I.W. Salter

Optical and magneto-optical properties of Co-Ti-substituted barium hexaferrite single crystals and thin films produced by laser ablation deposition

Ellipsometry, reflectance photometry and Kerr polarimetry have been used to determine the optical and magneto-optical properties of bulk single-crystal platelets and thin films of Co-Ti-doped barium hexaferrite. The single crystals were grown by a slow-cooling flux method and the thin films were produced by pulsed laser ablation deposition onto single-crystal Al2O3 substrates at 840°C. The complex refractive index (n) and magneto-optic Voigt parameter (Q) were determined over the spectral range 350–850 nm and the reliability of the data tested by comparison with photometric measurements of reflectance. Although the optical constants of the thin films could not readily be obtained over the entire spectral range by ellipsometry, their magneto-optical performance in terms of the Kerr rotation and ellipticity compared well with predictions based on the fundamental data for the bulk material.

Quadrilayer magneto-optic enhancement with zero Kerr ellipticity

Abstract An analytical approach is used to develop a systematic method for designing magneto-optic quadrilayer structures which maximize the signal-to-noise ratio associated with readout systems utilizing differential detection of the Kerr effect. This new technique of optimizing the performance of magneto-optic recording media relies on the possibility of achieving two important requirements. First, the maximization of the Kerr component, and second, the reduction to zero of the phase difference between the Kerr component and the normal Fresnel reflection component. This means that quadrilayer structures can be produced which, for any pre-determined reflectance, will have a maximum Kerr rotation and zero ellipticity. It is also emphasized that the reflectance of the recording surface which maximizes the signal-to-noise ratio is determined only by the levels of electronic and shot noise in the detection system.

Substrate temperature and oxygen pressure dependence of pulsed laser-deposited Sr ferrite films

The effect of substrate temperature and oxygen pressure on the microstructure, magnetic and magneto-optical properties of Sr ferrite (SrM) films grown on (001) single-crystal sapphire substrates by pulsed laser deposition has been investigated. Polycrystalline SrM films with perpendicular magnetic anisotropy could be prepared under a wide range of oxygen pressures and relatively high temperatures, sufficient to crystallise the material. However, an almost exclusive c-axis orientation normal to the film plane could be attained only at a narrow operational window centered at 0.1 mbar and 840°C. The magneto-optical properties of the films were comparable to those of the bulk barium hexaferrite single-crystal material. In addition, results obtained by atomic force microscopy provide convincing evidence that the growth of Sr ferrite on sapphire takes place by a spiral growth mechanism.

Fundamental optical and magneto-optical constants of Co/Pt and CoNi/Pt multilayered films

A study has been made of the optical and magneto-optical properties of several Co/Pt and CoNi/Pt multilayered films that were fabricated by magnetron sputter deposition. Spectroscopic rotating analyzer ellipsometry and Kerr polarimetry were carried out to determine the fundamental optical and magneto-optical constants over the spectral range 320?860 nm. The constants determined were the complex refractive index and the first-order magneto-optic Voigt parameter. A total of seven films were examined and excellent reproducibility was observed in the measured material constants. These have been used to discuss the spectral dependence of the figure-of-merit, for each material, associated with the detection of the polar Kerr effect.

Optical and magneto-optical properties of TbFeCo films

Abstract The fundamental optical and magneto-optical constants of rare-earth—transition-metal (RE-TM) alloys in the form of TbFeCo thin films have been measured using spectroscopic ellipsometry. The films were produced using conventional dc-magnetron sputtering from composite targets and were deposited on thin glass substrates. A comprehensive set of ellipsometric measurements were performed on several thick (> 100 nm) films using radiation incident at both the air-film and film-substrate interfaces. For the purposes of confirming the reliability of the computed optical constants ellipsometric measurements were also carried out on films protected by a thin ( ∼ 15 nm) overlayer of silicon dioxide. Further verification of the usefulness of the computed constants was made by using them to predict the complex normal-incidence Kerr rotations and comparing these with actual values, measured using a normal-incidence Kerr-effect polarimeter.

Optical and magneto-optical properties of Co/Ti substituted barium ferrite

The optical and magneto-optical properties of single crystal Co/Ti doped barium hexaferrites have been measured over the wavelength range 400–800 nm. The spectral dependencies of the Kerr effect indicate that at short wavelengths Fe3+, and at long wavelengths Co2+ ions, are responsible for the M.O transitions. In the near IR, and after quadrilayer enhancement, heavily doped ferrite performs better than TbFeCo as an M.O recording medium.

Design, fabrication, and performance of enhanced magneto-optic quadrilayers with controllable ellipticity

An outline is given of a technique for designing quadrilayers that enhance the magneto-optic polar Kerr effect by maximizing the signal-to-noise ratio associated with readout systems utilizing differential detection. The method is particularly novel in that it produces maximized Kerr rotations with controllable ellipticities by using a systematic design procedure that does not involve computer-driven iterative techniques that search for optimum film structures. A number of quadrilayers, based on the ZnS-TbFeCo-ZnS-Al system, have been prepared using rf and dc sputtering and conventional evaporation techniques. The performance of the devices in terms of the basic optical and magneto-optical functions is good compared with theoretical predictions, both at the design wavelength and at all other regions of the spectrum, in the range 400-800 nm.

Optical and magneto-optical characterization of TbFeCo and GdFeCo thin films for high-density recording

Thin, optically semi-infinite films of amorphous TbFeCo and GdFeCo, suitable for magneto-optical recording, have been deposited by DC magnetron sputtering onto glass. Ellipsometric techniques have been used to determine the complex refractive index and complex magneto-optical parameter of the films in the wavelength range 400–900 nm, thus characterizing the materials. A review of the literature is presented and shows that the results for the TbFeCo films compare favourably with published results obtained from measurements conducted in situ, with the films protected with ZnS barrier layers. It is found that GdFeCo and TbFeCo are optically very similar, but magneto-optically the materials are quite different.

Magneto-optical properties of Sr-ferrite films produced by pulsed laser ablation

The effect of substrate temperature and oxygen pressure on the microstructure and magneto-optical (m-o) properties of Sr-ferrite films grown on [001] single crystal sapphire substrates by pulsed laser deposition has been investigated. The results demonstrated that smooth c-axis oriented films, could only be prepared at a narrow operational window of the useful oxygen pressure and at high substrate temperatures. The best films were deposited at a substrate temperature of 840/spl deg/C, and in an oxygen atmosphere of about 0.1 mbar. These were of good optical quality, hard to scratch, with c-axis oriented perpendicular to the film plane and exhibited bulk m-o properties.

Optical and magneto-optical properties of MBE grown Co/Au multilayers

Abstract The optical and magneto-optical properties of Co/Au multilayers, grown by molecular beam epitaxy (MBE), have been examined in the wavelength range 300 to 900 nm using ellipsometry and normal incidence Kerr polarimetry. The dispersion of fundamental optical and magneto-optical constants and the complex Kerr rotation are discussed in terms of the interaction of electromagnetic radiation with a multilayered structure. This is done on the basis of a single equivalent layer approach for dealing with multilayered media using values for the optical constants of cobalt and gold measured on single films of these materials grown by MBE. It is suggested that a restriction of the mean free path of the conduction electrons in the gold layers, of the order of the individual sub-layer thickness, accounts for some aspects of the observed optical spectra.