We report on magnetotransport measurements of spin valve films that have been fabricated into rectangular stripes with Au current leads. The spin valve films consisted of two magnetic NiFe layers separated by a nonmagnetic Cu layer. The top NiFe layer was magnetically pinned by a FeMn layer with an effective pinning field of 12 kA/m (150 Oe). After device fabrication, the transport properties changed dramatically as the stripe-height of the device was decreased below 1 μm. Internal demagnetizing fields and magnetostatic interactions between the magnetic layers dominated the magnetic response. These interactions change the biasing point and the linearity, and cause a decrease in sensitivity to field changes. We have developed a simple single-domain rotation model that includes magnetostatic, anisotropy, and exchange interactions to describe the magnetic behavior, from which we calculate the transport response.
We report second-harmonic magneto-optic Kerr measurements on air-exposed, polycrystalline Ni 81 Fe 19 thin films, ranging in thickness from 1 nm to 2 m, on Al 2 O 3 coated Si ͑001͒. For samples thicker than 20 nm, in the transverse Kerr geometry, we observe a factor of 4 change in second-harmonic intensity upon magnetization reversal. For thin samples, we observe interference between second-harmonic fields from the various interfaces and deterioration of ferromagnetism in the 1 and 2 nm films. Modeling suggests that the Ni 81 Fe 19 /Al 2 O 3 interface has a larger second-order susceptibility than the air/Ni 81 Fe 19 surface.
The effects of magnetostatic interactions on the giant magnetoresistive ͑GMR͒ response of NiFe/ Cu/NiFe spin valves are studied using an analytical model. The model is applicable to devices small enough for the magnetic layers to exhibit single-domain behavior. Devices having lengths in the track-width direction of 10 m and interlayer separations of 4.5 nm are studied. Stripe heights are varied from 0.5 to 2 m. The magnetization of one magnetic layer is pinned by a transverse pinning field that is varied from 0 to 24 kA/m ͑300 Oe͒. GMR curves for transverse fields are calculated. At zero external field the magnetization of the layers shows a tendency to align themselves antiparallel in the transverse direction. This results in an offset from the ideal biasing of the device. Broadening of the curves due to shape anisotropy occurs with decreasing stripe height and increasing magnetic layer thickness, and the magnetization in the pinned layer becomes less stable.
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