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In this paper, an experimental investigation of current-induced noise in current perpendicular-to-plane spin-valve heads is reported. It is found that the sense current yields excitations of coherent spin waves as well as substantial 1/f-like noise when current exceeds a critical value. The noise is magnetic in nature. The criticality and current directional dependence of the noise excitation clearly show that the spin transfer is the cause. Index Terms--Current perpendicular-to-plane (CPP) spin-valve read heads, spin transfer, 1/f noise.

In this paper, we present a quantitative micromagnetic modeling analysis of head stability in in-stack biased current perpendicular to plane (CPP) spin valve (SV) heads at deep submicron track widths. It is found that sufficient pinning on the in-stack bias layer is the key for stability. The narrower track-width heads have better stability. For in-stack biased bottom SV heads, the conventional structure has serious stability problem due to weakened or reversed bias field at free layer track edge. Controlling CPP edge profile is crucial for stability. We also studied the effect of current field on head performance. Depending on the current direction, current field can either induce instability or assist head stability. Index Terms--CPP spin valve read heads, in-stack longitudinal bias, stability.

Spin valve memory element biased with a pair of antiparallel (AP) coupled ferromagnetic layer was analyzed and modeled via micromagnetic simulation. In an AP structure, an external field results in a torque, causing the antiparallel magnetization (AP) axis to rotate towards the direction orthogonal to the field. In addition, due to its strength difference between the two AP layers, the magnetostatic field from the free layer of the spin valve can lead to irreversible AP axis flipping. This irreversible flipping can be effectively prevented by applying an AF/F exchange pinning to one of the AP layers to overcome the differential field from the free layer. Index Terms - Spin valve MRAM, synthetic antiferromagnet

Micromagnetic modeling of submicron size pseudo spin valve memory elements is presented. The storage mechanism of the memory system is proposed. For this mechanism, the switching field of the hard layer and the back switching field of the soft layer need to be well separated to ensure the non-destructive read-out. As the size of the element is reduced, the back switching field of the soft layer greatly increases. It is found that this back switching field can be significantly reduced by introducing a transverse anisotropy field in the soft layer. It is also found that the existence of an antiparallel edge domain configuration in the memory element can significantly degrade the performance of the memory cell and cause instability.

This paper presents a systematic micromagnetic analysis on spin valve GMR memory elements. It is found that for submicron size spin valve elements, edge demagnetization field, arising from the pinned layer, results in significant magnetization curling at the end edges of the free layer. This edge demagnetization phenomenon yields significant degradation of device performance. It is proposed that by making the pinned film element slightly longer than the free layer so that the ends of the free and pinned layers are separated, the edge demagnetization in the free layer can be essentially eliminated.

A micromagnetic study of synthetic antiferromagnet (SAF) biased spin valve heads with patterned exchange stabilization is presented. It is found that at deep sub-micron track widths, spin valve heads with the patterned exchange stabilization exhibit significantly higher read sensitivity than that stabilized with permanent magnet abutted junctions. It is also found that the canting of the exchange pinning field for the synthetic anti-ferromagnet layer off the vertical axis yields very different read sensitivity depending on the canting direction. Detailed analysis and explanation of the mechanism for the phenomenon are provided. It is concluded that the patterned exchange stabilization scheme can further extend the track density for the spin valve heads over the currently used stabilization scheme. Index Terms--Patterned exchange stabilization, spin valve heads.