Friction, wear and magnetic performance of metal evaporated and particulate magnetic tapes

Abstract

Metal evaporated (ME), metal particle (MP) and barium ferrite (BaFeO) magnetic tapes are leading candidates for ultra-high-density magnetic tape recording applications. Using a commercial video cassette recorder as a magnetometer and the Wallace equation, changes in the r.m.s. head output level were correlated to changes in head-to-tape spacing as tape wear occurred during play/rewind cycling tests. Interface stability and recording performance at a 0.6 μm recording wavelength were measured to bit level resolution using a drop-out counter. Some pause mode testing was done for comparison with streaming mode experiments. Methodologies to measure head and tape wear were developed and applied to worn specimens. Development of the experimental apparatus with nanometer vertical and submicrosecond temporal resolutions has enabled unprecedented understanding of the interplay of friction, wear and surface topography in a sliding contact. Waviness of ME tape and high roughness of BaFeO tape led to poor high-density recording performance as compared to the excellent performance of the flat MP tape. Interface stability generally improved as the tapes were used and worn smooth by the rotary heads, and head-to-tape spacing was reduced by about 10 nm over 1000 play/rewind cycles for the tapes. ME tape showed the least durability of all of the tapes, and damage areas initiated at high points or bumps on the tape surface were connected by lateral cracks (driven by longitudinal tension) across the tape width at tape failure after about 800 play/rewind cycles. MP tape performance improved gradually through 1000 play/rewind cycles. High asperities on the virgin tapes were severed off the tapes during the record pass, and those that remained on the tape surface increased friction force and tape wear by three-body abrasion early on in play/rewind cycling tests. Lower friction and virtually no wear were observed later in cycling tests when loose wear debris were no longer on the tape surface and the wear mechanism was adhesive. The wear coefficient in the streaming mode was larger than that in the pause mode due to abrasive particles in the contact interface in the streaming mode. MP and BaFeO tapes caused head stains on the metal core and glass surfaces of composite metal-in-gap heads. Anisotropic high tape stiffness led to asymmetrical head wear and head contours with large radii of curvature.