Pole tip recession in linear recording heads

Using a range of experimental techniques-optical and atomic force microscopy, and Auger electron spectroscopy-we have identified the major processes responsible for pole tip recession (PTR) in linear tape recording systems. Within a few tens of hours, TiC grain fragments pulled out from the tape-bearing surface ceramic (Al₂O₃-TiC) are trapped in the pole tip region and, hence, act as three-body abrasive particles. This dramatically increases PTR. We used a numerical model to calculate the depth of the head subsurface von Mises stress maximum. The result (a depth of about 30 nm) is comparable to the TiC pullout depth. A fatigue mechanism is thus likely to rely on generation and propagation of cracks at that depth, which causes TiC grains to pull out. To overcome this phenomenon, we considered two solutions. 1) Recording heads coated with two different superprotective layers (SPL)-CrO₂ coating-thicknesses, 20 and 40 nm, were tested in various environments. The maximum stress location, either in the substrate (20-nm SPL) or at the interface (40-nm SPL), was found to control the coating wear resistance. 2) Dummy heads consisting of a single-phase ceramic (Al₂O₃) as an alternative to Al₂O₃-TiC were also tested; no evidence of fatigue brittle fracture was found.