H.A.J. Cramer

Vector magnetisation of recording media: a new method to compensate for demagnetising fields

Until now measurements of M(H) loops of thin samples have been corrected for demagnetization after completion of the measurement. In this way, it is possible to correct for the component of the demagnetizing field which is parallel to the applied field. The authors present a method to correct for the total demagnetizing field during the measurement by simultaneously changing the strength of the applied field and rotating the sample. This method has been applied to a sample of metal-evaporated (ME) tape and a Co-Cr layer. These measurements show that the method is significantly better than existing methods. It is shown that the intrinsic magnetic properties of the ME tape and the Co-Cr layer measured with the method are remarkably similar. >

A moving preisach vector hysteresis model for magnetic recording media

Abstract Two hysteresis models commonly used in numerical simulations of the recording process are the Preisach model and the particle assembly model. A combination of these models is presented which includes the mean field approach of the moving Preisach model. It is shown how the model can be tailored to enable an efficient numerical implementation. Comparison of the results with different experimental loops of a metal particle tape and a barium ferrite floppy disc reveals that this model has good vector properties and reproduces the different remanence loops well. The different interaction terms in the model are investigated separately. It is shown that the narrow switching field distribution of barium ferrite and the typical interaction phenomena reported by other authors can both be ascribed to a mean field interaction parallel to the particle axis.

High bit density (100 Mb/cm/sup 2/) with single-layer Co-Cr media and ring heads in perpendicular magnetic recording

The signal and noise of single-layer Co/sub 79/Cr/sub 21/ media are measured with ring heads to estimate the area density that can be achieved. Densities as high as 100 Mb/cm/sup 2/ (1 mu m/sup 2//bit) are expected when a signal-to-noise ratio sufficient for an error probability less than 10/sup -5/ is required. As a comparison, densities estimated from data from metal-evaporated tape and CrO/sub 2/ tape are given. In the frequency response of the single-layer media, an additional minimum was observed for a wavelength slightly larger than the gap length. This is probably caused by the bipolar nature of the perpendicular recording field of a ring head. >

Simulation of the recording process on Co-Cr layers with a VSM

To investigate the role of both perpendicular and in-plane head field components in the recording process, a ring head writing transition in Co-Cr layers was simulated with a vibrating sample magnetometer by changing the field strength and rotating the sample simultaneously. The magnetization components parallel and perpendicular to the field direction were measured. An increase in perpendicular magnetization, which can be larger than 50% at the center of the transition, and a decrease in in-plane magnetization were found in the case where the head field was switched compared to the case where the head field was not switched. These effects decrease with increasing maximum field values and with decreasing effective perpendicular anisotropy of the layer. The in-plane field component appears to play an important role: without this component, these effects were not observed. The results are consistent with recording experiments with ring heads and prove that the extra minima in the frequency response described in an earlier paper have a micromagnetic origin. >

Simulation of the recording process with a VSM on Co-Cr and Co-Ni-O layers deposited at oblique incidence

The recording process on Co-Cr and Co-Ni-O layers deposited at oblique incidence is simulated with a vibrating sample magnetometer. The Co-Cr layers are deposited on Si substrates and have an easy magnetization direction tilted 15 degrees from the normal to the layer, which is caused by the presence of columnar-shape anisotropy. The simulation experiments show that such a layer is more sensitive to one side of the perpendicular component of the write field of a ring head. The Co-Ni-O sample has an easy direction of magnetization tilted about 20 degrees out of the plane. The simulation experiments show that the steepness of the transition is different for the two directions of head movement. >

Write-field interference in the recording process on Co-Cr media: an experimental study

The frequency response of Co-Cr media, recorded with a ring head, shows a series of additional minima. Investigation with a write head with a large gap (3 mu m) revealed that the effect can be modeled as a double transition recorded by the fields at the leading and trailing edges of the head. It was found that the magnitude of the second transition decreases when the recording current is increased above the optimum value. The thickness of the Co-Cr layer has no significant influence on the magnitude of the minima. However, a decrease of the effective perpendicular anisotropy results in a smaller magnitude of the minima. These observations are confirmed by VSM simulations. >

Remanence curves of thin-film media with a tilted easy magnetisation direction corrected for demagnetisation

Abstract Remanence curves have been measured of metal evaporated tape with a tilted easy magnetisation direction. A method to compensate for the demagnetising field was applied. The δ m curve along the intrinsic easy direction shows combined positive and negative interactions, along the intrinsic hard direction only negative interactions. These results could be reproduced with a moving-Preisach Stoner-Wohlfarth hysteresis model.

Perpendicular recording with a one-sided MiG-head on single-layer Co-Cr

A one-sided MIG (metal-in-gap) head is proposed for perpendicular recording on single-layer Co-Cr layers. When the recording current is sufficiently high, saturation sets in at the pole tip at the ferrite side of this head, while the sendust side is still recording well. This results in an asymmetrical recording field. The recording interference between the fields at each side of the gap which deteriorates the output when a normal ring head with symmetrical head field is used to record on Co-Cr media, is no longer observed. As a consequence of the asymmetrical head field, the recorded magnetization is more perpendicular and the low-frequency output is higher. >

Correlation of particle length and radius: a new model for flux noise in particulate media

Several theoretical models for predicting the flux noise of particulate media are reviewed, and a statistical model that stresses the correlation between particle radius and particle length is proposed. The predictions from this model are much more wavelength-dependent than in previous models. This dependence is already exhibited at wavelengths that are an order of magnitude larger than median particle length. The model is empirically supported by particle-size measurements. >

An improved detection coil system for a biaxial vibrating sample magnetometer

Abstract A detection coil system, consisting of 12 coils, for use in a biaxial vibrating sample magnetometer is described. For such a coil system the dependence of the sensitivity on the position of the sample is much smaller than for other systems, not only for the detection of the magnetisation component in the direction of the applied field, but also for the detection of the magnetisation component perpendicular to the applied field.