J.P.C. Bernards

Investigation of Cr segregation within rf-sputtered CoCr films

Abstract Composition variations in thin transverse sections of rf-sputtered Co 78.5 Cr 21.5 films have been studied by X-ray microanalysis using a scanning transmission electron microscope. Analyses with a spatial resolution substantially better than 10 nm have shown that Cr rich regions exist in the boundary layers between 50–100 nm diameter columns which dominate the microstructure of such films. The extent of the measured Cr enrichment is≈1.5 at%, but when beam broadening effects are taken into consideration, the true segregation is found to be much greater. The implications of these results on the magnetic properties of the films are discussed.

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. >

Determination of local composition in Co-Cr films deposited at different substrate temperatures

Thin Co-Cr films deposited on polyester substrates at different temperatures have been investigated by high-spatial-resolution X-ray microanalysis. Films deposited on a substrate whose initial temperature was 90 degrees C had a columnar structure with distinct narrow boundaries whose composition, Co/sub 71/Cr/sub 29/, differed appreciably from that of the surrounding columns, Co/sub 77/Cr/sub 23/. By contrast, films deposited on a substrate at 30 degrees C had a columnar structure with less clearly defined boundaries whose composition did not differ significantly from that of the columns. These results help explain previously investigated magnetic properties of the films. >

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. >

Structural, magnetic and recording properties of Co-Cr layers for perpendicular recording using Ge nucleation layers

The influence of amorphous Ge underlayers on the structural, magnetic, and recording properties of Co-Cr recording media was studied. The media were prepared by RF sputtering on PET (polyethylene terephthalate) substrates just above room temperature. The Ge underlayer is observed to promote the perpendicular anisotropy of the Co-Cr, provided the Ge-layer thickness exceeds a critical value of about 200 nm to effectively seal the PET substrate. The resulting films also show low coercivity (10 to 30 kA/m), a columnar structure (column width 30 to 50 nm), and signal and noise features as described earlier for media, deposited at low temperature directly on the PET substrate. From the slope of the perpendicular hysteresis loop, the maximum in the noise spectrum, the noise periodicity and erasure experiments the medium domain period is estimated to be 370 to 780 nm for a 600 nm thick Co-Cr layer. These domain periods are consistent with a continuous perpendicular film model of the medium. >

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...

Observation of recorded tracks in Co-Cr media by magnetic force microscopy

Tracks recorded on two Co-Cr layers having coercivities of 15 kA/m and 45 kA/m were investigated by magnetic force microscopy. Different wavelengths were recorded, corresponding to bit lengths between 0.125 and 0.5 mu m. In the case of the layer with the low coercivity, the bits in a track recorded with a wavelength of 0.5 mu m were obscured by the meandering nature of the transitions, something which is not observed for the high coercivity layer. This is consistent with a higher noise level and a lower signal level for the low coercivity layer in recording experiments. A more detailed observation of the tracks in the high layer revealed the presence of subdomains in the recorded bits. The extent to which regular domain patterns (recorded bits) or more detailed magnetic structures can be observed depends on the size of the magnetic tip and the distance between tip and layer. The observed width of the intrinsic domains in these layers agrees well with calculated values. >