P.R. Bissell

Interaction effects in the remanence curves of CoTi-doped BaFe systems

Measurements are reported on doped barium ferrite particles produced through chemical coprecipitation. The data are analyzed using a parameter Delta M(H). The behavior of Delta M(H) is reported to be strongly dependent on the doping and consequently the coercivity of the media. High-coercive-force media exhibit a net magnetizing effect in Delta M(H), which changes to a net demagnetizing effect as the coercivity decreases. This is interpreted in terms of changes in the particle interactions introduced through doping. >

Interparticle interactions in magnetic recording media as obtained from high-order measurements by a Preisach model

Generalized ΔM plots, which allow interactions to be investigated for any starting remanence state, have been used in the analysis of interactions in particulate magnetic recording media for three samples [very high speed (VHS) videotape, Ba-ferrite dispersed particles oriented and nonoriented]. The results have been interpreted using a generalized moving Preisach model. This gives a good fit to the hysteresis loops and ΔM plots. However, agreement with the generalized ΔM plots is less complete. This is interpreted in terms of a requirement for a magnetization dependent standard deviation in the generalized moving Preisach model.

Evaluation of statistical and mean-field magnetostatic interactions using generalized /spl Delta/m plots. experiments and preisach modeling

A new method for evaluation of the statistical and mean interaction fields in a particulate system is described. The Integral Generalized /spl Delta/M plot is introduced as the area of the Generalized /spl Delta/M plot against the starting remanent magnetic moment for the corresponding remagnetization process. This new plot is sensitive to the shape of the interaction distribution and to the value of the mean interaction field. The Integral Generalized /spl Delta/M plot provides an efficient way of distinguishing between the effects of the statistical and mean field interactions.

Interactions characterisation in particulate magnetic recording media. Experiments and Preisach model

Abstract New ways of experimental characterisation of interactions in particulate recording media have been investigated. Experimental procedures to obtain Δ M -like curves (generalised Δ M plots) which are sensitive to both statistical and mean-field interactions between the ferromagnetic particles in the system are analysed. The generalised Δ M plots allow Δ M -like plots to be produced from any reproducible initial remanent state. Another set of experimental curves sensitive to interactions are AC demagnetisation and anhysteretic remanent magnetisation. Measurements were performed on samples in the form of flexible particulate magnetic films (γ-Fe 2 O 3 VHS tape and Ba-ferrite dispersed powder films, oriented and not oriented) showing both positive and negative mean-field interaction effects. The experimental results were compared with the simulations made with a scalar generalised moving preisach model. There was good agreement between the theory and experiment for DC remanent magnetisation measurements but the fit was poorer for AC measurements.

Experimental and theoretical studies of transverse susceptibility in recording media

Introduction An experimental study of the transverse susceptibility xt has been undertaken. Measurements have been performed on various types of samples. In parallel with the expenmental work a model has been set up with a system of Stoner Woblfarth (S-W) particles. Good agreement is found between the experimental and theoretical characteristics of the k t response. Theory Aharoni eta1 developed a theoretical expression for x t for a random system. which we have generalised for some arbitrary texture function f(&, q6k) representing the distribution of easy axis directions. Thus;

Static and dynamic switching field distribution for magnetic tape systems

A low temperature (77K-300K) axial vibrating sample magnetometer, in which a specimen may be subjected to both AC and DC fields simultaneously, has been used to determine the static and dynamic magnetic properties of a professional quality γ-Fe 2 O 3 audio recording tape. The differential of the IRM curve was used to determine the switching field distribution (SFD) of the system. SFDs calculated in this way were compared with the equivalent parameters determined from AC melting curves. A significant difference was found which has been attributed to interparticle interactions.

A model of an isolated column of metal evaporated tape

Metal Evaporated (ME) tape comprises bundles of inclined columns each of which consists of small crystalline gains. To simulate the magnetic behaviour of ME tape we have developed a model, using a Monte Carlo algorithm to represent a single column of spherical grains whose radii are generated from a log-normal distribution. The dynamic process of the magnetic moments is explored by utilizing the Landau-Lifschitz equations. We demonstrate that the microstructure of the column and direction of the easy axes influence the magnetic reversal process. By varying the strength of the exchange coupling parameter its effect on the amount of co-operative switching is reported. The results suggest that high exchange coupling acts to keep moments aligned, resulting in higher values of coercivity. The reversal mechanism is initiated at the ends of the column and then propagates through the column.

Remanent state noise measurements on magnetic recording media

Abstract Media noise has been investigated as a function of both the isothermal remanent magnetisation (IRM) and DC-demagnetisation (DCD) processes on a modified audio transport. Captured noise time series from a given remanent state has been analysed for spectral content using signal processing software. These noise spectra display changes in magnetic microstructure of the tested media with remanent state. Measurements have been made on a range of commercial and laboratory produced tapes. The paper concentrates on examples of commercial samples which have been chosen to indicate various noise characteristics. Conventional media usually show similar features, but changes in remanent state noise has been observed in tapes for new formats and in recent manufacture of conventional formats. This indicates changes in magnetic microstructure associated with new particles and dispersion techniques.

The effects of texture and interactions on transverse susceptibility measurements of particulate media

Abstract The effect of texture and interactions on transverse susceptibility on systems of CrO 2 and Co-γ-Fe 2 O 3 particles has been studied. In samples of powder, dried dispersion and pseudo random hand spreads, the χ t response was significantly different to that of an aligned system. This study showed that the suppression of the H k peak in the CrO 2 powder and its absence in the Co-γ-Fe 2 O 3 powder could be explained by the texture of the system.

Interaction effects from reversal studies of single particles

Abstract Interaction effects within particulate recording tapes have been investigated by comparing single particle behaviour with measured tape bulk properties. The particle systems were audio γ-Fe2O3 and 8 mm MP video tapes plus CrO2 hand spreads. Interactions in the γ-Fe2O3 and CrO2 systems were negative and consistent with mean field behaviour. However, the MP particle interactions were in the opposite sense, in contradiction to the Henkel plots. A model for this behaviour involving the creation of chains is suggested.