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The behavior of magnetoresistance in NiFe (permalloy) point junctions was investigated using an STM set-up, where the junction resistance was continuously varied from [10.sup.8] [OMEGA]-[10.sup.3] [OMEGA]. Our results reveal an enhancement of magnetoresistance of more than 80% at one conductance quantum, and the decaying magnetoresistance as one moves away from 12.9 k[OMEGA] to either the diffusive regime or the tunneling regime, as supported by independent theories on spin-dependent transport. The suppression of magnetoresistance with incorporation of a 35-nm-thick Au barrier was observed, as well as the dependence of magnetoreslstance on the relative orientations of the electrodes. Index Terms--Ballistic magnetoresistanee, magnetoresistance, scanning tunneling microscope (STM).

The topographic and electronic structure of 10-20-nm-thick permalloy films has been investigated under ultrahigh vacuum conditions. The films were characterized using scanning tunneling microscopy/spectroscopy. Permalloy grows as a polycrystalline film. The size of the crystallites is in the range of 5-20 nm for the permalloy films. The spectroscopic data show a distinct minority electron state, which can be assigned to the presence of iron in the permalloy surface. It was found that the state not only decays but also shifts in position when moving the STM tip away from the center position of the iron atoms. Index Terms--Chemical identification, permalloy, scanning tunneling microscopy, scanning tunneling spectroscopy.

In this work, we study the elastoresistance of CoFe/Cu antiferromagnetically coupled giant magnetoresistive films. This refers to variations in resistivity due to strain-induced changes in magnetization. This type of phenomenon, observed on a multilayer, originates mainly from the inverse magnetostriction effect, taking place within the magnetic layers. Since these magnetizations are coupled, strain induces an overall effect on the film resistivity. Our measurements reveal that these effects lead to enhanced strain sensitivity in comparison to films made of the materials the materials that compose the multilayer. Index Terms--Giant magnetoresistance, magnetoelasticity, strain measurement.

Both ferromagnetic (FM) and charge-ordered domain structures of [([La.sub.1-x][Pr.sub.x]).sub.0.67][Ca.sub.0.33]Mn[O.sub.3] thin film were detected by magnetic force microscopy (MFM) and electric force microscopy (EFM) operated at low temperatures near the peak resistance temperature ([T.sub.p]). The in-plane-like FM domains of submicrometer size emerge below [T.sub.p], and their magnetic interaction with an MFM tip becomes stronger as the temperature is reduced. Charge-ordered insulating regions have the strong electrostatic interaction with an EFM tip near [T.sub.p], and the interaction correlates well with the temperature dependence of resistivity of the film. Index Terms--Charge ordering, colossal magnetoresistance, EFM, low temperature, magnetic domain, MFM.

The switching characteristics of submicron permalloy elements were systematically studied as a function of interisland spacing. The result was an increase of the switching field with reduction in spacing, with a maximum value for near zero spacing. However, in overlapped segments, all elements switched simultaneously at lower fields than the maximum at zero spacing, The switching field depends on the number of connected segments as described by the Jacobs-Bean model, whereas the switching of the separated islands is governed mainly by the field emanating from the nearest-neighbor magnetic poles. The reversal behavior of the branched contiguous array was also studied. The angle between the branch axis and the easy axis played a critical role in establishing the switching field. The reversal field of the branched segment reached a minimum at 45[degrees] and a maximum at 90[degrees]. A coherent rotation model, which includes the effect of the array geometry, appears to explain the trends. Index Terms--Angle, array, coherent rotation, interisland spacing, permalloy, switching field.

The topographic and magnetic structures of patterned 20-nm-thick Fe films grown on Si (001), polycrystalline NiO, and Si[O.sub.2] substrates are compared by scanning tunneling microscopy/magnetic force microscopy measurements under ultrahigh vacuum conditions to investigate the influence of the different substrates. Iron grows as a polycrystalline film. The size of the crystailites decreases from Si to NiO and Si[O.sub.2] substrates, respectively, while the surface roughness increases. The increased disorder in the film structure does not necessarily lead to an increased disorder in the magnetic domain structure. Instead, the magnetic structure of iron on NiO is the most complex, which can be attributed to the exchange coupling to the substrate. The antiferromagnetic NiO crystallites exhibit no long range crystallographic ordering which leads to random magnetic orientation. More evidence of the influence of the exchange coupling is found when comparing the magnetic structures of iron on NiO and Si[O.sub.2] as a function of film thickness in the range of 0-10 nm. Index Terms--Magnetic force microscopy, patterned films, scanning tunneling microscopy, ultrahigh vacuum, ultrathin iron films.

