We present the dependence of the magnetostriction in Ni 0.8 Fe 0.2 films on Tb and Gd doping concentration and compare with the measured doping dependence of the high-frequency damping. While the magnetostriction and the high-frequency damping are correlated, the dependence is complicated. In particular, the high-frequency damping parameter ␣ increases rapidly (␣ ϭ0.008-0.84) with a modest increase in the magnetostriction ͑ s ϭϪ0.6ϫ10 Ϫ6 to 5.7ϫ10 Ϫ6 ͒ for Tb doping concentrations up to 10%. For Gd doping, the high-frequency damping changes slowly ͑␣ϭ0.008 -0.02͒ as the doping concentration is increased to 10%, whereas the increase in magnetostriction is similar to that observed in the Tb-doped films. Further, it is possible to achieve low magnetostriction ( s ϭ2ϫ10 Ϫ6 ) near the region of critical damping. Measurements of the angular dependence of the ferromagnetic resonance linewidth in Tb-doped Ni 0.8 Fe 0.2 films show little change similar to the behavior observed in undoped Ni 0.8 Fe 0.2 films, although the linewidths are considerably larger. This is in contrast to systems such as Ni 0.8 Fe 0.2 on NiO, which have a large angular dependence indicating that the relaxation process proceeds through the generation of spin waves. The enhanced damping in the Tb-doped films appears, therefore, to be mediated through direct phonon generation.

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The modification of film anisotropy (Hk) after the establishment of an air bearing surface (ABS) due to the interaction of anisotropic stress and film magnetostriction is well known.' A resultant increase in Hk has been found to degrade the sensitivity of an unshielded magnetoresistive (MR) sensor. Similar results have been reported for barber pole biased MR heads.2 For M R sensors biased by a soft adjacent layer (SAL) the effect of the stress induced Hk takes on additional ci~mplexities. The overall device transfer function can be profoundly affected due to the interplay between the two films, resulting in severe nonlinear distortions. We have studied unshielded SAL biased M R sensors with the MR film thickness at 300 A and the magnetostriction coefficients (A) near zero and at -3~10-6. After ABS fabrication the sensor geometry is 3.5 pm in height and 120 pm in length. With near-zero 1 for both films the transfer function assumes the normal quadratic shape (Fig.1). With the negative MR L the transfer function develop5 a kink near the operating point with the sensitivity reduced abruptly beyond the kink (Fig.2). In a recording application this will result in severely distorted pulse\ of the negative polarity. T o understand the phenomenon we have constructed an uniform rotation model with elliptical approximation for the demagnetizing field. The model describes very well the device behavior for near-zero MR I (Fig.3). For the negathc MR 1 we have assumed a stress induced Hk of 10 Oe in the MR film along the stripe (Fig.4), which corresponds to a compressive stress of 0.9~109 dyne/cm2. The modrling results reveal that the kink in the transfer function develops when the SAL comes out of saturation (Figs). The operation of the device thus can be divided into two regions. In one region the SAL stay saturated and only the MR layer responds to the external field, resulting in the expected quadratic response. In the other region thr SAL is no longer saturated, and both layers respond to the field, resulting in an nbrupt change in senritivity. The two regions for SAL biased MR heads always exist as evidrnced in even the de\.ice with near-zero MR 1. The transition between the two regions is a result of energy balance between the MR layer and the SAL. The transition can be affected by many parameters, and rhould be an important consideration in SAL biased MR heads designs. Field (20 Oe/div) Fig I Transfer function of zero 1 *---_ -8W 0 tW Field (Oe) Fig 3 Modeling of the transfer functlon with zero MR 1 Field (20 Oejdiv) Fig.2 Transfer function of nagalive MR 1 I o / i Field (Oe) Fig 4 Modeling of the transfer function with negative MR 1 ' : / I i ' I -7 0 0 0 IW Field (@I Fig 5 Rotation of the MR and SAL magnetmtion.