R.P. Ferrier

Side writing/reading in magnetic recording

Side writing is a significant effect for narrow track widths used in high‐ areal‐density magnetic recording. Lorentz electron micrographs can help to understand the nature of side writing and are used in this paper, in conjunction with analytical modeling, to characterize side writing in isotropic and strongly oriented recording media. Isotropic media exhibit a wide side‐written fringe, including a strip often termed an ‘‘erased band,’’ although it is not truly erased. Strongly oriented media, however, show no erased band.

Quantitative field measurements from magnetic force microscope tips and comparison with point and extended charge models

In this article we present results and analysis from measurements of the field distributions from standard magnetic force microscope tips. These measurements are made using Lorentz microscopy and tomographic reconstruction techniques with the field reconstructed in a plane situated about 50 nm from the end of the magnetic force microscope (MFM) tip; this corresponds approximately to the sample plane in the MFM. By examination of the experimental results and comparison with simulated field distributions from point and extended charge distributions, we conclude that the magnetization configuration of the tip is best represented by an extended charge distribution and that the point pole approximation represents only, at best, the central part of the field distribution.

Characterisation Of MFM Tip Fields By Electron Tomography

Lorentz electron microscopy has been applied to the study of the magnetic field distribution from MFM tips. Data acquired by this technique has been used to reconstruct the field distribution from the MFM tip by tomography. Initial results have been obtained from commercial tips which have been magnetised along the tip axis. The reconstructed field is consistent with the predicted form.

Magnetisation distributions in thin film recording heads by Type II contrast

The magnetic domain structure of the polepieces of thin-film magnetic recording heads and its variation with drive current and frequency are of interest in understanding the read/write properties of the head. The authors describe the setting up of the synchronous detection mode of type II backscattered electron contrast in a 200-kV electron microscope and its application to the study of domain wall movement in the P2 polepieces of heads with and without the 15-20- mu m-thick alumina overlayer in place. Extension of the method to allow evaluation of the changes in magnetization directions under AC drive conditions is described. The authors also demonstrate a novel technique which gives information on the remanent state of the domain structure in the P2 polepiece and its changes under DC drive conditions. It is concluded that these improvements in technique, taken together with the capability of the synchronous detection method to provide information on changes of magnetic structure with depth, mean that this experimental tool will be invaluable in its own right as well as complementary to the Kerr imaging methods. >

Electron beam tomography of magnetic recording head fields

The quantitative evaluation of the 3D form of the magnetic field from a thin film recording head has been achieved by electron beam tomography. The data sets for tomographic reconstruction were obtained using the differential phase contrast mode of Lorentz electron microscopy applied in a 200 kV (scanning) transmission instrument. The high accelerating voltage and a novel method of mounting the head in the microscope offer advantages over previous experiments. The two reconstruction algorithms, which have been used previously, have been implemented and the results of their application are compared for theoretical data derived from a model head field and for data obtained experimentally from a production recording head.

The determination of transition noise by Lorentz electron microscopy

The transition noise in a highly oriented magnetic film medium is analyzed with reference to the development of quantitative techniques to relate micromagnetic domain images obtained by Lorentz electron microscopy to the measured noise and signal for the medium. In general, the agreement between electronically derived and image-derived noise is excellent. It is demonstrated that micromagnetic imaging and analysis for this type of recording medium is sufficiently quantitative to justify using Lorentz micrographs to explore the origin and nature of transition noise. The proper interpretation of spectral analyses of finite field-of-view images is also clarified, i.e. it is shown that for noise analysis, only the minima of the spectra potentially contain valid noise information. The lobes contain mostly (scattered) signal information. >

Electrostatic charging artefacts in Lorentz electron tomography of MFM tip stray fields

Using the technique of differential phase contrast (DPC) Lorentz electron microscopy, the magnetic stray field distribution from magnetic force microscopy (MFM) tips can be calculated in a plane in front of the tip using tomographic reconstruction techniques. Electrostatic charging of the tip during DPC imaging can significantly distort these field reconstructions. Using a simple point charge model, this paper illustrates the effect of electrostatic charging of the sample on the accuracy of tomographic field reconstructions. A procedure for separating electrostatic and magnetic effects is described, and is demonstrated using experimental tomographic data obtained from a modified MFM tip.

Lorentz image-derived film media noise

Noise from thin-metal-film media is derived directly from Lorentz electron microscope images of the micromagnetic domain structure. In this first attempt to extract quantitative information from such images, Fe-Co-Cr alloy, a medium that is more easily interpretable than many others, is selected. For initial simplicity, noise from a bulk AC-erased disk is the focus of this analysis, rather than transition noise. A flux-noise spectrum is obtained from an image by processing and is compared with the same noise spectrum measured through a thin-film head flying over the disk. >

Preparation and characterisation of a new amorphous tip coating for application in magnetic force microscopy

Abstract Using sputter deposition, we have coated standard silicon pyramidal force microscopy tips with an amorphous ferromagnetic film. The film composition is close to that of the commercial METGLAS ® 2605SC amorphous ribbon. Using a NIST magnetic imaging reference sample, and a Digital Instruments Dimension 3000 microscope platform, we demonstrate the good spatial resolution of the coated tip, and that it behaves in a manner consistent with a magnetic moment intermediate between currently available commercial tips and those possessing a low coercivity. Using Lorentz electron tomography techniques, the stray field pattern of the tip in the remanent state was shown to be consistent with a magnetic moment aligned along the tip axis.

Characterisation of FeBSiC coated MFM tips using Lorentz electron tomography and MFM

Magnetic force microscope (MFM) tips coated with an amorphous ferromagnetic alloy have been studied using MFM and Lorentz electron microscopy. Imaging a standard NIST hard disk sample in the MFM reveals that the character of the tips varies dramatically with film thickness. The stray field distributions of the tips were determined using Lorentz electron tomography, and were found to be consistent with the contrast observed by MFM.