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Three techniques are compared that allow the magnetic thickness of recording media to be determined. The techniques rely on a measurement of the out-of-plane demagnetizing field and allow a standard vibrating sample measurement of a hysteresis loop to be calibrated in terms of magnetization. All three techniques give comparable results.

An extended method for anisotropy field measurements has been developed using a vector vibrating sample magnetometer (VSM). The technique, which relates the switching of particles nearly perpendicular to an applied field to the sample anisotropy, is suitable for magnetic media that contain orientated particles. Results measured as a function of angle are extrapolated to 90° for an improved measure of anisotropy field. In plane properties have been investigated for a series of four advanced double coated metal particle (MP) tapes. The results show that the in plane anisotropy field is related to the magnetic coating thickness, as a result of changes in magnetostatic interactions between the particles with thickness.

The magnetic characterization of four experimental advanced double-coated MP tapes with different magnetic coating thickness has been completed. Although standard vibrating sample magnetometer (VSM) measurements show very similar characteristics such as coercivity, squareness and orientation ratio (OR), alternative measurements show distinct differences in addition to their magnetic thickness. The in-plane distribution of easy axes (EAD) measured using a bi-axial VSM, show that the distribution width increased as the magnetic coating thickness decreased. A theoretical relation between OR and EAD was used to determine the out-of-plane distribution width. This was found to be narrower than the in-plane equivalent, as expected. The out-of-plane distribution width decreased as the magnetic thickness decreases, contrary to the in-plane variation.

This paper describes a model to test the validity of using the sheet demagnetising factor for advanced particulate tape magnetic measurements. The model predicts that, as the tape thickness and the volume packing fraction are reduced, the effective demagnetising factor deviates from the sheet value and, for a typical commercial advanced double coated MP tape, is in error by ∼6%.

Summary form only given. A method has been developed to measure the thickness of a magnetic coating on a particulate tape. This involves a determination of the demagnetizing field for the film by one of three methods including (1) transverse ac susceptibility (/spl chi//sub t/), (2) switching field measurement perpendicular to the applied field direction after the technique of Flanders and Shtrikman (1962) and (3) in-plane and out-of-plane hysteresis loop closure. The question arises as to the applicability of these measurements to thin film media. In fact, although the same principles apply, only the second method will give a satisfactory result. In case (1), transverse susceptibility measurement for commercial cobalt based sputtered films show virtually no reversible peaks. This is because the general expression for the transverse susceptibility contains a term dependent on k/sub 2/ = K/sub 2//K/sub 1/ and the orientation of grains. Since k/sub 2/ = 0.279 for cobalt, the grain orientation in a sputtered disk will cause a broadening of the transverse susceptibility peak to such an extent that it is immeasurable. This paper will further demonstrate the inapplicability of methods (1) and (3) for thin films and show a series of measurements using method (2) on a number of commercial disks to demonstrate its applicability.