Magnetic characterization of perpendicular recording media

• Published in: IEEE transactions on magnetics 2002-07, Vol.38 (4), p.1682-1686
• Main Authors: Jing Wu, Holloway, L., Laidler, H., O'Grady, K., Khizroev, S., Howard, J.K., Gustafson, R.W., Litvinov, D.
• Format: Article
• Language: English
• Subjects: Alloy systems; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Demagnetization; Exact sciences and technology; Force magnetometers; Force measurement; Information storage; Isothermal processes; Joining; Kerr effects; Magnetic hysteresis; Magnetic properties and materials; Magnetic recording materials; Magnetic storage; Magnetic tape; Magnetism; Magnetization; Magnetization curves; Magnetometers; Perpendicular magnetic recording; Physics; Recording; Recording instruments; Remanence; Shape measurement; Studies of specific magnetic materials; Vibration measurement
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2002.1017756

In this paper, we describe techniques for the magnetic characterization of perpendicular recording media. Such measurements made using traditional techniques, such as the vibrating sample magnetometry (VSM) and alternating gradient force magnetometer (AGFM), have to be corrected for the sample shape demagnetizing factor, which is often found not to be equal to -4/spl pi/. For measurements other than the simple hysteresis loop, such as remanence curves, this correction must be carried out in real time and we describe the method by which this can be achieved and the process for achieving the correct demagnetization of perpendicular films prior to measurements of the isothermal remanent magnetization curve. A further complication is that real perpendicular media have a soft underlayer beneath the recording layer, which swamps and confuses signals from instruments such as VSM or AGFM. Hence, we describe the construction and use of a magnetooptical Kerr effect magnetometer, which does not penetrate significantly into the soft layer and enables the perpendicular layer to be measured independently. We describe the properties of a traditional alloy perpendicular medium and a Co-Pd multilayer system, which in the latter case exhibits multiple switching behavior. We also address the issue of the effect of the soft underlayer on the coupling in similar longitudinal films and find that the presence of the underlayer induces significant additional coupling effects that may well give rise to an increase in noise in recorded signals.