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Lorentz electron microscopy, including a quantitative magnetisation-mapping technique, has been used to study the local magnetisation reversal mechanism in active spin-valve devices for correlation with the giant magnetoresistance and domain structure. Varying various parameters such as device size, applied current value and direction of easy-axis have been found to have an effect on the magnetisation reversal mechanism and on the GMR curve. Index terms - Lorentz microscopy, magnetisation reversal, spin-valve elements, giant magnetoresistance

In order to correlate giant magnetoresistance with changes in magnetic domain structure, we have studied lithographically-defined spin-valve elements in-situ by Lorentz transmission electron microscopy, whilst simultaneously passing a controlled current through the clement and applying a magnetic field. For a given current, the changes in magnetic domain structure can thus be correlated with changes in the resistance of the film. Spin valve structures with MnFe and MnNi pinning layers were examined and the technique proved particularly useful in identifying regions of the spin valve corrupted by corrosion of the pinning layer.

The design and recording performance of dual stripe magnetoresistive read/inductive write heads with read widths of 4 [[micro]meter] and write widths of 4.5 [[micro]meter] are described. A linear density of 75 kfci (D50) was measured in heads with shield-to-shield spacing of 420 nm and 70 nm of dielectric separating the two magnetoresistive stripes. Large signal amplitude, linear crosstrack profile, and good second harmonic suppression are observed in accordance with theoretical expectations. Readback waveforms contain little baseline shift and the ratio of positive to negative peak amplitudes is very close to unity. Stable signals are seen for heads with and without exchange stabilization. Conductor topography in the read head is replicated in the write head and can adversely affect cross-track behavior. Non-planarity of the write head must be considered in the design of shared pole magnetoresistive heads.

Bulk and local magnetoresistive responses in Ni-Fe thin films were measured as a function of applied magnetic field and field angle. The measurements were made using a four-probe resistance measurement system, which consisted of two scanning micro-probes for voltage taps, each less than 1 micrometer in tip diameter. The scanning resolution of the micro-probes was 0.5 micrometer. The system was used to determine domain formation and motion in magnetoresistive read heads. Longitudinal fields, produced by demagnetizing or external field components, may cause domain formation and subsequent domain-wall motion (and annihilation). This leads to Barkhausen noise, which is detrimental to the performance of the device as a magnetic read head. Experimental results for both the bulk and local responses were in qualitative agreement with micromagnetic theory.

High resolution electron microscopy (HREM) has been used to investigate the structure of Co(6nm)/Cu(2.8nm)/Co(4nm)/MnFe(12nm) spin valves so as to correlate the structure with the magnetic properties. The presence of a Ti seed layer enhances the structural quality of the film giving a strong texture and large grain size. It is shown that the texture favours a high exchange bias field. A numerical analysis of the HREM micrographs has been carried out in order to investigate more quantitatively the structure of the interfaces. It has been shown that locally they are diffuse over 2 monolayers in the growth direction.

A simplified geometric model is presented for analyzing the thermal conduction problem in magnetoresistive heads. The model leads to an approximate analytical solution for the thermal resistance as a function of the key geometric and material parameters. The model reveals trends that will be helpful in designing the next generation of high resolution recording heads.

A spin valve configuration is presented in which an unpinned ferromagnetic film is separated from exchange-pinned ferromagnetic films on either side by two nonmagnetic spacers, thereby creating a symmetric spin valve structure. The symmetric spin valve is shown to increase the magnetoresistance by 50% over the values of individual spin valves. The increase is attributed to a reduction of spin-independent outer boundary scattering and doubling the number of spin-dependent scattering interfaces. The magnetoresistance and coupling fields of the spin valves that comprise the symmetric structure have been measured as a function of Cu spacer thickness. Oscillatory antiferromagnetic to ferromagnetic coupling was observed in standard spin valves, which had AR/R as high as 13%.