The Magnetic Force Microscopy (MFM) image reconstruction technique has overcome difficulties in interpreting MFM images of data tracks written on longitudinal recording media. In this work, MFM image reconstruction is used to study the vector magnetization components of closely spaced tracks. Untrimmed and Focused-Ion Beam (FIB) milled, trimmed thin-film inductive heads of widths 4.5[[micro]meter] and 2.5[[micro]meter] are used to write tracks with wavelengths ranging from 0.75[[micro]meter] to 3[[micro]meter]. In order to analyze the limitations of high density recording, the magnetization at the edges of neighboring tracks is considered. It is shown that the width of the cross-track component of magnetization is strongly dependent on the relative phase difference of adjacent tracks, the track width, and the linear recording density.

The role of stress on magnetic properties of epitaxial ([La.sub.0.7][Sr.sub.0.3])Mn[O.sub.3] (LSMO) films has been studied. We have investigated 1100 [Angstrom] thick LSMO films deposited on LaAl[O.sub.3] (Sample L, under a compressive stress) and SrTi[O.sub.3] (Sample S, under a tensile stress) using the magnetic force microscopy (MFM), DC hysteresis loop, ferromagnetic resonance (FMR) measurements. The magnetic force microscope image of Sample L shows a 'maze-like' pattern indicating a sizable out-of-plane magnetization, while the magnetic image of Sample S shows a 'feather-like' pattern indicative of an in-plane magnetization. The hysteresis loop and ferromagnetic resonance measurements give quantitative evidence for the role of the lattice mismatch between the film and the substrate in the magnetic anisotropy of the two films. Our systematic examination of various thickness LSMO films on LaAl[O.sub.3] reveals that the maze pattern is exhibited only between 500 [Angstrom] and 1700 [Angstrom] thick films. Despite of larger anisotropy, no maze pattern is observed in films thinner than 360 [Angstrom].

Patterns of submicron cobalt islands were created on silicon by using self-assembled co-polymers as etching masks. The synthesis conditions were varied to create specific magnetic island morphologies. The magnetic structure and magnetization reversal of interconnected, as well as interacting and non-interacting islands were systematically studied using magnetic force microscopy. Differences in magnetic characteristics were observed and correlated with the thin film morphologies. The result of these studies include the transition from single to multidomain configuration as a function of island size, domain boundary characteristics near coercivity, evidence of magnetization rotation with increasing reverse magnetic field, and evidence of collective switching behavior in interacting single domain islands.

A novel experimental technique of magnetic biasing for the Magnetic Force Microscopy (MFM) imaging is introduced. This technique enforces linearity of the imaging system and, in this way, it facilitates the interpretation of images of magnetization patterns. The technique of numerical reconstruction of the curl-free vector magnetization from a raw image obtained by the linearized MFM system is presented. An example is given which demonstrates the significant difference between the reconstructed magnetization and the raw image. This stresses the usefulness of magnetic biasing and image reconstruction for MFM image interpretation.

A newly developed vector Preisach-type model of hysteresis is applied to the computation of static magnetic fields in media with hysteresis. Time stepping technique is used to trace the time evolution of local magnetic fields which form the history of magnetizing process. At each time step, the magnetostatic problem is formulated in terms of an integral equation and an efficient iterative algorithm is employed for solving this problem. The technique has been used to simulate some magnetic recording processes. Sample results of these simulations are given in the paper.

We have made a theoretical analysis of the interaction between a flexible triangular probe and a typical magnetic pattern on a recorded surface. The use of this analysis allows the measurement of the magnetic fields of the recorded patterns imaged by a tunneling magnetic force microscope.

The magnetic force scanning tunneling microscopy is briefly discussed and demonstrated to successfully image overwritten data on commercial rigid magnetic disks. In particular, clear images of unerased remnants of the previously stored data are presented. These unerased data are attributed to slight radial deviations in write head tracking due to the intrinsic limitations in the electromechanical positioning of the head.