Inertia effects on static friction measurements of laser textured media [magnetoresistive recording heads

Abstract

Mechanical and magnetic requirements for Magneto-Resistive (MR) recording heads have caused media data zones to become increasingly smoother. Tribology conditions of the landing zone still require some roughness, however. Because of this, dual zone textured media has become a common solution for MR applications. Although some disks have been dual zone textured mechanically, laser textured landing zones have become an industry standard. Laser textured media has unique static and dynamic friction properties, and if careful attention is not paid to measurement set-up, measured static friction values could be extremely inaccurate (up to 100%). This is likely due to system inertia differences and a difference in /spl zeta//sub k/ (The ratio of Dynamic to True Static Friction). While mechanically textured media has typical /spl zeta//sub k/ values ranging from 0.4 to 0.6, laser textured media has typical values close to 1.0. A theoretical model of breakaway friction measurements by Li et al. predicts the above mentioned trend. The model shows that /spl zeta//sub p/ (The sensed to true static friction ratio) varies as a function of /spl zeta//sub i/ (The inertia force to true static friction ratio). This function is different for different values of /spl zeta//sub k/. The model predicts that laser textured media will be much more dependent on inertia force than mechanically textured media. The trend predicted by this model is now demonstrated experimentally. By using a small DC motor to drive a spindle, it is possible to reduce the instantaneous acceleration to an extremely low value. When measuring stiction at these extremely low acceleration rates, it is demonstrated that the measured values are much lower than they are when measured at higher acceleration rates. Even though laser textured media with a carbon coated MR head exhibits this phenomenon, a mechanically textured disk with a non-carbon coated inductive head does not (in the range of accelerations tested).