C.P.G. Schrauwen

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. >

Magnetostatic and recording analysis of RF-sputtered double layer media for perpendicular recording

The paper describes the preparation, characterization and properties of RF-sputtered double-layer (DL) media for perpendicular magnetic recording. The media, consisting of CoCr on top of a soft magnetic NiFe layer, are deposited on Si wafers or polyester (PET) foils. The influence of an intermediate layer on the magnetic properties such as the NiFe coercivity, is described in terms of magnetostatic (de)coupling. In-contact recording experiments using ring heads include signal as well as noise measurements. Spike noise is observed in low-H c (NiFe) DL media, which probably may be ascribed to domain-wall displacements in the underlayer. The relation between the noise output and H c (NiFe) is shown.

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. >

CoCr double‐layered media with NiFe and CoZrNb soft‐magnetic layers (invited)

The magnetic, structural, and recording properties of CoCr double‐layered media are investigated. The underlayer materials NiFe (crystalline) and CoZrNb (amorphous) were combined with two different kinds of intermediate layers: Ti (crystalline) and Ge (amorphous). Applying a bias voltage during sputtering of NiFe results in a low coercivity of the NiFe layer and in a high coercivity of the CoCr layer. The structure of the NiFe layer influences the structure of the CoCr layer. A Ti layer between the NiFe and CoCr layers decreases the in‐plane remanence of the CoCr layer. The coercivity of all CoZrNb layers is low, independent of the application of a bias voltage. The orientation and structure of CoCr on CoZrNb can be improved by using a Ge intermediate layer, which results in a low coercivity of the CoCr. A Ti intermediate layer increases the coercivity. Ring heads show a dependence of spike noise on the underlayer coercivity and on the applied normal force. A probe‐type head shows a dependence of its outp...

Properties of one-sided probe heads on double-layer perpendicular recording media

The perpendicular recording mode is still a candidate for obtaining higher densities. Best recording results on a double-layer (DL) medium must be expected from using a probe head (PH). This contribution provides an analysis of the write-read performance of one-sided PHs that do not use an auxiliary pole on the back of the medium. Analytical as well as numerical models were used to calculate the effects of saturation and medium thickness on the write fields. Experimental verification of the modeling results was obtained by measuring the wavelength response of many W-shaped PHs on DL media. Combining this with the calculated response, we obtained a semi-empirical relation between the pole nulls, pole thickness and the pole-to-backlayer distance. It reveals a PH behaviour very different from a ring head (RH). The pole thickness calculated from the measured pole-null wavelengths showed a very close agreement with the optically determined value. The calculated head efficiencies are very small, as was confirmed experimentally, and need improvement before the PH has an output comparable with a RH.

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. >

Lateral magnetic inhomogeneities in Co-Cr layers detected by FMR

Co-Cr layers deposited on Ge underlayers were investigated with ferromagnetic resonance (FMR). The thickness of the Co-Cr layers and the substrate temperature (T/sub s/) during deposition were varied. Measurements with a vibrating sample magnetometer showed that an increase of T/sub s/ results in an increase of both the bulk saturation magnetization M/sub s/ and the perpendicular coercivity H/sub c//sup perpendicular to /. The FMR spectra, obtained with the applied field perpendicular to the sample, showed two resonances for all layers. The effective anisotropy field is positive for both resonances. The difference in effective anisotropy field does not change with thickness of the layer, but increases with increasing T/sub s/. From this it is clear that the two resonances are not due to magnetic inhomogeneities in the growth direction, but must be due to lateral magnetic inhomogeneities. Inhomogeneities in composition, resulting in different values of M/sub s/, or in geometric structure, resulting in different values of the demagnetizing factor N/sub d/, are the most probable causes of the observed effects. >

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. >

High performance heads for perpendicular recording

Several important features of past, present and future developments in the field of heads, specifically designed for perpendicular DL (double-layer) media, are outlined. The emphasis is probe heads (PHs) that are positioned on one side of the medium only. The fabrication and measurement of experimental, high-efficiency PHs, the so-called VSPs, are discussed. The experiments indicate that thin Co-Cr layers with a high coercivity are needed for a good short-wavelength response. This imposes several requirements on the pole material, such as a high saturation magnetization, low Barkhausen noise, and high permeability. A playback model is described that enables the head, medium, and interface parameters to be analyzed. The model has also been used to estimate the bit densities that can be obtained with PHs on DL media. An areal density of 1 bit/ mu m/sup 2/ appears feasible. >