Micromechanical and tribological characterization of alternate pole tip materials for magnetic recording heads

Abstract

Pole tip recession or PTR (relative wear of the pole tip with respect to the air bearing surface) causes signal loss when using inductive heads. Loss of signal caused by spacing between a head gap and the recording medium is magnified in high-density short wavelength recording. Nickel iron (NiFe) is the most commonly used pole material. NiFe is softer than the head substrate material (typically NiZn ferrite or Al 2O 3TiC) which leads to PTR as a result of differential wear of the materials. Alternate pole tip materials which are more wear resistant and superior in magnetic properties (such as high saturation magnetization), as compared with NiFe, need to be developed. In this research, NiFe, cobalt zirconium tantalum (CoZrTa) and iron aluminum nitride (FeAlN) materials were studied. In the first phase of this study, micromechanical characterization of the three pole tip materials, the alumina (Al 2O 3) insulating under/overcoat and gap material and the Al 2O 3TiC substrate was conducted using a depth-sensing nanoindenter. The nanohardness of NiFe, CoZrTa and Al 2O 3 are similar and about one half that of FeAlN, and the hardness of the Al 2O 3TiC substrate is about twice that of FeAlN. Microscratch studies showed that the critical load required to cause failure of the NiFe and CoZrTa films are similar and about one fourth that of FeAlN, and the critical load for FeAlN is comparable with that of the Al 2O 3 and Al 2O 3TiC substrate. Thus, FeAlN is superior in mechanical properties to NiFe and CoZrTa. In the second phase of this study, dummy tape heads fabricated with the three pole materials were run against metal particle (MP) tape in a linear tape drive. The PTR was measured by atomic force microscope (AFM) imaging before and after the sliding tests. Any nonuniformities in the thin-film region gets removed in the first few kilometres of sliding. FeAlN poles exhibited a low (∼10 nm) and constant PTR over 1 000 km of tape sliding distance, whereas the NiFe and CoZrTa poles exhibited growth in recession to about 30 and 40 nm, respectively, over the same sliding distance. The superior wear resistance and high saturation magnetization of FeAlN are ideal for high-density thin-film inductive heads.