D.J. Mapps

Generation of infrared surface plasmon resonances with high refractive index sensitivity utilizing tilted fiber Bragg gratings

We demonstrate the use of tilted fiber gratings to assist the generation of localized infrared surface plasmons with short propagation lengths and a sensitivity of dlambda/dn = 3,365 nm in the aqueous index regime. It was also found that the resonances could be spectrally tuned over 1,000 nm at the same spatial region with high coupling efficiency (in excess of 25 dB) by altering the polarization of the light illuminating the device.

Two-dimensional analysis of magnetoimpedance in magnetic/metallic multilayers

This article concerns the effect of the in-plane film size on the magnetoimpedance (MI) characteristics in magnetic/metallic multilayers. The problem is approached by a two-dimensional solution of the Maxwell equations in a symmetrical three-layer film. If the edge effect is neglected, the magnetic flux generated by the current flowing through the film is confined within the outer magnetic layers. In a finite width sandwich, the flux leaks through the inner conductor. This process eventually results in a considerable drop in MI ratio if this width is smaller than the critical flux decay length depending on the effective transverse permeability, layer thickness, and frequency.

Characterization of infrared surface plasmon resonances generated from a fiber-optical sensor utilizing tilted Bragg gratings

We demonstrate the use of tilted fiber gratings to assist with the generation of infrared surface plasmons on a metal film coating the flat of a D-shaped fiber. The wavelength of the strong (>25 dB) resonance is tunable over similar to 1000 nm by adjusting the polarization state of the light and is highly sensitive to the refractive index of any aqueous medium surrounding the fiber (sensitivity= 3365 nm).

Effect of induced anisotropy on magnetoimpedance characteristics in NiFe∕Au∕NiFe sandwich thin films

The high frequency magnetoimpedance (MI) has been measured in NiFe∕Au∕NiFe narrow sandwich thin films with transverse, longitudinal, and crossed magnetic anisotropies over a frequency range of 50–500MHz. The MI elements have an opened structure with lengths of 2 or 5 mm, widths of 50–200μm and a total film thickness of 1.5μm. The magnetoimpedance characteristics with different field curve shapes, including asymmetrical, have been realized for certain magnetic anisotropy using a dc bias current. Initially the different MI field characteristics have been demonstrated in ferromagnetic microwires with circumferential, helical, and longitudinal anisotropies. Here we have reintroduced these field characteristics for the MI sandwich thin film elements. In an attempt to induce a particular anisotropy in the films the magnetic layers were rf sputtered in the presence of a strong magnetic field, with a further thermal restress treatment of the final MI elements. The use of thin film technology for MI is preferable ...

Studies on the effect of Cobalt and Titanium substitution in NdFeB thin films for magnetic recording media

We have investigated as series of substituted NdFeB thin films (NdFeBX where X = Co, Cu, Ti, Zr partially replacing Fe) of different thickness. The perpendicular coercivity has a maximum of 2700 Oe for a thickness of 200 nm after annealing at 625°C for 15 mins. It is found that coercivity can be controlled by varying the thickness of the films. We have observed that the grain size is controlled to less than 25 nm in the substituted films.

Off-diagonal magnetoimpedance in NiFe-Au-NiFe layered film and its application to linear magnetic sensors

We have measured the field dependence of the off-diagonal impedance in the megahertz frequency range for a NiFe-Au-NiFe layered film using a helical microcoil. The film and the coil were deposited by means of radio-frequency sputtering, and a transverse anisotropy in magnetic layers was established by applying a dc magnetic field during the deposition and by postproduction annealing. The film had 5 mm length, 50 /spl mu/m width, and 1.5 /spl mu/m total thickness. The helical microcoil had 23 turns with a 50 /spl mu/m turn width. We applied high-frequency excitation by means of the coil current and measured the induced voltage across the film stripe. This voltage response is directly proportional to the off-diagonal component of the total impedance tensor. We found that the plots of the real and imaginary parts of the off-diagonal impedance, as functions of the applied dc magnetic field, are antisymmetrical with respect to the field direction. The dc bias current through the film plays an important role: without the bias current, the measured signal is very small and irregular. The field antisymmetry demonstrated by the off-diagonal impedance can be utilized in highly sensitive and linear magnetic sensors, and we discuss the principles of operation of such sensors here.

Two-dimensional coding for a multi-track recording system to combat inter-track interference

Increasing track density, through a narrowing of the read head, leads to a reduced signal-to-noise ratio and increased inter-track-interference (ITI). Two-dimensional codes for multi-track recording systems have demonstrated increased capacity over conventional single track run length limited (RLL) codes. This paper describes a two-dimensional code for a multitrack recording system to control ITI by preventing adjacent track transitions. Results show that such a code, when applied to a PRML channel, can significantly improve immunity to crosstalk whilst maintaining a high linear density.

CoNbFe soft magnetic thin‐film backlayers for glass computer disks

Co84Nb12Fe4 films with very low coercivity down to 1 A/m, anisotropy field 1100 A/m, and saturation magnetic induction 1.1 T have been deposited by rf sputtering onto chemically strengthened glass disk substrates as a backlayer for perpendicular recording Winchester disks. Values of coercivity and anisotropy field were studied over a thickness range from 30 to 15 000 A and found to be a strong function of film thickness. Comparisons between Neel’s prediction for wall motion coercivity mechanism and the experimental data were made. The experimental coercivity fits the Neel formula when films are thicker than 400 A. The dependence of coercivity and anisotropy field on deposition conditions was also characterized. The thermal stability of the films was studied by differential scanning calorimetry (DSC) and by thermal annealing up to 500 °C. The crystallization temperature of the CoNbFe films is about 450 °C determined from DSC analysis. Thermal annealing revealed that the magnetic properties were very stable...

Size and shape effects of patterned polycrystalline islands

Patterned polycrystalline cobalt islands with different sizes and shapes have been simulated by a micromagnetic simulator. An elliptic shape is found to be preferred for patterned islands to form a uniform single domain demagnetised state and have sharper squareness compared with square islands. Therefore, in a single-bit-per-island recording system, the elliptic islands could lead to a stable state and a predictable overwrite process and act independently even in a closely packed arrays.

Very thin CoCr films on titanium underlayers for high-density perpendicular recording computer discs

Very thin CoCr films with and without a Ti underlayer were deposited on strengthened glass disk substrates by bias RF-sputtering. Perpendicular M-H loops were successfully measured by a polar Kerr M-O loop plotter. Very pronounced effects of the Ti underlayer and bias on the shearing of the loop and the perpendicular remanence ratio were observed. X-ray diffraction results show excellent