M. Mirzamaani

10 Gbit/in.2 longitudinal media on a glass substrate (invited)

This article reports on the properties of the media prepared on glass substrates which were used in IBM’s 10 Gbit/in.2 demonstration. In order to support a linear density of 315 kbpi and a track density of 33 ktpi, the remanant coercivity Hcr and remanant moment thickness product Mrt of the magnetic layer were 3450 Oe and 0.37 memu/cm2, respectively. The media used a NiAl seed layer, a CrV underlayer, a Co alloy magnetic layer, and a carbon overcoat protection layer. The magnetic film had a grain size of 12 nm as observed by transmission electron microscopy. The preferred orientation (PO) of the magnetic layer was (1010). This PO enables one to sustain high coercivities at low values of Mrt. It is observed that the c-axis in-plane texture of the magnetic layer is critical to achieve a low noise medium. Using a focused-ion-beam (FIB) trimmed giant magnetoresistance head and conventional partial response maximum likelihood channel, the on-track-error rates were measured at the 10−10 level.

The effect of Cr underlayer thickness on magnetic and structural properties of CoPtCr thin films

Thin Co‐based alloy films have shown important recording, magnetic, and structural changes when grown on Cr underlayers of different thicknesses. We have investigated these properties using several different CoPtCr compositions on Cr underlayers ranging from 0 to 200 nm in thickness. We report epitaxial growth of the hcp Co (11.0) planes on the (100) planes of bcc Cr for the first time on a disk appropriate for magnetic recording. The 〈11.0〉 Co preferred orientation occurs only when the Cr underlayer has a 〈100〉 preferred orientation. The 〈100〉 preferred orientation in the Cr layer results from the use of sputtering rates above 150 nm/min and only persists to thicknesses of about 50 nm. The thin Cr underlayers (<50 nm) with a 〈100〉 preferred orientation have fine well‐packed grains. Thicker Cr underlayers have larger grains which are uncoupled and have a more random crystal orientation. The CoPtCr film morphologies follow these trends. The noise performance of these films improves with increasing Cr under...

Magnetic properties of CoPtCr thin films with 〈112̄0〉 crystal orientation

The microstructure and magnetic properties of CoPtCr thin films with 〈1120〉 restricted fiber texture grown on (100) planes of Cr single‐crystal films were characterized and subsequently correlated with the domain configuration during the magnetization reversal process. These films exhibited a bicrystal mode associated with two orthogonal easy axes of magnetization in the plane of the film. The domain configuration of these films during the magnetization‐reversal process consisted of two sets of domains extending in two orthogonal directions. These properties were compared with those of CoPtCr films with random crystallographic orientation.

Orientation ratio of sputtered thin‐film disks

Thin films of CoPtCr, with 15‐nm underlayers of Cr, were deposited by dc magnetron sputtering on NiP‐plated aluminum substrates that were textured (anisotropic roughness) or chemically etched (isotropic roughness). The relationships between the structure and the in‐plane magnetic properties were investigated. Under specific sputtering conditions, the Cr underlayer and the magnetic layer developed 〈100〉 and 〈11.0〉 crystallographic preferred orientations, respectively. The combination of 〈11.0〉 crystallographic preferred orientation and substrate texture resulted in an in‐plane uniaxial magnetic anisotropy, i.e., higher squareness and coercivity parallel to the texture lines. The films with the random crystallographic orientation exhibited the in‐plane magnetic isotropy on both the textured and the chemically etched Al/NiP substrates. The sputtering parameters and the substrate conditions that can lead to the development of in‐plane magnetic anisotropy were specified.

Recording Performance of Thin Film Disks with Various Crystallographic Preferred Orientations on Glass Substrates

CoPtCrTa films, with CrTi underlayer and a variety of crystallographic preferred orientations, were prepared on glass substrates. AlN, NiAl or Ta seed layers, deposited prior to deposition of the underlayer, were used to control the crystal orientation and grain size of the underlayer and thereby the magnetic layer. The correlation of magnetic and structural properties was studied. The media noise was found to depend primarily on grain size and grain size dispersion; the crystal orientation of the film had a secondary role. For a given CrTi underlayer, the [1010] preferred orientation was associated with the highest coercivity.

Correlation of thermal stability and signal-to-noise ratio of thin film recording media

The thermal stability of data stored in thin film recording media is closely tied to signal-to-noise ratio (SNR), yet is not correlated in a simple way. Indeed grain size strongly affects both SNR and thermal stability, but macroscopic magnetic properties as well as recording conditions are equally influential. This is illustrated by measurements of SNR and signal thermal decay along with a simple model analysis. Dependence of areal density on key magnetic properties, under SNR and stability constraints, is formulated.

Beyond 10 Gb/in/sup 2/: Using a merged notched head (FIB-defined writer and GMR reader) on advanced low noise media

We demonstrated recording performance at greater than 10 Gb/in/sup 2/ with data rates up to 25 MB/s, using a single combined write and read head (Merge Notched head).

Signal to noise ratio of thin film disks with various orientation ratios

Thin-film disks with various orientation ratios (OR) ranging from 0.5 to 4.3 were fabricated by sputter deposition of CoPtCr with Cr underlayers onto preheated NiP/Al-Mg disks. The recording characteristics of these disks were investigated using a thin-film head. The isolated pulse signal amplitude-to-media noise ratio (So/N) increased when OR was increased from 0.5 to 1 and then remained relatively constant for OR>or=1. An improvement of about 10 dB in overwrite of the disks with OR>1 was observed. >

Magnetic performance and tribology of sputter-textured thin film disks

A novel method for fabricating thin film disk media with controlled surface roughness via sputter deposition is described. This technique uses the deposition of a metal nitride such as AlN on a polished substrate to create discrete spherical features. The Cr or Cr alloy interlayer, the magnetic layer and the carbon overcoat are then deposited onto the AlN. The magnetic and mechanical performance of thin film disks fabricated with this technique Is presented and compared to that of a disk made with conventional mechanical texture. It is shown that the disks fabricated with this technique have no texture-induced noise, excellent magnetic performance, and tribological characteristics which make them suitable for high density recording applications.

Micromagnetic analysis of anisotropy orientation in high density longitudinal magnetic recording

Micromagnetic simulations have been performed to compare the recording performance of oriented media (Mr=1.50) with planar isotropic media in longitudinal recording. With no exchange, oriented medium exhibits substantially less dc noise power thus larger signal-to-noise ratio (SNR). But with increasing linear density, the oriented medium shows larger nonlinear amplitude reduction, larger nonlinear transition shift, and less SNR advantage. At finite exchange, there is no substantial SNR difference between oriented and isotropic medium.