Results of the study of optical and magneto-optical properties of MnSbBi(Pt, Co) films in a spectral region of 360–820 nm are reported. It is shown that the multilayer MnSbBi(Pt, Co) films obtained by magnetron sputtering possess considerable optical rotation in the geometry of the polar Kerr effect, which is as large as 0.5°–0.7° upon 5-h annealing of the films at 350°C. The spectral dependences measured for the magnitude of the polar Kerr effect showed that these films may be used for laser data recording in the short-wavelength spectral region, which substantially increases the recording density. Studies of the film structure by X-ray and electron diffraction analysis showed that the films have a polycrystalline structure, with granules 15–40 nm in size. Possible causes of a large magnitude of Kerr effect are analyzed.     

Influence of the short-range order parameter on the optical properties of amorphous nickel-phosphorus alloy

The influence of the short-range order of amorphous nickel-phosphorus alloy on the IR absorption is studied. The relation between the optical properties and the microstructure of amorphous nickel-phosphorus alloys obtained by various technological methods is considered. It is shown that a coating of amorphous Ni−P alloy obtained by electrolytic deposition has the most homogeneous structure; this permits the use of such coatings as protective layers for optical and magnetic memory disks. Optical methods permitting the estimation of the dimensions of the microcrystalline regions in an amorphous matrix are outlined. T. Shevchenko Kiev University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 34–40. May, 1997.