Studies of reversal processes in particulate recording media using pulsed field magnetometry

This investigation details the development of two pulsed field magnetometers which allow novel measurements of particulate recording media to be performed. The samples studied are indicative of advanced metal particle recording media which are currently utilised for high density data storage applications, such as Imation Travan"T"M linear tape. In the first part of this investigation, a magnetometer has been developed to study reversal processes in metal particle dispersions. The instrument consists of a MOSFET pulse generator which produces well-defined current pulses of over 125A, with selectable pulse widths between 25#mu#s and 130#mu#s. The current pulse is driven into a small field coil assembly, the geometry of which is such that a magnetic field of over 4.7kOe is generated, with symmetrical rise and fall times of around 15#mu#s. Extensive proving studies are presented, which reveal that differences in chemical formulation and dispersion quality may be monitored through pulsed remanence curves. The second part of this investigation concerns the highly topical issue of high speed reversal in particulate media. A 50#OMEGA# pressurised nitrogen spark gap switch has been developed, capable of producing well-defined single-shot voltage pulses of over 3kV. The pulse width is adjustable from 7ns to 56ns, with rise times of under 3ns. The magnetometer consists of a charged coaxial line connected through the spark gap to an improved 50#OMEGA# microstrip structure, the geometry of which allows pulsed magnetic fields to be produced with a maximum amplitude of 1.8kOe. Again, extensive proving studies have been performed and the results are compared with recent models of thermally activated reversal. These pulsed field studies have revealed a correlation between the degree of particle orientation in the tape and high speed reversal properties. The origins of this effect are complex, and are related at different timescales to the crystallite or activation volume, particle interactions and phenomena influenced by gyromagnetic effects. The implications of this are that larger head fields are required to write high frequency transitions on increasingly textured systems. Clearly, this promotes conflicting requirements in terms of recording performance and media durability. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN032937 / BLDSC - British Library Document Supply CentreGBUnited Kingdo