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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.Introduction Magnetic recording media are often textured during manufacture by increasing the alignment of particle easy axes. The degree of texturing can be described by the Easy Axis Distribution (EAD) which can be different in-plane and out-of-plane. The effect of texturing increases the squareness of the hysteresis loop and reduces the switching field distribution (SFD), which is beneficial to recording performance. For simplicity of characterization, texture is often represented by the orientation ratio (OR). This is defined as the ratio of the remanent magnetization along the recording direction to that transverse to it. For randomly orientated particles OR = 1, while an OR > 1 indicates a partial alignment of the particles [1]. OR is a crude measure, which is insensitive to the distribution width for OR in the range 1 to %2 and a full measurement of the distribution of easy axes gives more detail. Several techniques have been developed to measure the in-plane EAD using either torque magnetometry [2, 3] or using vibrating sample magnetometer measurements [4,6]. Most techniques are derivatives of the method introduced by Flanders and Shtrikman [5]. This is the case for our measurements, which were performed using a bi-axial VSM technique that was implemented by Schmidlin et al. [6].

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 o 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.Introduction The anisotropy field and its distribution is a very important parameter for determining potential applications of magnetic recording media. In commercial applications, recording media properties are generally characterized by standard hysteresis parameters such as the coercivity. However, this is related not only to the magnetic particle properties but also to way the particles are incorporated into the matrix, such as the orientation of the particle easy axes. The advantage of anisotropy field distribution measurement is that, although the particle interactions still influence the results, other properties of the matrix are excluded so that results relate more to the potential of a "particle type" to the application rather than to the specific coating under investigation. This is because a single domain particle makes a contribution to the anisotropy field related to its switching field when its easy axis is aligned with the applied field but it is still under the influence of interactions with other constituent components of its magnetic environment. On the other hand, the particle contribution to coercivity is related to its switching field with the particle easy axis in its present orientation to the applied field. Many techniques have been developed to measure the anisotropy field and anisotropy field distribution using remanent torque magnetometry [1,2] or vibrating sample magnetometer (VSM) measurements [3,4]. Rotational hysteresis has also been extensively used for effective anisotropy field measurements [5,6]. Many of the techniques determine the anisotropy field using experiments which involve switching processes. Anisotropy field can be also measured using non-switching techniques, such as transverse susceptibility. Sollis and Bissell [7] have been used transverse susceptibility for anisotropy field measurements and magnetic thickness calculation on CrO 2 systems. In this paper, we describe a method for determination of the anisotropy field distribution and the effective mean anisotropy field of the particles using a biaxial VSM. The technique is an extension of the remanent magnetometry method described

The methods used for measuring the Anisotropy Field Distribution (AFD) could be classified into switchins (involving irreversible magnetization processes, e.g. Rotational Hysteresis Loss) and stiff (involving reversible processes, e.g. hard axis loop). Because the irreversible processes are thermally activated, the switching fields and consequently the HK values measured by switching methods are decreased with respect to their intrinsic values because of thermal relaxation. The goal of this work is to explain the difference between the AFDs measured by switching and stiff methods for both, longitudinal and perpendicular recording media. Using the Maximum Entropy Method, it is shown that the almost two times lower values for HK obtained for CoCrPtB-type longitudinal thin films (hard disk media) by switching methods with respect to those given by stiff methods are due to thermal relaxation. Particle interactions are shown to act only on the width of the AFD, without affecting the position of its maximum (Fig.1a). Better agreement between the AFDs found using switching and stiff methods was obtained for perpendicular than for longitudinal media, that was interpreted as the effect of both, the high texturing degree and the higher stability factor for the perpendicular medium (Fig. IC). In order to correct the AFD obtained by switching methods for the effects of thermal relaxation, one needs an estimation of the particle switching volume VSW. In this work, a new model for estimating VSW using the field sweep rate dependence of coercivity Hc(R) is described. The results regarding HK and KV/(kBT) given by the proposed model are compared with those obtained using the time dependence of coercivity Hc(t) and remanence coercivity HRC(t) and good agreement is obtained for both, longitudinal and perpendicular media. 1 5 O h P 0 5 2 1. 16 18 20 0 0 1.5 h 1 .o v P 0.5 3-0.0 0 2 4 6 8A method has been developed to measure the thickness of a magnetic coating on a particulate tape [l]. This involves a determination of the demagnetizing field for the film by one of three methods including (1) transverse ac susceptibility (xJ, (2) switching field measurement perpendicular to the applied field direction after the technique of Flanders and Shtrikman [2] and (3) inplane 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 Ijl .)n, principles apply, only the second method will give a satisfactory result. In case (l), transverse susceptibility measurement for commercial cobalt based sputtered films show virtually no reversible peaks. This is because the general 4 * 0 * 1 expression for the transverse susceptibility [3] contains a term dependent on k, = K2 / K , , and the orientation of grains. Since kZ = 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. Fig. 1 is a simulation of a xt for a planar random Co thin film. The larg...